X-ray diffraction study of Ba_(0.985)Na_(0.015)Ti_(0.985)Nb_(0.015)O_3, Ba_(0.6)Na_(0.4)Ti_(0.6)Nb_(0.04)O_3 and Ba_(0.3)Na_(0.7)Ti_(0.3)Nb_(0.7)O_3 compositions

摘要

The Ba_(0.985)Na_(0.015)Ti_(0.985)Nb_(0.015)O_3, Ba_(0.6)Na_(0.4)Ti_(0.6)Nb_(0.04)O_3and Bao.3Nao.7Tio.3Nbo.7O3 compositions of the (1 -X) BaTiO_3-xNaNbO_3 (BTNNx) system have been studied by X-ray diffraction and by measurements of dielectric properties. The specimens with composition BTNN (x = 0.015, 0.40 and 0.70) have been refined by the JANA program from X-ray powder diffraction data. Ceramic samples with composition (1 - x) BaTiO_3+xNaNbO_3 (where x=0.015, 0.40 and 0.70) were prepared by calcinations from appropriate mixture of BaCO_3, TiO_2, Na_2CO_3 and Nb_2O_5. The calcined powder was sintered at temperature range 1200-1400 deg C. As the composition x increased from 0.015 (and 0.70), the ferroelectric ceramics (x=0.015, FE) with tetragonal phase changed to the ferroelectric relaxors (RFE, x=0.40). RFE ceramics showed a peculiar diffuse phase transition and dielectric relaxation at the low temperature (down to 180K) due to a frustration between RFE and FE state. These ceramics present the classical ferroelectric character when 0 < =x <= 0.075 and 0.55