Structure refinement, dielectric, pyroelectric and Raman characterizations of Ba1-xLax(1-y)/2Euxy/2Nax/2TiO3 solid solution

The perovskite-type oxides Ba1-xLax(1-y)/2Euxy/2Nax/2TiO3 (0 <= x <= 0.5 and xy = 0.04) were synthesized and characterized by X-ray diffraction as well as dielectric measurements and Raman spectroscopy. The crystal structure of these ceramics has been determined by the Rietveld refinement powder X-ray diffraction data at room temperature. These compounds crystallize at room temperature in tetragonal space group P4mm for 0 <= x <= 0.1 and in the cubic group Pm (3) over barm for 0.2 <= x <= 0.5. The phase transition temperature T-C (or T-m) decreases as x content increases. The degree of diffuseness of the phase transition is more pronounced for higher x content, implying the existence of a composition-induced diffuse phase transition of the ceramics with x >= 0.1. The evolution of the Raman spectra was studied as a function of various compositions at room temperature. The polarization state was checked by pyroelectric measurements. (c) 2006 Elsevier Inc. All rights reserved.