Kumaravinothan Sarma

Synthesis and characterisation of Ga-doped hexagonal BaTiO3

Abstract The hexagonal polymorph of BaTiO3 (P63/mmc) has been stablished at room temperature by partial replacement of Ti by Ga, where BaTi1-yGayO3-y/2 and 0.06≤y≤0.125 for samples prepared at 1300°C. The unit cell expands with increasing y and Rietveld Refinement of Neutron diffraction data shows that oxygen vacancies occur only in the hexagonal close packed layers between the face-sharing Ti2O9 dimers. Exaggerated grain growth (>100 μm) occurs for ceramics processed at ≥1400°C and/or for sintering periods ≥2 hours. Electrical measurements show the materials to be electrically insulating with room temperature permittivity values of ~70–80. Dense ceramics (94–97% of the theoretical X-ray density) resonate at microwave frequencies with Q.f values of ~4000–8000 at ~5.5 GHz.

Evaluation of Residual Stress in Thin Ferroelectric Films Using Grazing Incident X-Ray Diffraction

A comparative study of three methods for thin film, in-plane residual strain evaluation is presented. Thin films of SrTiO3 and BaxSr(1 - x)TiO3 deposited using pulsed laser deposition on LaAlO3 and MgO substrates were investigated. It is shown that the most precise way to evaluate thin film, in-plane residual strain is by using Grazing Incidence X-ray diffraction.

Sintering Behaviour of BaxSr1-xTiO3

This paper deals with the sintering behaviour of Barium Strontium Titanate (BST). Two methods were examined; method 1: BaTiO3 + SrTiO3 source powders; method 2: BaCO3 + SrCO3 + TiO2 source powders. Commercially available 50 nm BST (x = 0.60) powder was used to investigate the effect of particle size on activation energy (Ea). Discs were sintered in a Netzsch 402C Dilatometer and Ea for the powders were obtained by applying the Arrhenius expression. The results indicate powders made from both methods display a varying trend in Ea over a range of x. The commercial powder yielded a higher Ea compared with powder made from method 1.

Single- and Multi-target Pulsed Laser Deposition of Thin BSTO films: Preparation, Microstructure and Electrical Properties

A comparative study of microstructure and electrical properties of Ba x Sr 1-x TiO 3 films made by single- and multi-target pulsed laser deposition was carried out. The films were epitaxially grown on both LaAlO 3 and MgO substrates. The structural properties of all samples were investigated using X-ray diffraction and Raman spectroscopy. The elemental composition of the samples was investigated using energy dispersive X-ray analysis. For electrical properties examination, a simple capacitor structure was patterned on the film surface. Thin films made using both methods exhibit similar structural and electrical properties; however the samples made by a multi-target method underwent phase transition in a broader temperature region. The results prove the possibility of using the multi-target pulse laser deposition as a more flexible method for engineering thin film stoichometry.