Synthesis and characterization of A-site deficient rare-earth doped BaZrxTi1-xO3 perovskite-type compounds

A-site deficient rare-earth doped BaZrxTi1-xO3 (BZT) ceramics were prepared from a soft-chemistry route and by solid-state reaction (SSR). Perovskite-like single-phase diagrams for the BaTiO3-La2/3TiO3-BaZrO3 system were constructed for each method of synthesis. Infrared spectroscopy on (Ba1-yLa2y/3)ZrxTi1-xO3 solid solution revealed a dramatic stress on the M-O (M = Ti, Zr) bonds due to the combined effect of A-site vacancies and the lower ionic radius of La3+ than that of Ba2+. A relationship between the M-O stretching vibration (v) and the tolerance factor (t) was determined. (Ba(1-y)Ln(2y/3))Zr0.09Ti0.91O3 (Ln = La, Pr, Nd) samples synthesized by SSR were selected for detailed studies. X-ray diffraction data were refined by the Rietveld method. Scanning electron microscopy on sintered compacts detected abnormal crystal growth and grain sizes in the range of about 1 pm up to 10 pm when the dopant concentration is 6.7 at. %. Impedance measurements exhibited that ferroelectric to paraelectric phase-transition temperature shifted to lower values as increasing rare-earth content. (Ba(1-y)Ln(2y/3))Zr0.09Ti0.91O3 system showed a diffuse phase transition with a relaxor-like ferroelectric behaviour. Furthermore, the dielectric constant was enhanced with respect to non-doped BZT system. (C) 2009 Elsevier Masson SAS. All rights reserved.