Lattice dynamics of ZnGeP2 and AgGaS2 in a tensor-charge model

A tensor-charge model is developed for the lattice dynamics of the ternary compounds A²B⁴C ₂ ⁵ and A¹B³C ₂ ⁶ . The long-wavelength phonon frequencies are calculated for ZnGeP₂ and AgGaS₂ crystals. The tensor-charge parameters are determined by comparing the theoretical and experimental values of the infrared intensities of active frequencies. In the crystal ZnGeP₂, the tensor charges of the zinc and phosphorus are found to be close to the isotropic charges of the point-ion model, while the tensor charge of germanium is very different from the point-ion charge. In the AgGaS₂ crystal, the tensor charges of all the atoms differ appreciably from the point-ion charges. The results are discussed from the point of view of the chemical bond.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 40–44, September, 1980.     

On the lattice dynamics of AgGaS2

Summary The vibrational spectrum and one-phonon density of states of a chalcopyrite crystal AgGaS₂ are calculated in an extended Keating’s model with two-bond-stretching and one-bond-bending force constants. Three charges of ions and three force constants are determined by a least-square fitting to experimental frequencies of long-wave phonons taken from Raman-scattering experiments. The calculated constant-volume specific heat, Debye temperature and elastic constants, of AgGaS₂ are in agreement with the experimental data of other authors.     

Spin lattice coupling coefficients of Co2+ ion in cubic ZnS Crystal

Summary From a uniform and simple method suitable to alld ⁿ ions for the calculation of the spin-lattice coupling coefficientsG ₁₁ andG ₄₄ inT _d symmetry, the analytic expressions ofG ₁₁ andG ₄₄ ford ⁷ ions in this symmetry have been obtained from the high-order perturbation formulae of zero-field splitting in low symmetries based on the weak-field approximation. By using these expressions, the coefficientsG ₁₁ andG ₄₄ for Co²⁺ ion in ZnS crystal have been calculated and the signs of these coefficients are also given. The absolute values of the calculated results show good agreement with the observed values and the signs of these coefficients remain to be verified experimentally. The author of this paper has agreed to not receive the proofs for correction. The project was supported by National Natural Science Foundation of China.     

Microscopic scattering centers in AgGaS2

Summary Microscopic scattering centers in as-grown AgGaS₂ were investigated by optical and scanning electron microscopy. The defects consisted of rectangular platelets lying in the (100) and (010) planes. Their longest dimension (up to 100 μm) was parallel to the [001]-direction. Their shorter dimension was parallel to the [100] and [010] directions, respectively. The scattering centers were usually fractions of a micrometer thick and did not appear to have a different composition than the matrix phase according to results by energy-dispersive analysis. The defects can be eliminated by annealing in Ag₂S or quenching from elevated temperature, which suggests that the defects may themselves consist of a two-phase region, part of which should be Ga₂S₃-rich, where rodlike or platelike second-phase particles are embedded in the matrix. The quantity and the size of this second phase make a definitive compositional analysis difficult. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Effect of Post-Growth Treatments on the ZnGeP2 Single Crystal Optical Properties in THz Range

Russian Physics Journal -     

Account of the nonbinary nature of the ion interaction in lattice dynamics

The real multiparticle Hamiltonian for a solid with a Coulomb interaction between electrons and nuclei is used in the approximation of dynamic independence of the electrons from the ionic and valence shells to obtain an expression for the crystal energy in terms of the ion-ion interaction and the pseudopotential for the interaction of a valence electron with an ion. A correction to the dynamic matrix due to the existence of a three-particle interaction among ions is found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 88–94, September, 1970.     

On Nambu monopole dynamics in a SU(2) lattice Higgs model

It is shown that an SU(2) Higgs model on a lattice is equivalent to the Georgi-Glashow model in the limit of a small coupling constant between the Higgs and gauge fields. It can therefore be concluded that the transition between the confinement and symmetric phases in a 3 + 1 dimensional SU(2) Higgs model at finite temperature is accompanied by condensation of Nambu monopoles. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 9, 577–580 (10 November 1997)     

Shell model lattice dynamics of transition metal oxides

The lattice dynamics of transition metal oxides has been investigated in detail with threebody force shell model which is a successful extension of the shell model and includes the effect of electron shell displacements as well as deformations. The phonon dispersion relations along three principal symmetry directions obtained from this model have been compared with neutron data and found to give better agreement as compared to other models. The complete phonon spectra have also been computed and used to derive the temperature dependence of Debye temperature, and the second-order Raman and infrared spectra. The derived data agree fairly well with the observed ones wherever available.     

Energy-band structure of semiconductors having the chalcopyrite lattice II. MgSiP2, ZnGeP2, ZnSiAs2, and CdSiP2

The pseudopotential method is used to calculate the band structure of MgSiP₂, ZnGeP₂, ZnSiAs₂, and CdSiP₂. The valence band of these compounds is shown to consist of several allowed subbands separated by energy gaps. There are two levels at the top of the valence band, slightly separated in ZnGeP₂ and ZnSiAs₂ and well-separated in MgSiP₂ and CdSiP₂ — in which there is significant tetragonal compression of the lattice. The effective electron masses at the bottom of the conduction band turn out to be anisotropic, with m/m 7–10.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 95–100, June, 1970.     

Influence of Postgrowth Processing Technology on the Laser Induced Damage Threshold of ZnGeP2 Single Crystal

Russian Physics Journal - The laser induced damage thresholds of ZnGeP2 single crystals are determined. The values of the thresholds under the action of laser radiation at a wavelength of 2,097...     

Three body force model for lattice dynamics of copper

Phonon frequencies of copper are calculated in both symmetry and certain off-symmetry directions using a five parameter three body force model. The validity of the model is shown by a direct comparison with the recent measurements of the off-symmetry phonon frequencies.     

Static displaced shell model for the lattice dynamics of CoCl2

The phonon dispersion curves of CoCl₂ are calculated using the static-displaced-shell model. Good fit to experiment is achieved and a reasonable value for the static intra-ionic polarization of the chlorine ion is obtained.     

CuA1S2 crystalline lattice dynamics

Using the model of rigid ions bound by short-distance forces the lattice dynamics of the CuA1S₂ crystal with chalcopyrites structure are investigated. The model parameters are determined from experiments on infrared reflection and combination scattering of light. The phonon spectrum is calculated in the center of the Brillouin zone and in directions of high symmetry. Oscillator amplitudes for frequencies active in IR reflection and components of the static dielectric permeability tensor are calculated.     

Electrical and optical properties of electron-irradiated ZnGeP2

Conclusions and summary The following conclusions are drawn from the reported study:The electrophysical properties of ZnGeP₂ crystals and their optical transparency in the range hG are attributable to the presence of a density-dominant (10¹⁷–10¹⁹ cm^–3) deep [E_v+(0.5–0.6) eV] growth defect associated predominantly with Zn vacancy clusters.Irradiation by high-energy electrons induces a shift of the Fermi level in the direction of E_G/2 and increases the resistivity of ZnGeP₂ to values of approximately 10¹² ·cm at 300 K. Irradiation with high-energy electrons is an effective technique for the optical bleaching of p-ZnGeP₂. The reversible modification of the optical absorption spectra of p-ZnGeP₂ in connection with irradiation and subsequent annealing indicates that the absorption step in the vicinity of h 0.6 eV is not attributable to light absorption by germanium inclusions, but to optical transition from the valence band to the growth-defect level E_v+(0.5–0.6) eV.Enhancement of the optical transmissivity of p-ZnGeP₂ in the range hG can be achieved in two wayss 1) as the result of a decrease in the density of centers with the level E_v+0.6 eV by variation of the growth conditions or subsequent annealing; 2) by shifting the Fermi level above the energy position E_v+0.6 eV through the irradiation-induced injection of compensating donor centers.The injection of radiation defects is an effective technique for controlling the electrical and optical parameters of the compound ZnGeP₂.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 122–130, August, 1986.