K. V. Krishna Rao

Precision lattice parameters and thermal expansion of calcite

Abstract Precision lattice parameters of calcite have been determined at different temperatures by X-ray method in the temperature range 28° to 524°C using a Unicam 19 cm high temperature powder camera. The data has been used to evaluate the coefficients of thermal expansion, α∥ and α⊥, by a graphical method. Temperature dependence of the coefficients are represented by the following equations: α∥ = 24·670 × 10−6 + 1·742 × 10−8t−5·141 × 10−12t2α⊥ = 3·660 × 10−6 − 7·112 × 10−10t−3·339 × 10−12t2 where t is in °C.

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.

Lattice thermal expansion of silver indium disulphide

Lattice parameters of chalcopyrite type compound silver indium disulphide (AgInS2) were determined as a function of temperature by the x-ray method in the temperature range 28 to 685°C. Using these data, the coefficients of thermal expansion,a⊥ anda‖, were evaluated by a graphical method. The temperature dependence ofa⊥ anda‖ is represented by a suitable equation. The anisotropic thermal expansion of AgInS2 is explained in terms of the thermal expansion of the Ag-S and In-S bonds of the AgInS2 lattice.

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.

Pressure induced phase transition in mercurous chloride

Pressure induced phase transition in mercurous chloride has been studied by high pressure x-ray diamond anvil cell. The change in diffraction pattern started and ended at a pressure of about 5 kbar and 20 kbar respectively. The patterns recorded at 20 kbar could be indexed basing on an orthorhombic lattice, with lattice parametersa=4.23 Å,b=4.54 Å andc=10.44 Å.

TEMPERATURE DEPENDENCE OF THE LATTICE PARAMETERS AND THE THERMAL EXPANSION OF CDCR2X4 (X S, SE)

Abstract A precise X-ray determination of the lattice parameters of the ferro-magnetic chromium chalcogenide spinel compounds CdCr 2 S 4 and CdCr 2 Se 4 was made in the temperature range 28–685 °C using a Unicam 19 cm high temperature powder camera. These data were used to evaluate the coefficients of thermal expansion at various temperatures by a graphical method. The coefficient of thermal expansion increases non-linearly with increasing temperature in both the compounds. The thermal expansion behaviour of these compounds is discussed in relation to their structure and other physical properties.