Electric Characterization of Indium Sesquiselenide Single Crystals

Conductivity, Hall-effect measurements were performed on δ-phase In₂Se₃ single crystals, grown by the Bridgman method over the temperature range 150–428 K, in the directions perpendicular and parallel to the c-axis. The anisotropy of the electrical conductivity and of the Hall coefficient of n-type In₂Se₃ had been investigated. The values of the Hall coefficient and electrical conductivity at room temperature spreads from an order of R_H11 = 1.36 × 10⁴ cm³/coul, σ₁₁ = 4.138 × 10⁻³ Ω⁻¹ cm⁻¹ and R_H = 66.55 × 10⁴ cm³/coul, σ = 0.799 × 10⁻³ Ω⁻¹ cm⁻¹ for parallel and perpendicular to c-axis, respectively. The temperature dependence of Hall mobility and carrier concentration are also studied.     

The growth of HgI2 crystals

The paper presents a system for αHgI₂ crystal growth by the temperature oscillation method. The system has a capability of crystal growing at an excess I₂ or Hg vapour pressure. Optimum conditions for producing crystals up to 2 cm³ by volume have been established. The crystals grown at an excess I₂ vapour pressure have higher resistivity and higher drift electron and hole mobilities — μ_e = 120 cm² V⁻¹ s⁻¹ and μ_h = 6 cm² V⁻¹ s⁻¹, respectively.     

X-Ray Studies of Some Europium Compounds at Elevated Temperatures

The temperature variation of the lattice constants of europium iron garnet (Eu₃Fe₅O₁₂), europium sulphide (EuS) and europium fluoride (EuF₂) has been studied using an X-ray powder diffractometer. The lattice constant of Eu₃Fe₅O₁₂ increases linearly upto 800 °C with an expansion coefficient of 10.4 × 10⁻⁶ °C⁻¹. In the case of EuS, the lattice constant increases non-linearly with temperature. At room temperature the expansion coefficient has a value of 14.3 × 10⁻⁶ °C⁻¹. In EuF₂ the lattice constant increases non-linearly upto 140 °C. At higher temperatures, the lattice constant decreases with increasing temperature with a negative expansion coefficient of −29 × 10⁻⁶ °C⁻¹ over the range 170–235 °C. The cause of the anomalous behaviour observed in EuF₂ is yet to be understood.     

Kinetics of growth of calcite crystals in presence of ammonium ions

The growth of calcite crystals from an aqueous supersaturated solution of initial concentration 0.15 mol m⁻³ containing 10 mol m⁻³ of (NH₄)₂CO₃ has been studied at 298 K. The progress of growth has been followed through determining the composition of the solution by chemical analysis. The crystal growth is controlled by the surface reaction mechanism and satisfies a kinetic equation of the second order with the rate constant 3.7 × 10⁻⁶ m⁴ mol⁻¹ s⁻¹ that is independent on the surface area of the present solid. NH₄⁺ ions do not change the crystal growth mechanism but decrease the growth rate of calcite crystals.     

EPR-spectrum of irradiated potassium dichromate single crystals

EPR-spectra of X-irradiated potassium dichromate crystals are studied at various temperatures from RT to LNT. The most intensive lines are interpreted as due to radicals CrO₄³⁻ (A-lines) and CrO₃⁻ (C-lines), resulting from Cr₂O₇ owing to X-irradiation. Hyperfine structure of C-line, due to interaction of unpaired electron with Cr⁵³ nucleus, occurs at low temperatures, and new unobserved earlier Q-lines appear near-by C-line. The spectrum may be described by usual spin Hamiltonian for S = 1/2 with following parameters: for A-line gz = 1.9841, gy = 1.9685, gx = 1.9592; for C-line gz = 1.9148, gy = 1.9671, gx = 1.9886, |Az| = 30.53 · 10⁻⁴ cm⁻¹, |Ax| = 10.62 · 10⁻⁴ cm⁻¹, |Ay| = 6.62 · 10⁻⁴ cm⁻¹.     

EPR and Optical Absorption Spectra of Cr3+ Ions in Lithium Sulphate Single Crystals

Optical absorption and EPR spectra of Li₂SO₄ · H₂O crystals doped with Cr³⁺ are studied at liquid nitrogen temperature. The bands are found in absorption spectra with maxima about 17000, 23 800 and 37 200 cm⁻¹, assigned to the ⁴A₂ → ⁴T₂, ⁴A₂ → ⁴T₁ and ⁴A₂ → ⁴T₁ (⁴P) transitions, respectively. The crystal field theory parameters were determined and appeared to be as follows: Dq = 1700 cm⁻¹, B = 667 cm⁻¹, C = 3002 cm⁻¹. The lines resulting from Cr³⁺ ions are found in EPR spectra. All lines are doublets, which is indicative of presence of two magnetically unequivalent centre positions, and have the hyperfine structure resulting from interaction of the unpaired electron spin with Cr⁵³ isotope nucleus. Centres are oriented in such a way, that z-axes, corresponding to two centre positions, are situated at both sides of a-axis at an angle of about 3°. Spin Hamiltonian parameters were found as follows: g_x = 1.985, g_y = 1.984, g_z = 1.988, D = 0.130 cm⁻¹, E = 0.016 cm⁻¹, |A| = 17.8 · 10⁻⁴ cm⁻¹.     

Properties and structure of (1 − x)Li2O–xNa2O–Al2O3–4SiO2 glass systems

(1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses were studied for the progressive percentage substitution of Na₂O for Li₂O at the constant mole of Al₂O₃ and SiO₂. The crystallization temperature at the exothermic peak increased from 898 to 939 °C when the Na₂O content increases from 0 to 0.6 mol. The coefficient of thermal expansion and density of these as-quenched glasses increase from 6.54 × 10⁻⁶ °C⁻¹ to 10.1 × 10⁻⁶ °C⁻¹ and 2.378 g cm⁻³ to 2.533 g cm⁻³ when the Na₂O content increases from 0 to 0.4 mol, respectively. The electrical resistivity has a maximum value at Na₂O · (Li₂O + Na₂O)⁻¹ = 0.4. The activation energy of crystallization decreases from 444 to 284 kJ mol⁻¹ when the Na₂O content increased from 0 to 0.4 mol. Moreover, the activation energy increases from 284 kJ mol⁻¹ to 446 kJ mol⁻¹ when the Na₂O content increased from 0.4 to 0.6 mol. The FT-IR spectra show that the symmetric stretching mode of the SiO₄ tetrahedra (1035–1054 cm⁻¹) and AlO₄ octahedra (713–763 cm⁻¹) exhibiting that the network structure is built by SiO₄ tetrahedra and AlO₄.     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Quantum mechanical relations in interface processes at electrode systems of the second kind

It is shown that the difference of the electrochemical standard potentials between Ag/AgCl(s), KCl (aq, a = 1 mole l⁻¹) and Ag/AgBr(s), KBr (aq, a = 1 mole l⁻¹ can be attributed to the ion exchange from the AgCl phase to the AgBr phase. In this process, quantum mechanical relations play an essential part. A relation derived from Einstein's equation for calculating the inner energy of an ionic crystal and from the AC-Josephson equation allows the calculation of the difference of the electrochemical standard potentials between the electrode systems Ag/AgCl(s), Cl⁻-Ag/AgBr(s), Br⁻; Cu/CuCl(s), Cl⁻-Cu/CuBr(s), Br⁻ and Hg/Hg₂Cl₂(s), Cl⁻-Hg/Hg₂Br₂(s), Br⁻ from the frequency of the longitudinal optical phonons. An equation for the quantum mechanical calculation of the nernst factor (RT/zF) in the so-called Nernst equation is given. Thus, the structural parameters of the respective solid state electrodes are in close relation with the transport processes in electrode systems of the second kind.     

Ionic conductvity and NMR investigation of quaternary glasses in the ZrF4BaF2ThF4LiF system

The existence of glasses involving large amounts of LiF (up to 60%) within the ZrF₄BaF₂ThF₄LiF quaternary systems has allowed the authors to study the evolution of transport properties with varying LiF content.A minimum of ionic conductivity bound to a maximum of activation energy has been detected when the atomic Li/F ratio is equal to ≅ 0.07. In the Li-low concentration domain, σ increases regularly and ΔE decreases simultaneously when the BaF₂ concentration increases; on the contrary in the Li-high concentration region log σ and ΔE are quasi-linear functions, increasing and decreasing respectively, of the LiF rate.A ⁷Li and ¹⁹F NMR investigation has shown that Li⁺ and F⁻ ions are simultaneously mobile and the temperature dependence of the number of mobile F⁻ ions has been determined. In the Li-low concentration domain transport properties result from mixed contributions of mobile Li⁺ and F⁻ ions, for high Li concentrations they depends only on the Li⁺ rate.Glasses with high Li-content have good electrical performnces (e.g. σ_175°C ≅ 2.10⁻⁴ω⁻¹ cm⁻¹ for Zr_0.20Ba_0.10Li_0.60Th_0.10F₂).     

The growth of high-quality MCT films by MBE using in-situ ellipsometry

The ellipsometry and RHEED study of high-quality MCT films grown on (112)- and (130) CdTe and GaAs by MBE was carried out. The dependence of the ellipsometric parameter ψ on MCT composition is evaluated. It was shown that such parameters as growth rate, the surface roughness, initial substrate temperature, and film composition may be measured by the in-situ ellipsometry. The appearance of surface roughness was observed in the initial stage of MCT growth under various compositions (x_CdTe = 0 ÷ 0.4). The further growth at optimum conditions leads to the smoothing of the surface and supplies us with high-quality MCT films. The concentration, mobility, and life time of carriers in MCT films were respectively: n = 1.8 × 10¹⁴ ÷ 8.2 × 10¹⁵ cm⁻³, μ_n = 44000 ÷ 370000 cm² V⁻¹ s⁻¹, τ_n = 40 ÷ 220 ns; p = 1.8 × 10¹⁵ ÷ 8.4 × 10¹⁵ cm⁻³, μ_p = 215 ÷ 284 cm² V⁻¹ s⁻¹, τ_p = 12 ÷ 20 ns.     

Hyperfine structure of EPR spectra of Cr5+ ions in irradiated sodium dichromate crystals

EPR spectra are studied of X-irradiated sodium dichromate crystals grown from an aqueous solution by evaporation at 31°C. Doublet lines of EPR-absorption are attributed to the Cr⁵⁺ ions in the CrO₄³⁻ and CrO₃⁻ radicals resulting from radiation decomposition of Cr₂O₇²⁻ and being in the lattice in two unequivalent positions. Hyperfine structure caused by interaction of an unpaired electron with Cr⁵³ nucleus were observed both at liquid nitrogen and room temperatures. For the line, caused by CrO₄³⁻ radical, g_y and A_y directions coincide and angles both between A_x, g_x and A_z, g_z make up ∼ 25°. The spectrum is described by usual spin Hamiltonian for S = 1/2 with following parameters (T = 77 K): for CrO: g_z = 1.984, g_y = 1.970, g_x = 1.961, |A_z| = 8.2 · 10⁻⁴ cm⁻¹, |A_y| = 13.7 × 10⁻⁴ cm⁻¹, |A_x| = 36.1 · 10⁻⁴ cm⁻¹; for CrO₃⁻: g_z = 1.915, g_y = 1.975, g_x = 1.985, |A_z| = 32.2 · 10⁻⁴ cm⁻¹.     

Investigations for Sn diffusion in Pb1−xSnxTe and PbTe

By annealing Pb_1−xSn_xTe and PbTe isothermally in a quartz ampoule Sn diffused from Pb_1−xSn_xTe into PbTe. The profiles obtained have been investigated by means of an electron beam microanalyser, and the coefficients of diffusion have been determined at various temperatures. The diffusion of Sn can be explained by the expressions: D_PbSnTe = 1.5 · 10⁻¹ exp (−1.8 eV/kT) cm² s⁻¹ (0,14 < x < 0,18) D_PbTe = 5,5 · 10⁻⁴ exp (−1.5 eV/kT) cm² s⁻¹. N-type layers are observed at the surface of Pb_1−xSn_xTe specimens.     

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.     

Dilithium dialuminium trisilicate phase obtained using coal bottom ash

The Li₂Al₂Si₃O₁₀ glass-ceramics well crystallized and with a regular morphology was produced starting from a mixture of Li₂CO₃, TiO₂, Al₂O₃ and coal bottom ash, after reducing the magnetite phase content. Its measured thermal expansion coefficient in the temperatures range from 25 °C to 300 °C is α_(25–300) = −23.4 × 10⁻⁷ °C⁻¹. This value is ≈18% smaller than that for the commercial lithium glass-ceramics (−23.4 × 10⁻⁷ °C⁻¹ to 50 × 10⁻⁷ °C⁻¹).     

Structure and electrical resistance of thin scandium films (III). Study on electrical properties

The specific resistance-thickness of ScH_x (vacuum 10⁻⁵ to 5 · 10⁻⁶ Torr) and Sc films (vacuum 1 · 10⁻⁸ to 3 · 10⁻⁸ Torr) relationships have been obtained by keeping a record of a film resistance directly in the course of condensation. The results are discussed according to the theory FUCHS -SONDHEIMER (ScH_x, Sc) and MAYADAS -SHATZKES (Sc) assuming a diffuse scattering of the carriers (P = 0) on the external surface of the films. A mean free path of the current carriers is 188 to 355 Å (T ⋍ 300 K) for ScH_x and 400 Å with grain-boundary scattering parameter from 0.1 to 0.3 for Sc. The temperature dependence of specific resistivity of Sc films was obtained in the interval from 300 to 650 K during the annealing in vacuum 5 · 10⁻⁹ Torr.     

Bestimmung der OH−-Konzentration in LiNbO3-Kristallen durch Protonenresonanz-Untersuchungen

Using calibration samples it was possible to evaluate the concentration of OH⁻-ions in LiNbO₃ crystals from investigations of the nuclear magnetics resonance. The relation between the OH⁻ ion concentration and the absorption coefficient at 2,87 μm was found to be N = (3 ± 1) · 10¹⁹ k (2.87 μm) cm⁻³, which permits a quantitative determination of the OH⁻ content by simple optical absorption measurements.     

Determination of carbon,silicon and boron content in semi-insulating GaAs by infrared absorption spectroscopy

Measurements of the local vibrational mode (LVM) absorption of ¹²C_As at 582 cm⁻¹, ²⁸Si_Ga at 384 cm⁻¹ and ⁽¹⁰⁾¹¹B_Ga at (540 cm⁻¹) 517 cm⁻¹ can be used to determine the concentration of these residual impurities in semi-insulating (SI) GaAs. Although the energy-limited resolution of a grating spectrometer does not allow measuring the line shape of the narrow LVM bands in GaAs the intensity of it determined with definite spectral slit width (SSW) is a reliable measure for the respective impurity content. Calibration factors given in the literature and peculiarities in the measurements and evaluations for the different impurities are discussed.     

Infrared optical properties of Cu1−xLixSe2 thin films

Infrared absorption spectra of Cu_1−xLi_xInSe₂ thin films are measured at room temperature in the wavenumber range from 100 to 600 cm⁻¹. The spectra exhibit two absorption bands in the wavenumber ranges 200–210 cm⁻¹ and 330–355 cm⁻¹ which are ascribed to vibrational modes due to In Se and Li Se vibrations, respectively. The influence of the phase transition from the chalcopyrite structure to the β-NaFeO₂ structure in the composition range x = 0.5–0.6 on the vibrational characteristics is established and discussed.     

Thermoelectric power of indium sesquisulphide single crystals

The investigation covers a temperature range from 200 to 450 K. Thermoelectric power measurements of In₂S₃ crystals showed that all samples under investigation have a positive TEP in all temperature ranges, indicating n-type conductivity for In₂S₃ crystals. The ratio of the electron and hole mobilities is μ_n/μ_p = 4.71. The effective mass of electrons m is found to be 0.00008 × 10⁻³¹ kg. The obtained effective masses of holes m = 1.893 × 10⁻³¹ kg. The diffusion coefficient for both carriers (electrons and holes) is evaluated to be 84.71 cm²/s and 17.985 cm²/s respectively. The mean free time between collision is estimated to be τ_n = 1.7 × 10⁻²⁰s, and τ_p = 8.5 × 10⁻¹⁷s. The estimated diffusion length for electrons is found to be L_n = 1.2 × 10⁻⁹ cm and L_p = 3.9 × 10⁻⁸ cm.