Magnetic and electric properties of the ternary alloys AB

The results of experimental studies of the electrophysical and magnetic properties of solid solutions based on the AB compounds with anion (Zn₃(P_xAs_1−x)₂ and cation (Zn_xCd_1−x)₃ P₂ substitution are reported. The Zn₃(As_xP_1−x)₂ solid solutions are characterized by p-type conductivity (∼ 10¹⁵  10¹⁷ cm⁻³), low Hall mobility and conductivity of ∼ 10⁻² — 10⁻³ ohm⁻¹ cm⁻¹. In the (Zn_xCd_1−x)₃P₂ solid solutions the samples rich in zinc are p-type, those rich in cadmium — n-type, the carrier concentration is ∼ 10¹⁶ — 10¹⁸ cm⁻³. From the measurements of the magnetic properties of the above mentioned alloys it is shown that in the investigated solid solutions a transition from the structure with direct optical transition to those with indirect optical transition occurs.     

Absorption and ionic conductivity of oxygen-containing SrF2 crystals

An absorption band at 3644 cm⁻¹ is caused by isolated OH⁻ ions. O⁻ ions cause an absorption band at 213 nm the oscillator strength of which is 0.020. Charge-compensation of O⁻ ions is effected by F⁻ ion vacancies (F). As for CaF₂ crystals there occur monomers and dimers of [O⁻ – F] complexes. The mass action constants of association of F with oxygen centres are K_AD = ⅓ exp (4.28 – 0.82 eV/kT) for [O⁻ – F], K_AT = 4 exp (17.4 – 1.25 eV/kT) for [2 O⁻ – F] and K_AQ = exp (4.2 – 0.89 eV/kT) for [2 O⁻ – 2 F].     

Density and mobility of anti-frenkel defects in SrF2 crystals

By fitting the theoretically calculated temperature-dependent conductivity σ to the measured dependencies log σT ÷ 1/T the following parameters have been determined: free formation enthalpy of anti-Frenkel defects g_AF = 2.05 eV – 6.35 kT; mobilities of F⁻ion vacancies F and interstitials F: v_νT = 600 exp (-0.70 eV/kT) cm² K/Vs, v_iT = 1.1 · 10⁴ exp (-0.93 eV/kT) cm² K/Vs. — The free association enthalpies of complexes consisting of single foreign ions (Sc³⁺, Y³⁺, La³⁺, Sm³⁺, Li⁺, K⁺, Na⁺, O⁻) and the charge-compensating defect were obtained. The vibration frequency of F⁻ ions in the neighbourhood of F and F is changed by a factor of 2.6 and 0.6, respectively.     

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.     

Thermoelectric properties of indium sesquiselenide single crystals

Single crystals of δ-In₂Se₃ were prepared in the solid state laboratory at Qena-Egypt, by means of Bridgman technique. The temperature dependence of the thermal e.m.f. α in the temperature range from 205 K up to 360 K of In₂Se₃ was studied. The δ-phase In₂Se₃ sample appeared to be n-type. The ratio of the electron and hole mobilities are found to be μ_n/μ_p = 1.378. The effective masses of charge carriers are m = 1.3 × 10⁻³⁰, m = 8.27 × 10⁻³¹ kg for holes and electrons, respectively. The diffusion coefficient was estimated to be D_n = 3.37 cm²/s and D_p = 2.45 cm²/s for both electrons and holes, respectively. The mean free time between collision can be deduced to be τ_n = 70 × 10⁻¹⁶ s and τ_p = 8 × 10⁻¹⁴ s for both electrons and holes. The diffusion length of the electrons and holes are found to be L_n = 1.5 × 10⁻⁷ cm and L_p = 4.4 × 10⁻⁷ cm.     

On the mechanism of chemical polishing of GaAs crystals

In order to establish reproducible conditions for chemical lap polishing of GaAs with NaOCl solutions, containing also OH⁻- and CO -ions, the mechanism of dissolution was investigated using the rotating disk arrangement. In solutions with excess OCl⁻ concentrations likewise diffusion and a reaction of the first order with respect to OH⁻ and CO, complexing agents for Ga-ions, control the dissolution rate, and the surfaces of the wafers are polished. OH⁻ and CO₃^2– concentrations in excess with respect to OCl⁻ lead to rate determining OCl⁻ diffusion and to irregularly polished or film covered surfaces. Diffusion constants for OH⁻, CO and OCl⁻ are given.     

Crystallization and Thermoelectric Power of Tl2Te3 Single Crystals

Thermoelectric power (TEP) of Tl₂Te₃ was measured in the temperature range from 150 to 480 K. The crystal was found to have a p-type conductivity throughout the whole range of temperature. The effective masses of holes and electrons were determined at room temperature and found to be m = 1.1 × 10⁻³⁴ kg and m = 1.72 × 10⁻³⁵ kg, respectively. Also at the same temperature the mobility μ_p was found to be 1737.8 cm²/V.s and μ_n was 3962.2 cm²/V.s. The hole and electron diffusion coefficients were obtained as 44.84 cm²/s, and 102.23 cm²/s. The relaxation times for holes and electrons were calculated and yielded the values τ_p = 1.19 × 10¹² s and τ_n = 4.25 × 10¹³ s, respectively.     

Strukturelle Umklapp-Vorgänge in metastabilen β1-Kupfer-Zink-Mischkristallen bei tiefen und höheren Temperaturen (I). Gitterdynamische Skizze1)

The quantity of the shear-modulus G′ = (c₁₁ – c₁₂)/2 is a measure for the probability of structural Umklapp-processes to occur in metastable β₁-Cu-Zn-solid solutions. Such processes take place, if G′ = G′(T, x) would fall below a critical limit, G′_crit, e.g. by lowering of temperature T or/and Zn-concentration x, because the Fermi-contribution to G′will sink in the 1^st and with him additional the Coulomb-contribution in te 2^nd case. Both ones are the authoritative stabilizing factors for β₁ and therefore specific fo its lattice-dynamical behaviour, especially in the longwavy range of thermoacoustic lattice-vibrations, by which the cooperative Umklapp-motion will escape. Umklapping can also be initiated by favourably oriented dislocations, is G′ would approach to G′_crit in their neighbourhood: G′_critG′(xM8), with xM8  Umklapp-concentration. This is possible by variation of x during isothermal reactions, in the course of whicht he β₁-matrix will heterogenize itself into Zn-poorer and -richer districts β and β (pre-diffusion by means of quenchy vacancies). Both kinds of districts, among which the latter ones will enhance their degree of stability, are joint together coherently. They build up a so called β /β -parquet. The parquet-bricks can reach a critical size, which is necessary that sufficient large atom-collectives can simultaneously be caused to an Umklapp-motion and to occupate new equilibrium positions by thermo-acoustic shear-waves (comparison with a sin-wave beeing changed to a zigzag-line). Only at higher temperatures the bricks come up to the critical size. Umklapping comes about only in the β -bricks, which turn by it to a transition lattice (β₂) with a structure similary to that of the lowtemperature-martensite β′′. After that β₂ changes to α-phase. The way β ⇒ α is marked by the following steps: prediffusion, Umklapping + dislocation, leading to β₂, and a further dislocation dissoziation, leading the atoms to the equilibrium positions in the α-lattice. The so stepped mechanism acts an nucleationmechanism of the α-phase. After the nucleation the α-nuclei grow at the cost of too much formed β (postdiffusion). By isothermal reactions at too low temperatures a mini-herterogenized state of the β₁-matrix will be caused comparable with coldhardening states of other alloys (Guinier-Preston-zones). A β₁-matrix in such a state is unable to isothermal Umklapping, so that α-crystals can be formed – provided that the mini-heterogenities are resolved by increasing of the reaction temperature.     

Dependence of the Electric Properties and the Positron Lifetimes on the Dopant Content in La-doped SrTiO3

The resistivity, the dielectric constant, and the positron lifetimes in La-doped SrTiO₃ have been measured for La content x of 0—10 at.%. It was found that with increasing x, the variations of the resistivity and the dielectric constant and the positron lifetime parameters are nonmonotonic. The positron experiments have shown that the La-doping induces mainly formation of Sr vacancies and variation of Sr vacancy configuration; the most probable configuration is the isolated Sr vacancies (V) as x < 0.5 at.%, the associated defects (La V) for 0.5 < x < 1 at.%, and the associated defects (2 La V) above x = 1 at.%. The results suggest that the variation of the resistivity can be regarded as variation of electron density, and the variation of the dielectric constant results mainly from variations of the space-charge polarizaion and Sr-vacancy concentration and configuration.     

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.     

Non-Arrthenius Behaviour and Divacancy Contribution in Self-Diffusion of 64Cu in Cu

The self-diffusion of ⁶⁴Cu in Cu was investigated in the high temperature range (1078 to 1348 K), applying the tracer-standard sectioning technique. For the frequency factor D₀ and the activation energy Q₀ we found D₀ = (0.68)cm² · s⁻¹ and Q₀ = (2.17 ± 0.02) eV. A slight bending of the Arrhenius plot suggests a divacancy contribution to the self-diffusion of copper. Data sets used in an numerical analysis are in good accord with published results.     

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.     

Hyperfine structure of Cr5+ EPR spectra in X-irradiated potassium halide crystals doped with CrO and Ca2+

The hyperfine structure has been investigated in the EPR spectra of X-irradiated KCl: CrO, Ca²⁺ and KBr: CrO, Ca²⁺ crystals. Preliminarily spectra were simplified by means of heating the crystals up to 400 K for KCl and 440 K for KBr, that destroys the less stable CrO · V centers. It is ascertained, that principal directions of g- and A-tensors do not coincide, and principal A-values are determined. Calculations, making use of the experimental meanings of g- and A-tensor components, showed, that the degree of distortion of oxygen tetrahedra in CrO · Ca²⁺ · V centers is almost the same in both KCl and KBr crystals; besides, these calculations suggest the existence of a strong covalent bonding between the central Cr⁵⁺ ion and four oxygen ligands in CrO ions.     

Defect studies in CuBIIIC chalcopyrite compounds using the ion channeling technique

Based on simple approximations the backscattering minimum yield is estimated for axial ion channeling in perfect crystals of six CuB^IIIC chalcopyrite compounds. The results obtained for CuInSe₂ are compared with experimental channeling spectra. Point defect concentrations up to about 10²¹ cm⁻³ are estimated for CuInSe₂ single crystals grown by the vertical Bridgman method. A simple power law is found for the fluence dependence of the damage density in oxygen implanted CuInSe₂ single crystals.     

Lattice Thermal Expansion in CuGaT2 and CuInTe2 Compounds over the Temperature Range 80 to 650 K from X-ray Diffracion Data

The lattice parameters a and c as well as the thermal expansion coefficients α⟂ and α∥ in the two principal direction for CuGaTe2 and CuInTe 2 chalcopyrite-type compounds have been determined as a function of temperature in the range from 80 to 650 K by the X-ray diffraction method. It is found for both the compounds the coefficient of expansion along the α axis (α⟂) is larger than that along the c axis (α∥) over the whole investigated tem-perature range. When comparing the results for a series of the CuB^IIIC compounds (B Ga, In; C S, Se, Te) it is shown that the thermal expansion anisotropy increases strongly when the Ga atom replaces the In atom while it changes a little when the Te atom replaces the Se atom or the S atom.     

The influence of the direct quench and indirect quench to Ta > Th on the decomposition behaviour of an Al-2 at.% Zn-1 at.% Mg alloy

The decomposition behaviour of an Al-2.0 at.% Zn-1.0 at.% Mg alloy after direct quench (DQ) and indirect quench (IQ:T = 23 °C, t) to the ageing temperature T = 160 °C (above the temperature of the rapid homogeneous nucleation, T_h) was investigated by means of TEM and isothermal resistivity measurements. The precipitation density of the η-particles yields a maximum value at pre-ageing times about 10 min at T = 23 °C. To clear up the reason for that phenomenon a loop-formation and clustering model was introduced.     

Stability Determinant of Anisotropic Phases

The thermodynamic stability of crystal determinant D) and nonstability D_{n st}⁽¹⁴) of the fourteenth order, their adiabatic and corresponding isodynamical coefficients are discussed.     

Stoichiometry and point defects in lithium niobate crystals

Investigations of the OH⁻ ion incorporation into LiNbO₃ crystals and the comparison of calculated and measured densities show that undoped congruent lithium niobate crystals contain Li⁺ and O^{− −} ion vavancies O and Li⁺. If really present, stacking faults are of inferior importance. The good agreement of the absorption edges of stoichiometric and of 2.7 mol% MgO containing congruent lithium niobate crystals is explained by the occupance of all oxygen sites within these crystals.     

Thermal expansion anisotropy and individual bond expansion coefficients in ternary chalcopyrite compounds

The individual bond expansion coefficients of the A^IIB^IVC and A^IB^IIIC₂^VI chalcopyrite compounds are calculated from the principal linear thermal expansion coefficients of the lattice parameters using the regular B C tetrahedron model and a model with a temperature independent free parameter of the lattice. It is shown that the bond expansion coefficients derived from the latter model are in better agreement with the trends found for the interatomic forces in the chalcopyrite compounds and observed for the thermal expansion coefficients in the binary AC, A^IIC and BC compounds.     

Surface preparation of AB semiconductors (Cd3As2, Zn3As2, Cd3P2, Zn3P2) under ultra-high vacuum conditions

The UHV surface preparation of AB materials (crystals and thin films) has been monitored with XPS and AES. Clean and stoichiometric surfaces of AB crystals were prepared by means of low energy ion bombardment and subsequent low temperature annealing. Stoichiometric Cd₃As₂ and Zn₃P₂ thin films with very low amounts of C and O were deposited by the evaporation of bulk material in the UHV. The quality of prepared AB crystal and thin film surfaces was sufficient to carry out density of states investigations (UPS, RELS) with success.