Neutron powder diffraction study and B-site ordering in microwave dielectric ceramics Ba(Ca_(1/3)Nb_(2/3))O_3

摘要

Microwave dielectric powder Ba(Ca_(1/3)Nb_(2/3))O_3 with high B-site cation ordering was synthesized by the molten salt method. Neutron powder diffraction (NPD) and Raman scattering spectra were introduced to investigate the variable ordering degree during the sintering process. It was revealed that the as-synthesized Ba(Ca_(1/3)Nb_(2/3))O_3 powder had a nearly completely ordered structure, and the sintered Ba(Ca_(1/3)Nb_(2/3))O_3 presented a bit higher ordering degree based on the detailed quantitative NPD Rietveld full profile fitting. The complete Raman mode assignment for the Ba(Ca_(1/3)Nb_(2/3))O_3 was presented. The phonon bands could also confirm the order-disorder structural model and increasing ordering degree with the increasing sintering temperature. Final microwave dielectric measurements on sintered samples showed the present compound to tailor other dielectric materials for microwave applications with the dielectric properties of epsilon_r = 47.11, and Qf= 1389 GHz, and tau_f was about 113ppm/ deg C.