Diffuse phase transition in La and Ga doped barium titanate

Phase transitions in BaTiO3 and Ba1-xLaxTi1-xGaxO3 (Y = 0.008, 0.012, 0.016 and 0.02) have been studied by high temperature X-ray diffraction (HTXRD) and Raman spectroscopy. All the compositions in these systems exhibit a single phase. The HTXRD and Raman spectra have been recorded between room temperature and 250 degrees C. The XRD data has been analyzed using the FULLPROF Rietveld refinement package. In compositions with higher diffuseness, the tetragonal phase exists well above the transition temperature (T-max) observed in the dielectric constant vs temperature plot. Unlike pure BaTiO3 where Tmax is accompanied by a crystallographic transition, Bat(1-x)La(x)Ti(1-x)Ga(x)O(3) systems do not exhibit any crystallographic transitions at Tmax. The difference between the T-max and crystallographic transition temperature is proportional to the extent of diffuseness of the transition. (C) 2008 Elsevier Ltd. All rights reserved.