Synthesis and characterization of A-site deficient rare-earth doped BaZr_xTi_(1-x)O_3 perovskite-type compounds

摘要

A-site deficient rare-earth doped BaZr_xTi_(1-x)O_3 (BZT) ceramics were prepared from a soft-chemistry route and by solid-state reaction (SSR). Perovskite-like single-phase diagrams for the BaTiO_3-La_(2/3)TiO_3-BaZrO_3 system were constructed for each method of synthesis. Infrared spectroscopy on (Ba_(1-y)La_(2y/3))Zr_xTi_(1-x)O_3 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 La~(3+) than that of Ba~(2+). A relationship between the M-O stretching vibration (v) and the tolerance factor (t) was determined. (Ba_(1-Y)Ln_(2y/3))Zr_(0.09)Ti_(0.91)O_3 (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 μm up to 10 μ m when the dopant concentration is 6.7 at. percent. 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))Zr_(0.09)Ti_(0.91)O_3 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.