R. Ilangovan

Preparation, morphology and X-ray diffraction studies on barium strontium titanate single crystals

Abstract Single crystals of BaSrTiO 3 have been grown by flux technique using KF as the flux. Morphology variation with Sr content and their growth conditions have also been investigated. Growth mechanism of the grown crystals is discussed with the help of micromorphologies observed on the habit faces. X-ray diffraction studies on the crushed crystals with 5 mole % to 20 mole % show tetragonal structure and for 30 mole % it shows cubic at room temperature. Ferroelectric hysteresis loops have been traced for asgrown crystals.

Single-crystal neutron diffraction study of the structural phase transition in

The tetragonal-to-cubic transition in ferroelectric (BCT) has been studied using a single-crystal neutron diffraction technique. The intensities of the Bragg profiles are observed to increase anomalously with temperature above are then to drop sharply before reaching the structural transition temperature . The intensity variations and are sensitive to sample heating rate with at slow heating rates. Structural refinements indicate that the observed intensity variations are due to changes in the domain structure and the thermal parameters B with the latter becoming anomalously large several degrees Celsius below compared with those above and at room temperature, indicating the onset of significant pre-transition disorder for Ti ions along the polar c axis. The observed linewidths of the diffraction profiles reflect contributions from the anisotropic domain sizes and the internal strains and an added contribution from the coexistence of tetragonal and cubic phases below . The results suggest that the fluctuations in the Ti positions existing well below could be responsible for the broadening of dielectric response observed for BCT.

Growth and characterisation of KTa0.3Nb0.7O3 single crystals

Abstract Single crystals of KTN have been grown by the slow cooling technique for a niobium composition x of 0.7. The growth mechanism is discussed with different habits of the as-grown crystals. Compositional analysis and pyroelectric studies were carried out on the grown crystals.

The tetragonal leftrightarrow phase transition in mixed perovskite Ba1 - xCaxTiO3 single crystals: EPR evidence of impurity-induced dynamic effects

By using EPR of probe ions in (x = 0 and 0.05), clear evidence has been obtained for the existence of dynamic fluctuation between cubic and tetragonal phases in the vicinity of the phase transition temperature. This was manifested as a total absence of the EPR of in the temperature range for x = 0.05, clearly showing that there is a time-dependent interaction serving as an additional and more effective pathway of spin relaxation. The time scale of the fluctuation is estimated to be .

Growth of large single crystals of Ba1−xCaxTiO3 and their characterisation

Abstract Large optical quality Ba1−xCaxTiO3 single crystals have been grown using a flux technique with very slow cooling rates. Growth conditions were optimized with higher concentrations of Ca (above 16 mol.%). The formation of ‘cake’ or ‘excess’ twinned particles at the bottom of the crucible was completely absent for higher calcium content. A layer growth mechanism was observed on twinned and rectangular crystals. Lattice parameters decreased with increasing calcium content, and the room temperature dielectric constant was found to decrease compared to that of pure BaTiO3.

Raman study of phase transition in ferroelectric Ba0.95Ca0.05TiO3

Raman scattering investigation of phase transition in the ferroelectric Ba0.95Ca0.05TiO3 is reported. The results suggest onset of significant dynamic disorder at 105°C. This corroborates findings of recent structural study regarding large positional disorder associated with Ti and O1 atoms well below the tetragonal to cubic transition temperature (∼150°C).

Growth aspects of bismuth titanate single crystals top seeded solution growth technique

Growth aspects of Bi{sub 12}TiO{sub 20} crystals from a Bi{sub 2}O{sub 3} rich melt using low axial gradient furnace systems have been discussed. Hopper structure was observed on the melt solution surface after a soaking period which was used for right seeding temperature determination and homogenization of the melt solution. Growth rates of less than 1mm/hr. and 30 rpm result in better quality single crystals while pulling from a solution containing 10 mole % of TiO{sub 2}. The mixture HNO{sub 3} + H{sub 2}O + AcOH is the best etchant for Titanosellinite crystal.

Growth and characterisation of potassium tantalate niobate single crystals

Abstract Step cooling technique has been used to grow striations free KTa1–xNbxO3 single crystals. Variation of surface morphology and size of the crystals were discussed with respect to growth conditions. The composition of the grown crystal was determined by ESCA studies. Transition temperature and etch pit density measurements were carried out on the grown crystals.

Growth of Ba1–xCaxTiO3 single crystals and their characterisations

Abstract Different growth habits of Ba1–xCax TiO3 single crystals were observed for over wide range of growth conditions. A new peculiar morphology of Ba0.8Ca0.2TiO3 single crystal was found for fast growth rate (50°C/hr). Dielectric studies show diffused phase transition around 150°C and the dielectric constants found to be decreased compared to pure BaTiO3 single crystals.

Single-crystal neutron diffraction study of the structural phase transition in Ba0.95Ca0.05TiO3

There were two typographic errors in table 2, page 2908, of this article: the value of B11 for Ba/Ca(0,0,0) at 150 °C should read 0.62(16) and for Ti(0.5, 0.5, z) at 150 °C should read 0.48(20).