Materials Science › Materials Chemistry

Solid-state spectroscopy and crystallography

Works Count: 106658

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This cluster of papers explores the use of solid acids as fuel cell electrolytes, focusing on their protonic conduction and ferroelectric properties. The papers cover topics such as high-temperature behavior, crystal structure, dielectric properties, phase transitions, and the application of nuclear quadrupole resonance in studying these materials.

Keywords

Solid Acids; Protonic Conduction; Ferroelectricity; Fuel Cells; Electrical Properties; Crystal Structure; Dielectric Properties; Phase Transitions; Nuclear Quadrupole Resonance; High Temperature Behavior

Infrared spectra of inorganic and coordination compounds

1963-01-01

Kazuo Nakamoto

Theory for displacive excitation of coherent phonons

1992-01-01

H. J. Zeiger , J. Vidal , T. K. Cheng +3 more

We report femtosecond time-resolved pump-probe reflection experiments in semimetals and semiconductors that show large-amplitude oscillations with periods characteristic of lattice vibrations. Only ${\mathit{A}}_{1}$ modes are detected, although modes with other … We report femtosecond time-resolved pump-probe reflection experiments in semimetals and semiconductors that show large-amplitude oscillations with periods characteristic of lattice vibrations. Only ${\mathit{A}}_{1}$ modes are detected, although modes with other symmetries are observed with comparable intensity in Raman scattering. We present a theory of the excitation process in this class of materials, which we refer to as displacive excitation of coherent phonons (DECP). In DECP, after excitation by a pump pulse, the electronically excited system rapidly comes to quasiequilibrium in a time short compared to nuclear response times. In materials with ${\mathit{A}}_{1}$ vibrational modes, the quasiequilibrium nuclear ${\mathit{A}}_{1}$ coordinates are displaced with no change in lattice symmetry, giving rise to a coherent vibration of ${\mathit{A}}_{1}$ symmetry about the displaced quasiequilibrium coordinates. One important prediction of the DECP mechanism is the excitation of only modes with ${\mathit{A}}_{1}$ symmetry. Furthermore, the oscillations in the reflectivity R are excited with a cos(${\mathrm{\ensuremath{\omega}}}_{0}$t) dependence, where t=0 is the time of arrival of the pump pulse peak, and ${\mathrm{\ensuremath{\omega}}}_{0}$ is the vibrational frequency of the ${\mathit{A}}_{1}$ mode. These predictions agree well with our observations in Bi, Sb, Te, and ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$. The fit of the experimental \ensuremath{\Delta}R(t)/R(0) data to the theory is excellent.

Electronic Population Analysis on LCAO–MO Molecular Wave Functions. II. Overlap Populations, Bond Orders, and Covalent Bond Energies

1955-10-01

Robert S. Mulliken

LCAO molecular orbital overlap populations give in general much more flexible and widely useful measures of the non-Coulombic parts of covalent bond energies than do LCAO bond orders. They are … LCAO molecular orbital overlap populations give in general much more flexible and widely useful measures of the non-Coulombic parts of covalent bond energies than do LCAO bond orders. They are immediately applicable to both π and σ bonds, including bonds involving hybrid AOs of all kinds, and they take account directly of the effects of variations in bond length on bond strength. In the last section of this paper, a number of ways of defining LCAO bond orders are reviewed, and their advantages and disadvantages discussed. If all LCAO parameters β are assumed proportional to corresponding overlap integrals S times suitable mean atomic ionization energies Ī, a simple general approximate formula for covalent resonance energies is obtained in terms of partial overlap populations and Ī's, including one or two empirical coefficients. This formula indicates that forced hybridization (see III of this series) due to inner shells should make important negative contributions to bond energies. The application of the formula to H2, CO, and H2O is discussed. The assumption of proportionality of β values to SĪ values may be useful also in estimating unknown β values.

On the Polar Vibrations of Alkali Halides

1941-04-15

R. H. Lyddane , R. G. Sachs , Edward Teller

The long wave-length, polar lattice vibrations of alkali halide crystals are discussed without making any specific assumptions about the detailed interactions between the ions. This is made possible by the … The long wave-length, polar lattice vibrations of alkali halide crystals are discussed without making any specific assumptions about the detailed interactions between the ions. This is made possible by the introduction of the effective charge, ${e}^{*}$, of an ion defined as follows: All of the positive ions in a crystal slab are displaced by an equal amount in a direction perpendicular to the faces of the slab and all of the negative ions in the opposite direction. Then ${e}^{*}$ is the ratio of the dipole moment per ion pair induced in the slab by this displacement to the relative displacement of the positive and the negative ions. Expressions are obtained for the frequency, ${\ensuremath{\omega}}_{l}$, of the longitudinal vibration and the frequency, ${\ensuremath{\omega}}_{t}$, of the transverse vibration in terms of the dielectric constant, $k$, of the crystal, the dielectric constant, ${k}_{0}$, obtained by extrapolating the square of the index of refraction of the crystal from high frequencies to zero frequency, and ${e}^{*}$. The ratio of the two frequencies is found to be independent of ${e}^{*}$ and given by $\frac{{\ensuremath{\omega}}_{l}}{{\ensuremath{\omega}}_{t}}={(\frac{k}{{k}_{0}})}^{\frac{1}{2}}$.

An infrared study of pyridine adsorbed on acidic solids. Characterization of surface acidity

1963-10-01

E. P. Parry

On the interaction of nuclear spins in a crystalline lattice

1949-05-01

N. Bloembergen

Solitons in conducting polymers

1988-07-01

Alan J. Heeger , Steven A. Kivelson , J. R. Schrieffer +1 more

Self-localized nonlinear excitations (solitons, polarons, and bipolarons) are fundamental and inherent features of quasi-one-dimensional conducting polymers. Their signatures are evident in many aspects of the physical and chemical properties of … Self-localized nonlinear excitations (solitons, polarons, and bipolarons) are fundamental and inherent features of quasi-one-dimensional conducting polymers. Their signatures are evident in many aspects of the physical and chemical properties of this growing class of novel materials. As a result, these polymers represent an opportunity for exploring the novel phenomena associated with topological solitons and their linear confinement which results from weakly lifting the ground-state degeneracy. The authors review the theoretical models that have been developed to describe the physics of polyacetylene and related conducting polymers and summarize the relevant experimental results obtained for these materials. An attempt is made to assess the validity of the soliton model of polyacetylene and its generalization to related systems in which the ground-state degeneracy has been lifted.

Spin-lattice relaxation in rare-earth salts

1961-12-05

R. Orbach

A general approach to spin-lattice relaxation is given for salts to which a crystalline field theory is appropriate. In particular, the theory of Elliott & Stevens for the interaction of … A general approach to spin-lattice relaxation is given for salts to which a crystalline field theory is appropriate. In particular, the theory of Elliott & Stevens for the interaction of a rare-earth ion with static ionic surroundings is generalized phenomenologically to represent the interaction of the rare-earth ion with the lattice vibrational modes. Evaluation of the spin-lattice interaction in terms of a few constants is possible. One- and two-phonon processes are investigated and the relaxation times for non-Kramers and Kramers salts computed. For the one-phonon (or direct) process the non-Kramers salts exhibit the typical behaviour T 1 ∝ H -2 T -1 , and the Kramers salts T 1 ∝ H -4 T -1 . It is shown that, for a given Zeeman splitting of the ground doublet, the latter may exhibit an enormous anisotropy with respect to the direction of the external field, approximately proportional to the anisotropy of the temperature-independent part of the susceptibility. Application of the general theory is made to two salts, holmium and dysprosium ethyl sulphate; the former a non-Kramers, the latter a Kramers salt. It is shown that the dysprosium salt would be expected to show a relaxation time in the direct process region which will vary as sin -2 θ cos -2 θH -4 T -1 , where θ is the angle the external magnetic field makes with the crystallographic symmetry axis. For two-phonon processes, the additional distinction of whether the Debye energy ( Kθ D ) is less than or greater than the crystalline field splitting Δ between the ground state and the first excited state must be made. Non-Kramers salts to which the former condition apply ( Kθ D < Δ) are shown to possess two-phonon relaxation processes of the usual Raman type. The relaxation time is proportional to T -7 and is independent of magnetic field. When Kθ D > Δ, there is present in addition a term arising from a resonance process, analogous to the resonance radiation effect in gases. Phonons of energy ~ Δ are absorbed and emitted by the spin system preferentially because of a phonon resonance with the crystalline field splitting of the spin states. As normally KT is much less than Δ, this leads to a relaxation time proportional to exp (Δ/ KT ). This process will dominate the Raman process except at very high and low temperatures. It is shown to be significant right down to the liquid-helium range by comparison with the relaxation rate due to direct processes. Kramers salts, when Kθ D < Δ, owing to a cancellation in the rate equation, exhibit a Raman relaxation time proportional to T -9 and independent of field. This 'Van Vleck cancellation’ is shown to be a consequence of time reversal symmetry. When Kθ D > Δ, the resonance process is also present, the relaxation time again being proportional to exp (Δ/ KT ). The resonance process is now shown to be dominant down to 1 or 2 °K for many rare-earth salts. Experimental verification is found for the resonance relaxation process in the rare-earth ethyl sulphates. In general, it is expected that this mechanism will be significant for any magnetic salt in which Kθ D > Δ.

Electroelastic Properties of the Sulfides, Selenides, and Tellurides of Zinc and Cadmium

1963-02-01

D. Berlincourt , Hans Jaffe , L. R. Shiozawa

A complete set of elastic, piezoelectric, and dielectric constants is presented for the sulfides, selenides, and tellurides of zinc and cadmium. The piezoelectric constants for the hexagonal crystals in this … A complete set of elastic, piezoelectric, and dielectric constants is presented for the sulfides, selenides, and tellurides of zinc and cadmium. The piezoelectric constants for the hexagonal crystals in this group are markedly higher than for the cubic crystals. An elementary model theory applied to these data leads to electric charges on the metal atom increasing from +0.066 e for ZnTe to +0.84 e for CdS. The elastic compliance increases regularly with increasing anion and cation weight, with no break between the cubic and hexagonal crystals. Pyroelectric constants are given for CdS and CdSe. The quality factor of elastic resonances of CdS plates is measured as function of electric conductivity.

An efficient method for the evaluation of coupling coefficients in configuration interaction calculations

1988-04-01

Peter J. Knowles , Hans‐Joachim Werner

First-principles responses of solids to atomic displacements and homogeneous electric fields: Implementation of a conjugate-gradient algorithm

1997-04-15

Xavier Gonze

The changes in density, wave functions, and self-consistent potentials of solids, in response to small atomic displacements or infinitesimal homogeneous electric fields, are considered in the framework of the density-functional … The changes in density, wave functions, and self-consistent potentials of solids, in response to small atomic displacements or infinitesimal homogeneous electric fields, are considered in the framework of the density-functional theory. A variational principle for second-order derivatives of the energy provides a basis for efficient algorithmic approaches to these linear responses, such as the state-by-state conjugate-gradient algorithm presented here in detail. The phase of incommensurate perturbations of periodic systems, that are, like phonons, characterized by some wave vector, can be factorized: the incommensurate problem is mapped on an equivalent one presenting the periodicity of the unperturbed ground state. The singularity of the potential change associated with an homogeneous field is treated by the long-wave method. The efficient implementation of these theoretical ideas using plane waves, separable pseudopotentials, and a nonlinear exchange-correlation core correction is described in detail, as well as other technical issues.

Normal mode determination in crystals

1981-01-01

Denis L. Rousseau , Robert P. Bauman , S. P. S. Porto

Abstract The group theoretical methods by which the symmetries of normal modes in crystals may be determined are outlined, and a series of tables are presented to facilitate rapid determination … Abstract The group theoretical methods by which the symmetries of normal modes in crystals may be determined are outlined, and a series of tables are presented to facilitate rapid determination of the selection rules for vibrational transitions. Emphasis is placed on the method of nuclear site group analysis in which the number of infrared and Raman active modes of each symmetry may be obtained without detailed analysis of the symmetry elements in the crystallographic unit cell or the construction of tables. By using the tables presented here for most cases identification of the crystallographic space group is sufficient information to allow determination of the vibrational mode selection rules by inspection. Several examples are included in which crystals are analyzed by each of the methods.

Determination of Electronic Structure of Molecules from Nuclear Quadrupole Effects

1949-09-01

C. H. Townes , B. P. Dailey

Nuclear quadrupole coupling constants in molecules depend on the nuclear quadrupole moments and the variation in electrostatic field at the nucleus. It is shown that this variation of electric field … Nuclear quadrupole coupling constants in molecules depend on the nuclear quadrupole moments and the variation in electrostatic field at the nucleus. It is shown that this variation of electric field is usually simply related to the molecular electronic structure, being primarily dependent on the way in which valence electrons fill the lowest-energy p-type orbits. Structural information which can consequently be obtained from known quadrupole coupling constants is discussed. Hybridization of the normal covalent bonds of N, Cl, and As with at least 15 percent s character is clearly shown. The alkali halides appear to be almost purely ionic; the quadrupole coupling data allow no more than 3 percent covalent character. In addition to molecular structure, some nuclear quadrupole moments are approximately evaluated by use of the theory developed here.

Solid acids as fuel cell electrolytes

2001-04-01

Sossina M. Haile , Dane A. Boysen , Calum R. I. Chisholm +1 more

First-Order Raman Effect in Wurtzite-Type Crystals

1969-05-15

Carlos Argüello , Denis L. Rousseau , S. P. S. Porto

First-order Raman scattering from BeO, ZnO, ZnS, and CdS, all having the wurtzite structure (${C}_{6v}$), has been investigated. A discussion of the effects of the competition between the long-range electrostatic … First-order Raman scattering from BeO, ZnO, ZnS, and CdS, all having the wurtzite structure (${C}_{6v}$), has been investigated. A discussion of the effects of the competition between the long-range electrostatic forces and the short-range forces due to anisotropy in the interatomic force constants on the vibrational spectrum has been included. A series of scattering diagrams are presented showing the geometrical arrangements necessary to observe all the $k=0$ phonons for this type of crystal structure. In BeO the ${E}_{2}$ mode was resolved from the transverse modes for the first time. The assignments of the ${E}_{2}$ modes in ZnS differ from previous investigations. From absolute intensity measurements, electro-optic coefficients for BeO, ZnO, and CdS were determined.

Reversible Electrical Switching Phenomena in Disordered Structures

1968-11-11

Stanford R. Ovshinsky

A rapid and reversible transition between a highly resistive and conductive state effected by an electric field, which we have observed in various types of disordered semiconducting material, is described … A rapid and reversible transition between a highly resistive and conductive state effected by an electric field, which we have observed in various types of disordered semiconducting material, is described in detail. The switching parameters and chemical composition of a typical material are presented, and microscopic mechanisms for the conduction phenomena are suggested.

Dielectric relaxation in solids

1999-01-01

A.K. Jonscher

This review presents a wide-ranging broad-brush picture of dielectric relaxation in solids, making use of the existence of a `universality' of dielectric response regardless of a wide diversity of materials … This review presents a wide-ranging broad-brush picture of dielectric relaxation in solids, making use of the existence of a `universality' of dielectric response regardless of a wide diversity of materials and structures, with dipolar as well as charge-carrier polarization. The review of the experimental evidence includes extreme examples of highly conducting materials showing strongly dispersive behaviour, low-loss materials with a `flat', frequency-independent susceptibility, dipolar loss peaks etc. The surprising conclusion is that despite the evident complexity of the relaxation processes certain very simple relations prevail and this leads to a better insight into the nature of these processes.

Superexchange interaction and symmetry properties of electron orbitals

1959-07-01

Junjiro Kanamori

Minuit - a system for function minimization and analysis of the parameter errors and correlations

1975-12-01

F. James , M. Roos

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Ionic Thermocurrents in Dielectrics

1966-08-12

C. Bucci , R. Fieschi , G. Guidi

The ionic thermoconductivity (ITC) method, consisting of the study of the thermally activated release of dielectric polarization, is studied in great detail in alkali halide crystals. The (divalent metal ion, … The ionic thermoconductivity (ITC) method, consisting of the study of the thermally activated release of dielectric polarization, is studied in great detail in alkali halide crystals. The (divalent metal ion, cation vacancy) dipoles give rise to an ITC band below 0\ifmmode^\circ\else\textdegree\fi{}C, whose area is proportional to the polarizing field. The activation energy for dipole orientation can be obtained with an accuracy of 0.1%, when there are no overlapping bands. It is shown that the sensitivity of the ITC in detecting small contributions to the polarization (down to 2\ifmmode\times\else\texttimes\fi{}${10}^{15}$ dipoles per ${\mathrm{cm}}^{3}$) or in separating overlapping relaxation processes is greater than that of methods presently employed. The solubility of the impurities can be studied by measuring the ITC of samples subjected to annealing at a fixed temperature. Intense ITC bands appearing in KCl between 280 and 430\ifmmode^\circ\else\textdegree\fi{}K are probably due to contact effects. Measurements on other substances such as quartz, calcite, and Teflon show that by means of a single ITC measurement one obtains a complete qualitative picture of the polarization in a dielectric.

Conformal Invariance, Unitarity, and Critical Exponents in Two Dimensions

1984-04-30

Daniel Friedan , Zongan Qiu , Stephen H. Shenker

Conformal invariance and unitarity severely limit the possible values of critical exponents in two-dimensional systems.Received 31 January 1984DOI:https://doi.org/10.1103/PhysRevLett.52.1575©1984 American Physical Society Conformal invariance and unitarity severely limit the possible values of critical exponents in two-dimensional systems.Received 31 January 1984DOI:https://doi.org/10.1103/PhysRevLett.52.1575©1984 American Physical Society

A family of ferroelectric bismuth compounds

1962-06-01

E. C. Subbarao

Electronic Population Analysis on LCAO-MO Molecular Wave Functions. IV. Bonding and Antibonding in LCAO and Valence-Bond Theories

1955-12-01

Robert S. Mulliken

It is shown that there is a practically one-to-one correspondence between the occurrence, on the one hand, of positive (bonding) and negative (antibonding) overlap populations in LCAO theory and, on … It is shown that there is a practically one-to-one correspondence between the occurrence, on the one hand, of positive (bonding) and negative (antibonding) overlap populations in LCAO theory and, on the other hand, of bonded attractions and nonbonded repulsions in VB (valence-bond) theory. This correspondence is discussed in terms of examples, and is traced for the N2 molecule both for the assumed case of no s–p hybridization, and for the actual case with hybridization. It is pointed out that repulsions between nonbonded atoms in VB theory (including those which give rise to steric hindrance) have their counterpart in negative overlap populations between the same atoms in LCAO theory. The π overlap populations for the various links in 1,3-butadiene are computed by LCAO theory. It is shown how they are affected by conjugation (see Table I) and the results are compared with those of VB theory.

Dynamic disorder in methylammoniumtrihalogenoplumbates (II) observed by millimeter-wave spectroscopy

1987-12-01

A. Poglitsch , D. Weber

The temperature‐dependent structure of crystalline methylammoniumtrihalogenoplumbates (II)—CH3NH+3PbX−3 (X=Cl, Br, I)—as determined by x‐ray diffraction, is compared with measurements of the temperature‐dependent complex permittivity at frequencies of 50–150 GHz. The dielectric … The temperature‐dependent structure of crystalline methylammoniumtrihalogenoplumbates (II)—CH3NH+3PbX−3 (X=Cl, Br, I)—as determined by x‐ray diffraction, is compared with measurements of the temperature‐dependent complex permittivity at frequencies of 50–150 GHz. The dielectric measurements reveal a picosecond relaxation process which corresponds to a dynamic disorder of the methylammonium group in the high‐temperature phases of the trihalogenoplumbates.

Dielectric polarizabilities of ions in oxides and fluorides

1993-01-01

R. D. Shannon

A set of 61 ion polarizabilities has been derived from the dielectric constants of 129 oxides and 25 fluorides using a least squares refinement technique in conjunction with the Clausius–Mosotti … A set of 61 ion polarizabilities has been derived from the dielectric constants of 129 oxides and 25 fluorides using a least squares refinement technique in conjunction with the Clausius–Mosotti equation. These polarizabilities can be used to estimate mean dielectric constants of ‘‘well-behaved’’ compounds. They should be particularly useful in calculation of mean dielectric constants of compounds whose dielectric constants have not been determined. They can also be used as a framework for distinguishing unusual dielectric behavior from normal dielectric behavior where deviations can frequently be attributed to piezo- or ferroelectricity, conductivity (ionic or electronic), ‘‘rattling’’ or ‘‘compressed’’ cations with correspondingly high or low polarizabilities, or the presence of dipolar impurities. Deviations observed from calculated dielectric constants can be used to search for unusual physical behavior.

Variational density-functional perturbation theory for dielectrics and lattice dynamics

2006-04-19

Keith Refson , P. R. Tulip , Stewart J. Clark

The application of variational density functional perturbation theory (DFPT) to lattice dynamics and dielectric properties is discussed within the plane-wave pseudopotential formalism. We derive a method to calculate the linear … The application of variational density functional perturbation theory (DFPT) to lattice dynamics and dielectric properties is discussed within the plane-wave pseudopotential formalism. We derive a method to calculate the linear response of the exchange-correlation potential in the GGA at arbitrary wavevector. We introduce an efficient self-consistent solver based on all-bands conjugate-gradient minimization of the second order energy, and compare the performance of preconditioning schemes. Lattice-dynamical and electronic structure consequences of space-group symmetry are described, particularly their use in reducing the computational effort required. We discuss the implementation in the CASTEP DFT modeling code, and how DFPT calculations may be efficiently performed on parallel computers. We present results on the lattice dynamics and dielectric properties of $\ensuremath{\alpha}$-quartz, the hydrogen bonded crystal $\mathrm{Na}\mathrm{H}{\mathrm{F}}_{2}$ and the liquid-crystal-forming molecule 5CB. Excellent agreement is found between theory and experiment within the GGA.

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Raman spectrum of anatase, TiO2

1978-12-01

T. Ohsaka , Fujio Izumi , Yoshinori Fujiki

Abstract Raman spectra of anatase have been observed in natural and synthetic crystals. Both crystals show the same spectral features. The Raman band occurring at 516 cm −1 at room … Abstract Raman spectra of anatase have been observed in natural and synthetic crystals. Both crystals show the same spectral features. The Raman band occurring at 516 cm −1 at room temperature is split into two peaks centred at 519 cm −1 and 513 cm −1 at low temperature (73 K). The six Raman active fundamentals predicted by group theory are all observed and assigned. The spectra are analyzed by a simple model considering only short‐range forces and the calculated vibrational frequencies are in good agreement with the observed Raman frequencies.

Octahedral Tilting in Perovskites. I. Geometrical Considerations

1997-02-01

Patrick M. Woodward

The 23 Glazer tilt systems describing octahedral tilting in perovskites have been investigated. It is shown that in tilt systems a + a + a − , a + b … The 23 Glazer tilt systems describing octahedral tilting in perovskites have been investigated. It is shown that in tilt systems a + a + a − , a + b + b − , a + a + c − , a + b + c − , a 0 b + b − and a 0 b + c − it is not possible to link together a three-dimensional network of perfectly rigid octahedra. In these tilt systems small distortions of the octahedra must occur. The magnitude of the distortions in the a + a + a − and a 0 b + b − tilt systems are estimated. A table of predicted space groups for ordered perovskites, A 2 MM′ O 6 , for all 23 tilt systems is also given.

The dynamics of charge-density waves

1988-10-01

G. Grüner

In many materials with a highly anisotropic band structure, electron-phonon interactions lead to a novel type of ground state called the charge-density wave. The condensate is pinned to the underlying … In many materials with a highly anisotropic band structure, electron-phonon interactions lead to a novel type of ground state called the charge-density wave. The condensate is pinned to the underlying lattice by impurities and by boundary effects, but can, even for small electric fields, carry current in a fashion originally envisioned by Fr\"ohlich. This review discusses some of the underlying theories and the main experimental observations on this new collective transport phenomenon. The frequency- and electric-field-dependent conductivity, current oscillations, electric-field-dependent transport coefficients and elastic properties, together with nuclear-magnetic-resonance experiments, provide clear evidence for a translational motion of the condensate. Various theories, involving classical and quantum-mechanical concepts, are able to account for a broad variety of experimental findings, which were also made in the presence of combined dc and ac fields.

Conduction in polar crystals. I. Electrolytic conduction in solid salts

1938-01-01

N. F. Mott , M. J. Littleton

N. F. Mott and M. J. Littleton, Trans. Faraday Soc., 1938, 34, 485 DOI: 10.1039/TF9383400485 N. F. Mott and M. J. Littleton, Trans. Faraday Soc., 1938, 34, 485 DOI: 10.1039/TF9383400485

Anomalous paramagnetism of copper acetate

1952-10-09

B. Bleaney , K D Bowers

The paramagnetic resonance spectrum of copper acetate is anomalous in that it resembles that of an ion of spin 1, and its intensity decreases as the temperature is lowered. The … The paramagnetic resonance spectrum of copper acetate is anomalous in that it resembles that of an ion of spin 1, and its intensity decreases as the temperature is lowered. The latter is correlated with the decreasing susceptibility found by Guha (1951). The following hypotheses are suggested: (1) the crystalline field acting on each copper ion is similar to that in other salts such as the Tutton salts; (2) isolated pairs of copper ions interact strongly through exchange forces, each pair forming a lower singlet state and an upper triplet state, the latter only being paramagnetic. On this basis both the fine structure and the hyperfine structure of the spectrum have a simple explanation, and the theory also predicts a small initial splitting of the triplet state of the same order as that found experimentally. The unit cell of the crystal contains two differently oriented pairs of ions, and, using an empirical value for the exchange parameter, fair agreement with the susceptibility measurements of Guha is obtained.

Structure of a ferroelectric and ferroelastic monodomain crystal of the perovskite BiFeO3

1990-12-01

F. Kubel , H. Schmid

A ferroelec. and ferroelastic monodomain single crystal of BiFeO3 at space group R3c is rhombohedral, with a 5.57874(16), c 13.8688(3) .ANG.; arh 5.6343 .ANG., arh 59.348 Deg; d. (calcd.) = … A ferroelec. and ferroelastic monodomain single crystal of BiFeO3 at space group R3c is rhombohedral, with a 5.57874(16), c 13.8688(3) .ANG.; arh 5.6343 .ANG., arh 59.348 Deg; d. (calcd.) = 8.337 for Z = 6. Final R = 2.4, Rw = 1.9% for 422 reflections. The structure can be described as a rhombohedrally distorted simple cubic perovskite cell. The O octahedron is distorted with min. and max. O-O distances of 2.710(7) and 3.015(9) .ANG., resp., and rotated by about +- a = 13.8(3) Deg around the 3-fold axis. The Fe atom is shifted away from the center of the deformed octahedron by .apprx.0.134(7) .ANG. along the 3-fold axis. The Bi atom is shifted with respect to 2 neighboring octahedron centers by .apprx.0.540(7) .ANG. along the 3-fold axis. The ferroelec. poling mechanism was analyzed: atom displacements were calcd. for 60, 120 and 180 Deg switching of Ps and found to be 0.44, 0.62 and 0.82 .ANG. for Fe. Av. oxygen displacements for +a (-a) rotated octahedra were 0.87 (0.89) 1.13 (1.24) and 1.34 (1.53) .ANG.. Av. Bi shifts were <0.06 .ANG.. As the displacements increase in the order 60, 120 and 180 Deg switching of Ps, the 180 Deg reversal must have a very high activation energy and will be avoided.

Ionicity of the Chemical Bond in Crystals

1970-07-01

J. C. Phillips

The nature of the chemical bond in crystals is discussed. The general theories of L. Pauling based on thermochemical data and of C. A. Coulson based on valence bond concepts … The nature of the chemical bond in crystals is discussed. The general theories of L. Pauling based on thermochemical data and of C. A. Coulson based on valence bond concepts are compared with a recent spectroscopic theory. Particular emphasis is placed on binary crystals of formula ${\mathrm{A}}^{N}{\mathrm{B}}^{8\ensuremath{-}N}$ which includes most tetrahedrally coordinated semiconductors as well as crystals of the rocksalt (NaCl) family. A wide range of physical properties is discussed, including crystal structure, energy bands, elastic constants, ionization energies, and impurity states. The role of quantum-mechanical sum rules and spectral moments in constructing simplified models of bond and band behavior is explored. Stress is laid throughout on methods for incorporating quantum-mechanical effects into properties of chemical bonds through algebraic relations rather than through variational solutions of the wave equation.

Macroscopic polarization in crystalline dielectrics: the geometric phase approach

1994-07-01

Raffaele Resta

The macroscopic electric polarization of a crystal is often defined as the dipole of a unit cell. In fact, such a dipole moment is ill defined, and the above definition … The macroscopic electric polarization of a crystal is often defined as the dipole of a unit cell. In fact, such a dipole moment is ill defined, and the above definition is incorrect. Looking more closely, the quantity generally measured is differential polarization, defined with respect to a "reference state" of the same material. Such differential polarizations include either derivatives of the polarization (dielectric permittivity, Born effective charges, piezoelectricity, pyroelectricity) or finite differences (ferroelectricity). On the theoretical side, the differential concept is basic as well. Owing to continuity, a polarization difference is equivalent to a macroscopic current, which is directly accessible to the theory as a bulk property. Polarization is a quantum phenomenon and cannot be treated with a classical model, particularly whenever delocalized valence electrons are present in the dielectric. In a quantum picture, the current is basically a property of the phase of the wave functions, as opposed to the charge, which is a property of their modulus. An elegant and complete theory has recently been developed by King-Smith and Vanderbilt, in which the polarization difference between any two crystal states---in a null electric field---takes the form of a geometric quantum phase. The author gives a comprehensive account of this theory, which is relevant for dealing with transverse-optic phonons, piezoelectricity, and ferroelectricity. Its relation to the established concepts of linear-response theory is also discussed. Within the geometric phase approach, the relevant polarization difference occurs as the circuit integral of a Berry connection (or "vector potential"), while the corresponding curvature (or "magnetic field") provides the macroscopic linear response.

Simple ways of determining perovskite structures

1975-11-01

A. M. Glazer

A simple technique is described for ascertaining trial models for the structures of perovskites. The method relies on an understanding of the fundamental components of the structure. Rules are given … A simple technique is described for ascertaining trial models for the structures of perovskites. The method relies on an understanding of the fundamental components of the structure. Rules are given for determining trial models rapidly.

Infrared and Raman Spectra of Inorganic and Coordination Compounds

1987-06-01

Kenneth R. Seddon

Infrared and raman spectra of inorganic and coordination compounds

1978-08-01

Dietmar Seyferth

Bulk characterization methods for non-centrosymmetric materials: second-harmonic generation, piezoelectricity, pyroelectricity, and ferroelectricity

2006-01-01

Kang Min Ok , Eun Ok , P. Shiv Halasyamani

Characterization methods for bulk non-centrosymmetric compounds are described. These methods include second-harmonic generation, piezoelectricity, pyroelectricity, and ferroelectricity. In this tutorial review with each phenomenon, details are given of the measurement … Characterization methods for bulk non-centrosymmetric compounds are described. These methods include second-harmonic generation, piezoelectricity, pyroelectricity, and ferroelectricity. In this tutorial review with each phenomenon, details are given of the measurement techniques along with a brief history and background. Finally, data interpretation is discussed.

Über die Reaktionsgeschwindigkeit bei der Inversion von Rohrzucker durch Säuren

1889-01-01

Svante Arrhénius

Die Geschwindigkeit der Reaktionen, welche von Elektrolyten (Säuren und Basen) bewirkt werden, steht in einem sehr engen Zusammenhange mit der elektrischen Leitfähigkeit derselben.Aus theoretischen Gründen wurde Proportionalität zwischen diesen beiden … Die Geschwindigkeit der Reaktionen, welche von Elektrolyten (Säuren und Basen) bewirkt werden, steht in einem sehr engen Zusammenhange mit der elektrischen Leitfähigkeit derselben.Aus theoretischen Gründen wurde Proportionalität zwischen diesen beiden Grössen angenommen 1 ), und die nachher ausgeführten experimentellen Bestimmungen 8 ) zeigten, dass dies annähernd der Fall ist.Jedoch konnte diese Beziehung nicht strenge aufrecht erhalten werden.Nachdem man die Möglichkeit gefunden hatte, den

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Medium-size polarized basis sets for high-level correlated calculations of molecular electric properties

1988-01-01

Andrzej J. Sadlej

The basis set polarization approach is applied to the generation of medium-size polarized GTO/CGTO basis sets for accurate calculations of molecular dipole moments and polarizabilities. The polarized basis sets determined … The basis set polarization approach is applied to the generation of medium-size polarized GTO/CGTO basis sets for accurate calculations of molecular dipole moments and polarizabilities. The polarized basis sets determined in this paper for H and C through F are employed in SCF HF and MBPT calculations of dipole moments and polarizabilities of FH, H 2 O, NH 3 , and CH 4 . The excellent results obtained at both the SCF HF and MBPT(4) levels of approximation indicate that the present basis sets can be employed for the accurate high-level correlated studies of relatively large molecules The use of those basis sets in calculations of intermolecular interactions is also discussed.

Electrons in disordered structures

1967-01-01

N. F. Mott

Possible Species of “Ferroelastic” Crystals and of Simultaneously Ferroelectric and Ferroelastic Crystals

1969-08-01

Kêitsirô Aizu

It is convenient to grasp crystals of a kind as “ferroelastic” crystals. They are defined analogously to “ferroelectric” crystals, mechanical strain and stress in the former corresponding to electric polarization … It is convenient to grasp crystals of a kind as “ferroelastic” crystals. They are defined analogously to “ferroelectric” crystals, mechanical strain and stress in the former corresponding to electric polarization and field in the latter respectively. The order of magnitude of the coercive stress for ferroelastic state-shifts which corresponds to the coercive field for ferroelectric state-shifts is expected, on the average, to be 10 2 newt·cm -2 . A determination is made of all theoretically possible species of ferroelastic crystals and the number of states and ferroelectricity or nonferroelctricity in each of these species. It is found that there are 94 of these ferroelastic species and that 42 of them are simultaneously ferroelectric. Incidentally, an alteration is made of the hitherto used symbols for the 88 species of ferroeletric crystals.

Infrared characteristic group frequencies

1981-01-01

Marek Goldstein

The Anomeric Effect and Related Stereoelectronic Effects at Oxygen

1983-01-01

Anthony J. Kirby

Mixed-Anion Inorganic Zn Halide Rb3ZnCl4I

2025-06-25

Ruifeng Liu , Yunluo Wang , Zesen Gao +7 more | Inorganic Chemistry

Lead-free halides, recognized for their nontoxic properties and remarkable stability, have emerged as promising candidates for various optoelectronic applications. In this work, we report the discovery of a novel all-inorganic … Lead-free halides, recognized for their nontoxic properties and remarkable stability, have emerged as promising candidates for various optoelectronic applications. In this work, we report the discovery of a novel all-inorganic zinc halide, Rb3ZnCl4I. With the doping of Mn2+ ion, the as-obtained Rb3Zn1-xMnxCl4I single crystals show intense green photoluminescence with a full width at half-maximum (fwhm) of 52 nm and a peak at 525 nm. The sample with x = 0.30 exhibits the maximum photoluminescence quantum yield (PLQY), reaching a value of 44.14%. We further explored their potential applications in white light-emitting diodes (WLEDs) and X-ray detection. The constructed WLED exhibits a color rendering index (CRI) of 84.1 along with a correlated color temperature (CCT) of 6491 K, demonstrating the material's suitability for high-quality solid-state lighting. Notably, Rb3Zn0.70Mn0.30Cl4I exhibits remarkable stability under X-ray irradiation. Upon being continuously exposed to X-ray irradiation for 10 min at a dose rate of 26.5 Gy/min, the radioluminescence intensity retains 90% of its initial value. This work not only introduces a new member to the family of environmentally friendly and stable lead-free halides but also paves the way for further exploration and development of metal halides in various high-tech fields.

Strain induced anomalous Raman shifting in ferroelectric NbOI <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mn>2</mml:mn></mml:msub></mml:math>

2025-06-25

NULL AUTHOR_ID | Physical review. B./Physical review. B

Evidence for valence-bond pairing in a one-dimensional two-orbital system

2025-06-24

NULL AUTHOR_ID | Physical review. B./Physical review. B

Pressure-Driven Dimensional Transition and Arise of Unconventional Phases in SbCl3

2025-06-24

Fengze Li , Wencheng Lu , Jinqun Cai +3 more | Inorganic Chemistry

At ambient pressure, nitrogen group trihalides predominantly crystallize in molecular configurations. However, under elevated pressures, these compounds undergo pressure-induced structural transitions to two-dimensional (2D) van der Waals layered phases. Despite … At ambient pressure, nitrogen group trihalides predominantly crystallize in molecular configurations. However, under elevated pressures, these compounds undergo pressure-induced structural transitions to two-dimensional (2D) van der Waals layered phases. Despite this, their structural evolution under higher pressure regimes remains poorly characterized, particularly regarding potential dimensional phase crossovers. Here, we present a combined experimental and theoretical study of antimony trichloride (SbCl3) using high-pressure in situ Raman scattering, synchrotron X-ray diffraction, alternating current (AC) impedance, and first-principles calculations. We found that SbCl3 undergoes a phase transition at 12.4 GPa from a molecular phase (Pnma) to an eight-coordinated layered phase (P21/m) at room temperature, which remains stable up to at least 28.9 GPa. Notably, after laser heating to 1900 K at 20.7 GPa, SbCl3 transforms into a noncentrosymmetric three-dimensional (3D) structure (I4̅), featuring a nine-coordinated SbCl9 structural unit. Furthermore, impedance measurements and first-principles calculations, including electronic band structure and electron localization function, were performed and analyzed. Our findings reveal a novel high-pressure phase of nitrogen group trihalides, isostructural to the high-coordinated geometry found in transition-metal phosphides.

Y(HPO4)(NO3)(H2O)·2H2O: A Solvent-Responsive Inorganic Layered Material with Reversible Phase Transitions and Optically Active Proton Conductivity

2025-06-24

Yong‐Seok Heo , Yang Li , Jinjong Kim +2 more | Chemistry of Materials

Resonance parameters of the vector charmoniumlike state <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>G</mml:mi><mml:mo stretchy="false" form="prefix">(</mml:mo><mml:mn>3900</mml:mn><mml:mo stretchy="false" form="postfix">)</mml:mo></mml:mrow></mml:math>

2025-06-23

NULL AUTHOR_ID | Physical review. D/Physical review. D.

Coexistence of topological electronic bands and flat non-contractible phonon nodal lines in Cmce LuS2

2025-06-23

Dexi Shao , Xinyan Lin , Liang Chen +6 more | Science China Physics Mechanics and Astronomy

Suppression of Phase Transition and Dipolar Glassy Behavior in Dimethylammonium/Methylammonium Lead Chloride Single Crystals

2025-06-23

Syed Bilal Junaid , Furqanul Hassan Naqvi , Jae‐Hyeon Ko +5 more | ACS Applied Energy Materials

NEXAFS spectral peculiarities in Sn:SiO2 composite layer

2025-06-23

Владимир Сиваков , Poting Liu , Katharina Freiberg +3 more | Results in Physics

Non-Ohmic behavior in (Bi <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:math> Sb <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mi>x</mml:mi></mml:msub></mml:math> ) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mn>2</mml:mn></mml:msub></mml:math> Te <mml:…

2025-06-20

NULL AUTHOR_ID | Physical review. B./Physical review. B

Unraveling the rare ferroelectric-antiferroelectric transition in the two-dimensional hybrid perovskites (PMA) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mn>2</mml:mn></mml:msub></mml:math> PbBr <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mn>4</mml:mn></mml:msub></mml:math>

2025-06-20

NULL AUTHOR_ID | Physical review. B./Physical review. B

Correction of broadband terahertz electro-optic sampling with GaSe crystals

2025-06-20

K. Ogawa , Natsuki Kanda , Yuta Murotani +3 more | Optics Letters

Solid Ion Conductors under Pressure: In Situ Monitoring of the Tetragonal to Cubic Phase Transition of Na3SbS4 and Na3PS4

2025-06-18

Vasiliki Faka , Martin Lange , Dominik Daisenberger +5 more | ACS Materials Letters

Accurate and Efficient Phonon Calculations in Molecular Crystals via Minimal Molecular Displacements

2025-06-17

Lorenzo Soprani , Andrea Giunchi , Marco Bardini +2 more | Journal of Chemical Theory and Computation

Vibrational dynamics governs the fundamental properties of molecular crystals, shaping their thermodynamics, mechanics, spectroscopy, and transport phenomena. However desirable, the accurate first-principles calculation of solid-state vibrations (i.e. phonons) stands as … Vibrational dynamics governs the fundamental properties of molecular crystals, shaping their thermodynamics, mechanics, spectroscopy, and transport phenomena. However desirable, the accurate first-principles calculation of solid-state vibrations (i.e. phonons) stands as a major computational challenge in molecular crystals characterized by many atoms in the unit cell and by weak intermolecular interactions. Here, we propose a formulation of harmonic lattice dynamics based on a natural basis of molecular coordinates consisting of rigid-body displacements and intramolecular vibrations. This enables a sensible minimal molecular displacement approximation for the calculation of the dynamical matrix, combining isolated molecule calculations with only a small number of expensive crystal supercell calculations, ultimately reducing the computational cost by up to a factor of 10. The comparison with reference calculations demonstrates the quantitative accuracy of our method, especially for the challenging and dispersive low-frequency region for which it is designed. Our method provides an excellent description of the thermodynamic properties and offers a privileged molecular-level insight into the complex phonon band structure of molecular materials.

Influence of γ - radiation on the optical characteristics of germanium coordination compounds

2025-06-14

Ya. I. Lepikh | Molecular Crystals and Liquid Crystals

MOLVIB vs VEDA. Revealing the best program to generate safe and reliable vibrational analysis

2025-06-14

Silvia Antonia Brandán | Chemical Physics Impact

Spontaneous ordering in ultra-large anion size-mismatched BaZr (S1−xOx)3

2025-06-09

Hanzhi Shang , Damien West , Haolei Hui +2 more | Applied Physics Letters

Chalcogenide perovskite semiconductors, with their excellent optical absorption, chemical stability, and lack of toxicity, have emerged as a promising alternative to traditional halide perovskites. Through first-principles density functional theory, we … Chalcogenide perovskite semiconductors, with their excellent optical absorption, chemical stability, and lack of toxicity, have emerged as a promising alternative to traditional halide perovskites. Through first-principles density functional theory, we show that despite the large lattice mismatch between the prototypical BaZrS3 and BaZrO3 chalcogenide perovskites, BaZr(S1−xOx)3 can form low-energy ordered lattices that significantly reduce strain. The bandgap dependence of the resulting ordered compound on x is found to exhibit double Vegard's law behavior, having two distinct linear regions, associated with an underlying distorted or undistorted perovskite structures.

Unconventional Thermal Stability of Domain Framework in Ferroelectric CuInP2S6

2025-06-04

Lei Yang , Yunzhe Zheng , Abliz Mattursun +7 more | ACS Applied Materials & Interfaces

Achieving stable and persistent polarization characteristics in ferroelectric (FE) materials is crucial for fabricating high-density, low-power multifunctional memories. In this study, we conducted a comprehensive investigation of the 2D FE … Achieving stable and persistent polarization characteristics in ferroelectric (FE) materials is crucial for fabricating high-density, low-power multifunctional memories. In this study, we conducted a comprehensive investigation of the 2D FE material CuInP2S6 (CIPS), employing piezoelectric force microscopy (PFM), scanning transmission electron microscopy (STEM), and Raman spectroscopy. By comparing CIPS with and without the nonferroelectric (NFE) phase, we observed unexpected stability of the domain framework at high temperatures. This was evidenced by in situ temperature-dependent PFM measurements and Raman spectra. STEM analysis revealed Cu ion defects and charge accumulation at the FE/NFE interface, which contributed to the thermal stability due to a strong pinning effect. This work highlights the significant positive impact of NFE phases on the thermal stability of FE CIPS, providing insights into the development of controllable FE polarization switching and the potential application of highly reliable and durable multifunctional devices.

Practical Aspects of Zeeman-Perturbed NQR Spectroscopy using an Adjustable Electromagnet

2025-06-03

Alireza Nari , Patrick M. J. Szell , David L. Bryce | Solid State Nuclear Magnetic Resonance

Quadrupolar-perturbed solid-state NMR spectroscopy is a highly useful and well-established method for studying quadrupolar nuclei. This method relies on a high ratio of the Larmor frequency to the quadrupolar frequency … Quadrupolar-perturbed solid-state NMR spectroscopy is a highly useful and well-established method for studying quadrupolar nuclei. This method relies on a high ratio of the Larmor frequency to the quadrupolar frequency and is limited, therefore, by the available magnetic field strengths suitable for NMR, which are on the order of 101 T. Nuclear quadrupole resonance (NQR) provides an approach to studying strongly quadrupolar isotopes, but there are technical challenges associated with measuring high-frequency transitions, and with measuring both the quadrupolar coupling constant, CQ, and asymmetry parameter, η, with good precision. We describe here the technical and practical aspects of a modern implementation of Zeeman-perturbed NQR spectroscopy using an adjustable electromagnet, which overcomes the aforementioned challenges. This approach flips the quadrupolar-perturbed solid-state NMR method upside down, so that the quadrupolar interaction is dominant and the Zeeman interaction is the perturbation. 79Br and 127I Zeeman-perturbed NQR spectra are recorded for some solid bromo- and iodobenzene powders using applied magnetic fields on the order of 10-2 T. Various experimental considerations are discussed, including the optimal magnetic field to be used, the optimization of the coil angle, frequency stepping, the simulation of spectra using an exact diagonalization of the Zeeman-quadrupolar Hamiltonian, and how to ensure high precision in the resulting quadrupolar parameters. As an example, a CQ(127) value of 2077.25 ± 1.49 MHz (with η = 0.114 ± 0.008) is measured for sym-triiodotrifluorobenzene in less than an hour at room temperature. The approach holds promise for studying strongly quadrupolar isotopes in a range of materials and obviates the need for ultrahigh magnetic fields in many situations of interest.

Structural and electro-magnetic properties of Na2O-BaO-Al2O3-P2O5 glasses doped with CdO for sensors and magnetic storage devices.

2025-06-01

K.A. Aly , H.A. Abo-Mosallam , Ebrahim A. Mahdy +1 more | Ceramics International

Investigation of Temperature-Dependent DC conductivity in Optically Active NiSeO4•6H2O Single Crystal

2025-06-01

R. Rajesh , P. C. Haripadmam , Anoop S. Nair +2 more | Journal of Physics Conference Series

Abstract NiSeO 4 •6H 2 O single crystals were grown using the technique of slow evaporation at constant temperature. The green-coloured crystals, with dimensions of 45 mm × 20 mm … Abstract NiSeO 4 •6H 2 O single crystals were grown using the technique of slow evaporation at constant temperature. The green-coloured crystals, with dimensions of 45 mm × 20 mm × 20 mm, took approximately 60 days to form. Thermogravimetric analysis (TGA) was performed within the temperature range of 303-423 K, and the results showed that the NiSeO 4 •6H 2 O crystal undergoes dehydration at 370 K. The measured crystal density of 2.34 g/cm agrees with the reported value of 2.336 g/cm. We measured the DC electrical conductivity along both crystallographic axes and over a wide temperature range. The tests were done at temperatures ranging from 20 to 300 K and 303 to 400 K. The activation energies for NiSeO 4 •6H 2 O were calculated from ln(σ) versus 1000/T plots. At room temperature, the DC conductivity values were on the order of 10 −9 S/cm. Optically active crystals with low conductivity values of the order of 10 −9 S/cm finds wide application in electro-optic modulators where low electrical conductivity in the modulator material offers advantages like reduced energy loss and improved performance, particularly in high-speed applications.

Ferroelectricity and Phase Transition in Sn4X4 (X = O, S, Se) Monolayers

2025-06-01

Dong An , Ruixiang Fei , Lin Hu | The Journal of Physical Chemistry C

Effect of γ-Irradiation on Low-Temperature Hopping Conductivity in InSe Single Crystals Doped by Er

2025-06-01

A. A. Ismayilov , N. Z. Gasanov , P. H. Ismayilova +1 more | Semiconductors

New organic–inorganic bromides[(C3H7)4N]2MBr4 (M=Hg and Cd): Synthesis, crystal structure and vibrational characterization

2025-06-01

M. Khalfa , A. Oueslati , K. Khirouni +4 more | Journal of Alloys and Compounds