K. Satyanarayana Murthy

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.

The high-temperature thermal expansion of Ni3Al measured by X-ray diffraction and dilation methods

The lattice parameters of Ni3Al have been determined accurately for the temperature range 25 to 594 degrees C by a high-temperature X-ray powder diffraction method. These data are used to evaluate the coefficients of thermal expansion at various temperatures. The thermal expansion of Ni3Al has also been measured from 25 to 1000 degrees C by a dilation method. The thermal expansion values obtained by the dilation method are in good agreement with those determined by the X-ray diffraction method at around room temperature, but the agreement deteriorates with increase in temperature.

Temperature behaviour of the tetragonal distortion and thermal expansion of Cu-III-VI2 chalcopyrite semiconductors

Abstract The tetragonal unit cell parameters a and c of Cu-III-VI2 chalcopyrite semiconductors have been accurately determined at various temperatures in the range from 300 K to about 950 K by X-ray diffractometry. These data were used to evaluate the tetragonal distortion Δ (= 2− c a ) and the linear thermal expansion coefficients αa and αc of the lattice parameters a and c respectively at various temperatures. The lattice constant ratio c a decreases with increasing temperature, resulting in an increase in the tetragonal distortion Δ with temperature. Because of the axial symmetry of these compounds the linear thermal expansivities αa and αc are thermally anisotropic (αa >αc), and this anisotropy increases with decreasing lattice constant ratio c a . The increase in the tetragonal distortion with temperature and the anisotropic thermal expansion of Cu-III-VI2 compounds is explained in terms of the thermal expansion of the Cu-VI and III-VI bonds, taking into account both the covalent and the ionic forces. Some general trends in the temperature dependence of the tetragonal distortion, the order-disorder behaviour and the thermal expansion of these compounds which are indicated by the experimental observations are discussed.

High temperature lattice parameters and thermal expansion of Y1−xCexAl2 (x = 0,0.15, 1) intermetallics

Abstract Precise determination of the lattice parameters of the quasi-binary compounds Y 1− x Ce x Al 2 was made from room temperature to about 800 K using a Unicam (diameter, 19 cm) high temperature powder camera and Cu Kα radiation. The coefficients of thermal expansion at different temperatures were evaluated by an analytical method. It was observed that the lattice parameter increased non-linearly with increasing temperature, whereas the coefficient of thermal expansion decreased with increasing temperature in these compounds. This result is similar to that observed in many of the isotypic RAl 2 intermetallics.

X-ray studies of the thermal expansion of CeAl2 and HoAl2

Abstract A precise determination of the lattice parameters of the rare earth Laves phase compounds CeAl 2 and HoAl 2 was made in the temperature range 30–670°C using a Unicam 19 cm high temperature powder camera and Cu Kα radiation. The data were used to evaluate the coefficient of thermal expansion at various temperatures by an analytical method. It was found that the lattice parameter increases while the coefficient of expansion decreases with increasing temperature in both compounds.

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.

Anisotropic thermal expansivity of the chalcopyrite AgInTe2

Accurate lattice parameters of the tetragonal chalcopyrite semiconductor silver indium telluride (AgInTe2) have been measured by the X-ray powder diffraction method in the temperature range from 300 to 667K. The data have been used to evaluate the axial thermal expansion coefficients alpha a and alpha c at various temperatures. The thermal expansion studies revealed anisotropy between the axial thermal expansion coefficients, with a larger coefficient of expansion along the a-axis than along the c-axis. The principal axial thermal expansion coefficients alpha a and alpha c increase linearly with temperature, gradually approaching 15.40*10-6K-1 for the a and 1.54*10-6K-1 for the c-axis from values at 300K of 9.49*10-6K-1 and 0.69*10-6K-1, respectively. These results are discussed in terms of the thermal expansion of the two types of bonds (Ag-Te and In-Te) and the principal Gruneisen parameters of the chalcopyrite structure of AgInTe2. The temperature dependence of axial ratio (c/a) has been examined.

High temperature thermal expansion characteristics of Ni3Al alloys

The thermal expansion of Ni3Al alloys with and without ternary additions have been investigated with the aid of a dilatometer. The Ni3Al alloys were studied over the temperature range 25–1000 °C. The coefficient of thermal expansion α of all the aluminides studied in this investigation varies linearly with the temperature. The coefficient of thermal expansion of Ni3Al is found to show an increase with the decrease in Al content from stoichiometric composition. B and Zr additions decrease the value α of Ni3Al alloys at room temperature while Hf and Ti additions do not alter it significantly.

X-ray study of the thermal expansion anisotropy in YVO4 and YAsO4 compounds

Abstract The lattice parameters a and c of the zircon-type tetragonal YVO 4 and YAsO 4 are measured in the temperature range from 300 to about 900 K by an X-ray powder diffraction method. The data have been used to evaluate the coefficients of thermal expansion, perpendicular (α⊥) and parallel (α‖) to the principal axis. It is found that for the two compounds almost over the whole investigated temperature range the coefficient of expansion α⊥ is much smaller than that in the parallel direction (α‖). The temperature dependence of α‖ for YVO 4 is unusual, for it decreases 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.