Defects on TiBiTe2 single crystals

Single crystals of rhombohedral TiBiTe₂ examined by transmission electron microscopy consist of large areas separated by {100}- and {110}-type twins. By measuring the rhombohedral angle from the splitting of diffraction patterns in the twin areas, we calculated the residual strain which remained after the transformation O_h D _3d, ranging from 1.2 to 12.2 %. Dislocations with Burgers vector (a/2) 1¯10 were mobile and the main slip system was (111) 1¯10. Planar defects with complex - fringe contrast were also observed.     

Optical investigation of SnS2 single crystals

The optical properties of the layered compound SnS₂ have been studied. Reflectivity spectra were measured at room temperature, in the energy region 1.8–5.6 eV. Optical transmission measurements were carried out in the temperature range 13–300 K, in order to evaluate the energy gaps and their temperature dependences. The spectra of the optical constantsn, , ₁ and ₂ versus photon energyh have also been presented.     

Optical constants of WSe2 single crystals

The optical constantsn andk for WSe₂ single crystals have been determined from the reflectivity measurements on basal plane of the crystal at wavelengths 5460, 4360 and 4050 Å. From the variation ofk with frequency of radiation, the optical energy band gapE _o of the crystal has been evaluated.     

Growth and characterisation of TaS2 single crystals

Single crystals of tantalum disulphide have been grown by a sublimation or direct vapour transport method. Crystals as large as 15×10×0·05 mm³ grew in the form of platelets and needles above the charge which was kept well distributed within the ampoule. Characterisation of the as-grown crystals has been carried out at room temperature by x-ray diffraction. Electrical conductivity and magnetic susceptibility measurements have also been made.     

Growth and properties of CuInS2 single crystals

CuInS₂ single crystals 14–16 mm in diameter and up to 40 mm in length were grown by the traveling solvent method. The crystals were found to ben-type, with a conductivity of 0.1–10 S/cm, carrier concentration of 10¹⁶–10¹⁷ cm⁻³, and carrier mobility of 150–220 cm²/(V s). The anisotropic thermal expansion of the crystals was measured.     

Photoconductivity of MnIn2S4 single crystals

The spectral response of the photocurrent through MnIn₂S₄ single crystals was measured in the temperature range from 77 to 300 K. A considerable photoresponse was detected in the spectral range from 350 to 900 nm. Slow and fast recombination centers were found in the band gap of MnIn₂S₄     

Growth and characterisation of KNbO2 single crystals

Abstract

The growth of good quality colourless potassium niobate (KNbO₃) single crystals is reported. Various flux compositions with corresponding starting temperatures were chosen from the phase diagram to avoid the black/blue colour formation in growth of KNbO₃ single crystals. Deviation of compositions of colourless and black crystals from the starting composition were analysed by electron spectroscopy for chemical analysis. Dielectric constant and pyroelectric coefficients were calculated with respect to temperature and the transition temperature was confirmed by differential scanning calorimetry studies. Hysteresis loops have been traced with respect to electric field.     

Studies of defects in WSe2 single crystals

A realistic estimation of growth and deformation fault probability has been made in the crystals of WSe₂ grown by a direct vapour transport method. Electron microscopy of the specimens revealed the presence of two-fold ribbons from which theγ/μ ratio has been determined. Attempts to study polytypism have also been described.     

Elastic constants of MoSi2 and WSi2 single crystals

Single crystals of MoSi₂ and WSi₂ with a body-centred-tetragonal C 1 1_b structure were fabricated using a floating-zone method. The elastic wave velocity was measured for samples with various orientations using a simple pulse echo method at room temperature, and six elastic stiffness constantsc _ij were calculated. The stiffness constants were a little higher for WSi₂ than for MoSi₂.c ₁₁ andc ₃₃ of these compounds were approximately equal toc ₁₁ of tungsten and molybdenum, respectively, althoughc _ij (i j) was a little higher for these compounds than for molybdenum and tungsten. Young's modulus 1/s ₁₁ was the highest in the <0 0 1> direction, and the lowest in the <1 0 0> direction. The shear modulus 1/s ₆₆ was high on the {0 0 1} plane and independent of shear direction. It was generally low on the close-packed {1 1 0} plane and largely dependent on shear direction. The elastic constants for the polycrystalline materials were estimated fromc _ij ands _ij . Poisson's ratiov was 0.15 for MoSi₂ and for WSi₂, and these values were much lower than for ordinary metals and alloys. The Debye temperature _D was estimated using the elastic-wave velocity of the polycrystalline materials via the elastic constants such as Young's modulus and shear modulus: it was 759 K for MoSi₂ and 625 K for WSi₂.     

Heat conduction in bismuth-antimony alloy single crystals between 4.2 and 300 K

Thermal conductivity measurements in the temperature range 4.2–300 K on three single crystals of bismuth containing 1.77, 3.2, and 9.33 at % antimony, respectively, are reported. In the low-temperature region, a change from purely phonon-phonon scattering process to a predominantly impurity scattering process was observed with the increase of antimony concentration. In the high-temperature region, the analysis of the results shows the dominance of the electronic contribution over the phonon contribution to the total thermal conductivity, though the latter is not negligible. Individual contributions to total electronic thermal conductivity were calculated, using the equation formulated by Price, for the sample containing 9.33 at % antimony. The agreement between (K _E)_calc and (K _E)_exp = K ? K_L seems to be quite satisfactory up to about 200 K.     

Luminescent properties of Pb2MoO5 single crystals

Lanarkite type Pb₂MoO₅ single crystals were grown using low temperature gradient Czochralski technique and their optical and luminescent properties were studied. The luminescence band at 590–600 nm was observed under UV and X-ray excitations and ascribed to emission of self-trapped excitons. The band is thermally quenched at T > 15 K with the activation energy of process, E_act = 11 meV. The measurements of thermostimulated luminescence demonstrated the presence of shallow traps, which adversely influence the energy transfer to the emission centers.     

Physical properties of BeAl2O4 single crystals

Physical properties of Czochralski-grown single crystal BeAl₂O₄ are reported. Data on hardness, thermal expansion, thermal conductivity, and elastic constants are tabulated as a function of crystallographic orientation. Results indicate that the properties of BeAl₂O₄ compare favourably with those of Al₂O₃.     

Heat capacity of Al-doped V2O3 alloys

Heat capacities of single crystal (Al_xV_1?x)₂O₃ alloys in the composition range 0 < x ≤ 0.10 have been measured in the temperature range 100–740 K. Each of the compositions exhibited a sharp heat capacity maximum lying in the range 170–190 K. With increasing temperature, the transition temperature increases from 171 K (x = 0.0033) to 187 K for x = 0.033 and then steadily decreases to 148 K for x = 0.10. The value of the enthalpy change (δH) increases from 570 cal./mole Al-V₂O₃ for x = 0.0033 to 650 cal./mole Al-V₂O₃ for x = 0.01 and then decreases steadily to 250 cal./mole Al-V₂O₃ for x = 0.10. These transitions have been correlated with the electrical (metal → insulator) transformations occurring in these alloys. The 1 at. % Al-doped V₂O₃ alloys revealed an additional heat capacity anomaly extending over the range 325–370 K. This is identified with the anomalous electrical behavior in this temperature region. The associated δH value was found to be only 30 cal./mole Al-V₂O₃. Analysis of the calorimetric data reveals that the temperature-composition phase diagram for the Al-doped V₂O₃ system is similar to that constructed by McWhan and Remeika (Phys. Rev. $\text{B2}$, 3734, 1970) for the Cr-doped V₂O₃ system.     

High temperature deformation behaviour of MoSi2 and WSi2 single crystals

High temperature deformation behaviour of MoSi₂ and WSi₂ single crystals, which both oriented near 001 and near 100, have been studied by compression tests over the temperature range of 1100 to 1500° C in a high vacuum of less than 6×10^–4 Pa. At elevated temperatures, several per cent compression deformation is possible in both MoSi₂ and WSi₂. Slips on {110 and {013 planes, the dislocation with the direction of Burgers vector 331 and the stacking fault on {110 plane are observed in both deformed MoSi₂ and WSi₂. In MoSi₂, the 0.2% offset stress of the sample oriented <001> is higher than that of the sample oriented <100>. The higher strength of the sample oriented <001> is related to the higher CRSS for the main slip plane of it. The reverse orientation dependence of the strength in WSi₂ is also correlated with the difference in CRSS on {110 and {013 planes, which shows the opposite result to MoSi₂. The higher CRSS on {110 plane in WSi₂ compared to that on {013 may be caused by the formation of a large number of stacking faults on {110 plane.     

Real structure of Cd2Nb2O7 pyrochlore single crystals

X-ray topography and diffractometry are used to study the crystal structure of cadmium pyroniobate Cd₂Nb₂O₇ at room temperature. Structural quality parameters were determined for crystals grown with different degrees of impurity doping. The nature of the crystal lattice damage is analyzed as a function of the type and concentration of impurities. Pis’ma Zh. Tekh. Fiz. 25, 26–33 (July 26, 1999)