Y. C. Venudhar

Phase transition in potassium lithium sulphate

Phase transition and lattice parameter variation with temperature of potassium lithium sulphate have been studied. Precision lattice parameters have been determined at various temperatures, ranging 30°C to 400°C. The diffraction pattern obtained above 435°C differs from that taken at room temperature suggesting a structural change, contrary to the reports of Fischmeister and others.

Thermal expansion anomaly in silver indium selenide at elevated temperatures

Abstract A precise determination of the lattice parameters of silver indium selenide was made in the temperature range 28–478 °C using a 19 cm Unicam high temperature powder camera and Cu Kα radiation. Cohens least-squares method was adopted for determining the lattice parameters at each temperature. The data were used to evaluate the coefficients of thermal expansion, perpendicular ( α ⊥ and parallel ( α ∥ ) to the principal axis, at various temperatures. The parameter a decreases non-linearly with increasing temperature whilst the parameter c increases from room temperature to about 360 °C and then decreases non-linearly. The unit cell volume decreases non-linearly with temperature throughout the temperature range studied. The negative value of α ⊥ increases linearly with increasing temperature; the positive value of α ∥ decreases non-linearly, becomes zero at about 360 °C and above 360 °C it becomes negative and increases numerically with increasing temperature.

X-ray determination of the effect of temperature on the lattice parameters and the coefficients of thermal expansion of palladium-silver-gold alloys

Abstract With a 19 cm Unicam high temperature powder camera, the precision lattice parameters and the coefficients of thermal expansion of three different compositions of Pd-Ag-Au ternary alloys have been studied at various temperatures ranging from room temperature to 899 °C by the X-ray method. It is found that, for all three alloys, the lattice parameter increases with increasing temperature. However, for all three alloys the variation of the coefficient of thermal expansion with temperature is found to be constant within the limits of experimental error. The composition dependence of the lattice parameter was also examined. The lattice parameter increases with decreasing palladium concentration, but shows a negative deviation from Vegards law.

X-ray studies on the thermal expansion of copper indium disulphide

The lattice parameters of the compound copper indium disulphide (CuInS2) have been measured by x-ray diffraction. The data have been used to evaluate the coefficients of thermal expansion, perpendicular and parallel to the principal axis. The thermal expansion studies revealed the anisotropy between the axial expansion coefficients having a larger coefficient of expansion alonga axis than that alongc axis. The anisotropic thermal expansion of this compound is interpreted in terms of the thermal expansion of the Cu-S and In-S bonds.

Anisotropic thermal expansion of copper gallium selenide

Unit-cell parameters for the chalcopyrite type ternary semiconducting compound copper gallium selenide (CuGaSe2) have been determined accurately, using the least-squares method, for reflections in the range of Bragg angles 64-82 degrees , by the X-ray powder diffraction method. A study of the thermal expansion of the chalcopyrite structure unit-cell of the compound, determined over the temperature range 28-685 degrees C, has revealed the anisotropy between the axial expansion coefficients; that for the c axis (24.93*10-6 degrees C-1) is about four times that for the a axis (5.91*10-6 degrees C-1) at 50 degrees C. Anomalous behaviour of the expansion coefficients, similar to that for AgInSe2, AgGaSe2 and AgGaS2, has not been observed for this compound.

Temperature dependence of the lattice parameter and the thermal expansion of AgAu (50 AT.%) alloy by an X-ray method☆

Abstract Using a Unicam high temperature powder camera 19 cm in diameter and Cu Kα radiation, powder photographs of Ag-Au (50 at.%) alloy were taken at various temperatures ranging from room temperature to 900 °C. The precision lattice parameters have been determined from these photographs by Cohens analytical method. The data have been used to evaluate the coefficients of thermal expansion at various temperatures by a graphical method. The expansion coefficient increases linearly with increasing temperature.

Thermal expansion and Debye temperatures of KCl-KBr mixed crystals by an x-ray method

The precision lattice parameters and the coefficients of thermal expansion of KCl, KBr, and their solid solutions have been determined as a function of temperature by an X-ray method using a high-temperature powder camera. From the X-ray diffractograms obtained at room temperature the Debye-Waller factors, Debye temperatures and the root mean square amplitudes of vibration of these mixed crystals have been evaluated. A linear relationship is obtained between the lattice parameter and the composition of the solid solution in accordance with Vegards law. Both of the thermal parameters, the thermal expansion coefficient and the root mean square amplitude of thermal vibration, vary non-linearly with increasing mole percentage of KBr, the deviation from linearity being maximum around equimolar concentration. The composition dependence of these parameters is discussed in relation to a number of physical properties of these mixed crystals available in the literature.

X-ray studies of the thermal expansion and Debye temperatures of Pd-Ag-Au ternary alloys

Using a Unicam high temperature powder camera 19 cm in diameter, the precision lattice parameters and the coefficients of thermal expansion of Pd-Ag-Au ternary alloys of the type Pdx-Ag(1−x)2-Au(1−x)2 have been determined at different temperatures ranging from room temperature to 900 ° by the X-ray method. From the X-ray diffractograms, obtained on a Philips Diffractometer at room temperature, the Debye-Waller factors, Debye temperatures and the root-mean-square amplitudes of thermal vibration of these alloys have been evaluated. The composition dependence of the lattice parameter is examined. The lattice parameter increases with decreasing palladium concentration, but shows a negative deviation from Vegards law as in the case of the binary systems Pd-Ag and Pd-Au. Both the thermal parameters, the thermal expansion coefficient and the r.m.s. amplitude of thermal vibration show a systematic variation with composition and no anomalous character is found as in the case of the hardness data for these alloys. A gradation is observed between the lattice parameter and the mean expansion coefficient on the one hand and between the lattice parameter and the Debye temperature on the other hand.

Lattice thermal expansion of rubidium calcium fluoride

Fluorides of the type AMF3 (where A is K, Rb, T1 or Cs and M is a 3d transition element) crystallize in the perovskite structure. Rubidium calcium fluoride (RbCaFa) has a cubic perovskite type structure (see Fig. 1) at room temperature with the space group Pm3m (0~) [1]. This compound has been of great interest because of its large dielectric constant which gives rise to a host of properties having commercial applications [2]. During the last few years, extensive studies have been made on the experimental and theoretical aspects of structural phase transitions occurring in the compounds of perovskite structure [3, 4]. However, very little information is available about the high temperature lattice thermal behaviour of these compounds. Since these studies are of great importance in the study of a large number of problems involving lattice vibrations and anharmonic effects in solids, it is thought worthwhile to undertake a general programme of studying the lattice thermal behaviour of perovskites at high temperatures. The present note, which is a part of this programme, gives an account of the precise determination of the lattice parameters and the coefficients of thermal expansion of RbCaF3 at different temperatures by an X-ray method. The powder sample of RbCaFa, used in the present investigation, was kindly supplied by Dr M. Miillner of the Institut fiir Kernphysik der J. W. Goethe Universit~it, FRG. The compound was grown by the melt method. The details of the growth and purity of this compound have already been described by Maetz et at [5]. For X-ray powder diffraction studies the powder was passed through a 325 mesh sieve. The specimen was prepared by putting this powder in a 0.05 cm diameter thin-walled quartz capillary. It was found necessary to anneal the powder at about 400 ° C to obtain well resolved sharp lines in the high angle region. Using a Unicam 19 cm high temperature powder camera and CuKa radiation from a PW 1730 Philips X-ray Generator, powder

X-ray studies on the precision lattice parameters and the coefficients of thermal expansion of PdAgAu equiatomic per cent alloy

Abstract Using a Unicam high temperature powder camera 19 cm in diameter and Fe Kα radiation, powder photographs of PdAgAu equiatomic per cent alloy were taken at various temperatures ranging from room temperature to 710 °C. The precision lattice parameters were determined from these photographs by Cohens analytical method. The data were used to evaluate the coefficients of thermal expansion at various temperatures by a graphical method. The lattice parameter increases linearly with increasing temperature. The coefficient of thermal expansion is found to be constant in the temperature range studied within the limits of experimental error.