Thermal expansion in CuAlTe2 compound

The lattice parameters a and c as well as the axial thermal expansion coefficients α ⟂ and α ∥ in the CuAlTe₂ chalcopyrite-type compound are determined as a function of temperature in the range from 80 to 650 K by a X-ray diffractometry technique. The data obtained are used to evaluate the axial ratio c/a, the tetragonal distortion δ = 2 — c/a, the interatomic distances for Cu Te and Al Te bonds and their temperature coefficients. It is found that the thermal expansion behaviour of CuAlTe₂ is similar to that of other CuB^IIIC^VI₂ compounds in having a relatively small expansivity along the c-axis and a large one in the perpendicular direction. When comparing the results for a series of the CuB^IIIC^VI₂ compounds (B Al, Ga, In; C S, Se, Te) it is shown that the correlations between the thermal expansion coefficients α ⟂, α ∥, α_m, dδ/dT and the tetragonal distortion δ, as well as the molar mass of the compound take place.     

Elastic debye temperature of compounds with sphalerite structure

Elastic Debye temperatures θ_EL of the semiconducting compounds A^IIIB^V, A^IIB^VI and CuCl are evaluated from second order elastic constants C_ik available from the literature. The dependence of θ_EL on temperature is given. The results at 0 K are compared with those calculated from low temperature measurements of specific heat. Generally, the agreement between these values is better than found in the literature up to now.     

Interatomic force constants in AIIBIVCV2 chalcopyrite compounds

Force constants of the A^II C^V and B^IV C^V bonds in the A^IIB^IVC^V₂ compounds with chalcopyrite structure are estimated from experimental lattice vibration data using a simplified version of the Keating model. It is shown that the force constants depend exponentially on the bond length. The parameters of this relation are practically the same as those found for the A^IV A^IV, A^III B^V and A^II B^VI bonds in the elemental semiconductors and binary compounds and for the B^III C^VI bond in the A^IB^IIIC^VI₂ semiconductors.     

Heat capacity and lattice anharmonicity in CdBIVC chalcopyrite compounds

The heat capacity at constant pressure of CdSiP₂, CdGeP₂, CdSnP₂ and CdGeAs₂ is measured in the temperature range from 300 to 500 K. The anharmonic contribution to the heat capacity is evaluated and it is shown that the degree of lattice anharmonicity decreases with increasing atomic weight of the constituent atoms of the compounds. Comparing the temperature variation of the heat capacity and of the thermal expansion coefficient some conclusions are made regarding the interatomic potential in the A^IIB^IVC compounds.     

Lattice Vibrations and Interatomic Forces in AIIB2IIIC4VI Defect-Chalcopyrite Compounds (I) Keating Model Considerations

The lattice vibrations of the A^IIB^III₂C^VI₄ semiconductors with defect-chalcopyrite structure are treated in a simplified version of the Keating model considering only interaction with nearest neighbours and assuming that all anions occupy their ideal lattice sites. It is found that in this model the frequencies of the nonpolar and polar modes with highest energy are determined by the properties of the B^III–C^VI sublattice alone. The frequencies of all the other optical modes depend not only on the A^II–C^VI and B^III–C^VI interactions but are also influenced by the presence of the ordered array of vacancies. The results obtained are compared with previous model considerations.     

High-frequency dielectric constant of AIIB2IIIC4VI ordered-vacancy compounds

The mean high-frequency dielectric constant of ZnIn₂Se₄, CdIn₂Se₄, ZnIn₂Te₄ and CdIn₂ Te₄ was determined from unpolarized infrared reflectivity spectra measured in the wavenumber range v̄ = 600 – 4000 cm⁻¹. A simple relation based on the quantum dielectric theory for multibond crystals is proposed to estimate the mean high-frequency dielectric constant of the A^IIB₂^IIIC₄^VI compounds from individual bond susceptibilities. The results of the calculations are compared with existing experimental data, and susceptibilities of the Hg C^VI bonds are estimated.     

Lattice Vibrations and Interatomic Forces in AIIB2IIIC4VI Defect-Chalcopyrite Compounds (II). Analysis of Nonpolar Optical Modes

A simplified version of the Keating model originally derived for defect-chalcopyrite compounds is extended to include all A^IIB₂^IIIC₄^VI compounds with ordered arrays of vacancies. It is shown that the trends and frequencies of the nonpolar optical modes of these compounds can be described within this model. Simple scaling laws for the interatomic force constants are proposed and compared with corresponding relations for other binary and ternary compounds with tetrahedral coordination.     

Infrared and Raman Spectra of ZnIn2Se4

Infrared reflectivity and Raman spectra of polycrystalline ZnIn₂Se₄ revealed a total number of seven structures due to optical vibrational modes. Based on a comparison with previous measurements on other A^IIB₂^IIIC₄^VI compounds a symmetry assignment of the modes is proposed.     

Electrical and optical properties of CuGaTe2

The electrical and optical properties of CuGaTe₂ single crystals were investigated by resistivity and Hall effect measurements in the temperatur range T = 77… 300 K and optical transmission measurements in the temperature range T = 20… 300 K at photon energies hν = 1.15…1.50 eV. All samples were p-type conducting due to shallow acceptors with ionization energies E_A1 ≈︁ 10⁻³ eV and concentrations N_A1 ≈︁ p = (2…4). 10¹⁸ cm⁻³. The absorption spectra could be described by simultaneous consideration of acceptor - to - conduction band transitions with E_A2 = 360 meV and N_A2 ≈︁ 10²² cm⁻³ and valence band - to - conduction band transitions with E_G = 1.24 eV at room temperaure. The temperature coefficient of the fundamental edge is dE_G/dT = −4.0. 10⁻⁴ eV/K. The results are discussed with regard to some general trends found in the Cu-III–VI₂ compounds.     

Comparative infrared lattice vibration study of LiGaO2 and LiInO2 (II). Interatomic force constants

The frequencies of the wurtzite-like modes due to Li–O and Ga–O bond vibrations in LiGaO₂ and of the rocksalt-like mode due to Li–O bond vibrations in LiInO₂ are determined from the infrared reflectivity spectra of the compounds. The force constants for the Li–O and Ga–O bonds in LiGaO₂ follow the same trends as those found for the A^IB^IIIC₂^VI chalcogenides with tetrahedral cordination. The results for LiInO₂ are compared with measurements on the octahedrally coordinated modification of LiAlO₂.     

Investigations of flash evaporated cubIIIC2VI semiconductor thin films by Rutherford backscattering spectroscopy

The chemical composition of CuB^IIIC₂^VI thin films grown by flash evaporation technique was analysed using Rutherford backscattering spectroscopy. The composition of the samples changes with variation of the substrate temperature. In certain temperature ranges nearly stoichiometric layers were obtained.     

Bond Ionicities and Structural Trends in Some LiBIIIC Compounds

The individual and average bond ionicities of LiAlO₂, LiGaO₂, LiInS₂, LiInSe₂ and LiInTe₂ are evaluated from spectroscopic data. It is found that in these compounds the Li C^VI bond is essentially ionic in nature. It is shown that the structural properties of the compounds can be understood in terms of the average bond parameters.     

Über die röntgenographische Analyse der mittleren quadratischen Atomverschiebungen in einigen Halbleiterkristallen

X-ray measurements of the Debye-Waller factor were performed with single crystals of Ge and of semiconducting compounds A^IIIB^V, A^IIB^VI, A^IVB^VI in the temperature range 100 K — 1000 K. From the results the mean square atomic displacements 〈u²〉 and the Debye characteristic temperatures θ of the materials were calculated. Both parameters are discussed with respect to the influence of the temperature, the influence of point defects and, in the case of the compounds, deviations from the stoichiometric composition on the thermal lattice vibrations. Finally, considerations are presented, concerning the relationship between the parameters 〈u²〉 and θ_M, respectively, and the activation energies of vacancy formation and diffusion in the materials.     

Vacancy formation enthalpies in AIBIIIC chalcopyrite semiconductors

Formation enthalpies ΔH_v of single vacancies in all A^IB^IIIC₂^VI chalcopyrite structure compounds are estimated using the macroscopic cavity model. A comparison with atomic sublimation enthalpies ΔH_sub of the B^III and C^VI atoms derived from existing partial vapour pressure data shows that within the accuracy of this data and the theoretical calculations the relation ΔH_v ⪆ ΔH_sub is fulfilled as expected from general considerations.     

Thermal and EPR investigations of thallium gallium disulphide single crystal

In this research, the results of the differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) investigations of TlGaS₂ single crystal are presented. Specific heat capacity (C_p) anomalies of layered TlGaS₂ have been obtained by using a new DSC technique for such crystals. Remarkable heat capacity anomalies have been revealed at the temperatures of 137.7 K, 174.5 K and 238.5 K. It is found that the anomalies appear at maximum with a small deviation (by 3‐4%) from the regular values, and C_p discontinuity amounted to approximately 5%. Additionally, EPR spectra of Fe doped TlGaS₂ single crystals have been recorded at various temperatures down to 6 K for different orientations of the applied magnetic field. Transformations of present EPR spectra are not sufficient for the confirmation of structural phase transitions, in contrast to the cases in iso structural TlInS₂ and TlGaSe₂ compounds. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature dependence of the tetragonal distortion in I–III–VI2 compounds

On the basis of free energy considerations with anharmonic contributions included a model is developed for the temperature dependence of the tetragonal distortion Δ of the I–III–VI₂ compounds. Agreement with experimental data can be only achieved if compounds with Δ < 0.05 and Δ > 0.05 are considered separately. It is suggested that this result is related to the structural order-disorder behaviour of the I–III–VI₂ compounds.     

Heat capacity and thermodynamic properties of LiGaO2 from 180 to 700 K

The heat capacity at constant pressure of LiGaO₂ is measured in the temperature range from 180 to 700 K. An analysis of the experimental data shows that the anharmonic contribution to the heat capacity can be described by a polynomial of fourth order in the temperature. The standard enthalpies and entropies relative to 298.15 K are calculated from the measured heat capacity. Estimates of the standard enthalpy and entropy at 298.15 K are given.     

High-temperature heat capacity,thermodynamic properties and debye temperature of CuGe2P3

The heat capacity at constant pressure of CuGe₂P₃ is measured in the temperature range from 180 to 550 K. Standard enthalpies and entropies relative to 298.15 K are calculated from the heat capacity data. The Debye temperature in the high-temperature limit is estimated to be about 710 K.     

Specific Heat and Lattice Anharmonicity in ZnSiP2 and ZnSiAs2

The molar specific heat at constant pressure was measured for ZnSiP₂ in the temperature range from 300 to 400 K and for ZnSiAs₂ from 300 to 500 K. An analysis of the experimental data showed that the contribution to the specific heat due to lattice anharmonicity can be described by a polynomial of third order in the temperature. Predictions are made regarding the expected temperature dependence of the thermal expansion coefficients and compared with existing experimental data.     

The specific heat capacities of V2O5/P2O5-based glasses

The specific heat capacities of a series of V₂O₅/P₂O₅-based glasses have been measured in the approximate temperature range 3–300 K. The proportions of the host constituents were varied and the effects produced by adding oxides of copper, titanium and sodium were examined. The measurements were extended to investigate the influence of fast neutron irradiation upon the specific heat capacity of pure, initially crystalline V₂O₅.The observations are consistent with a spectrum of background vibrations, the form of which is temperature dependent. At intermediate temperatures the vibrations were consistent with the glasses displaying predominantly chain-like characteristics. With reduction to lower temperatures the vibrational behaviour increasingly resembled that of solids displaying three-dimensional characteristics. The temperature dependence of the specific heat capacity at the lowest temperatures was consistent with the presence of a narrow band of low-frequency modes centred upon 1.67 × 10¹¹ s^?1, the density of which increased with phosphorus content. From observations of the density of these modes in the doped specimens, it was concluded that the role of copper wass largely that of a network former, whereas titanium and sodium were essentially network modifiers.