Showing papers by "V. R. K. Murthy published in 1999"

Structural Study on Ca0.6Sr0.4ZrO3

Abstract: Structural study on the compound Ca0.6Sr0.4ZrO3 has been carried out. The study reveals that it is not isomorphous with its parent compounds CaZrO3 and SrZrO3. It belongs to the space group Pmcn and the size of the unit cell is 2ap×√ 2bp×2√ 2cp. The tilt system of the BO6 octahedra is found to be compound and the octahedra are highly distorted. The A-ions are displaced along the [001] direction by about 0.134 A and the displacements in adjacent layers are in the opposite directions.

Structural investigations on the (Ba,Sr)(Zr,Ti)O3 system

Abstract: Structural investigations of the compounds in the series Ba0.27Sr0.73ZryTi1-yO3 have been carried out. The crystal structure goes to lower symmetry with increasing Zr content and the tolerance factor decreases. The variation of Va/Vb is linear with the tolerance factor. The tilt system is a-a-c0 for compositions with y = 0.50 and 0.65. The tilt system is a-a-c+ for compositions with y = 0.80, 0.90 and 0.97 and for BSZT (Ba0.29Sr0.71Zr0.97Ti0.03O3) and BSZTTa (Ba0.29Sr0.71Zr0.95Ti0.04Ta0.01O3). The tilt angle with respect to the pseudocubic [100] and [001] directions increases with the Zr content. For compositions with y = 0, 0.25 and 0.40, the coordination of the A ion (Ba or Sr) is 12, whereas the A-ion coordination number is 11 for compounds with y = 0.50 and 0.65 and it is lower for compositions with y = 0.80, 0.90 and 0.97 and for the compounds BSZT and BSZTTa. The decrease in coordination number indicates that the compounds are becoming more and more covalent with increasing Zr content. A graph of |90°-pc| against the tolerance factor shows that |90°-pc| falls sharply at a tolerance factor corresponding to the compositions used in the fabrication of dielectric resonators. TCf values show that the sign of this parameter changes at a tolerance factor near 0.965 and has a minimum for compounds with orthorhombic Pbnm/Pnma structures.

Coefficient of Volume Expansion and Thermoacoustic Parameters of Alkyl‐Cyano‐Biphenyl Liquid Crystals

Abstract: Dilatometric studies were performed on the nematic and isotropic phases of the homologous series of alkyl-cyano-biphenyl liquid crystals CnH2n+1C6H4C6H4. CN for n = 5 to 9. From these studies the coefficient of volume expansion (a) of the liquid crystal is estimated. Using this data a number of thermoacoustic and an harmonic parameters of the liquid crystal are evaluated. The temperature dependence of these parameters have also been investigated. All these thermoacoustic and an harmonic parameters evaluated in this case show characteristic change in the immediate vicinity of the phase transition temperature.