Crystallographic and Raman spectroscopic studies of microwave dielectric ceramics Ba(Ca1/3Nb2/3)O3

The crystal structure of the microwave dielectric ceramics Ba(Ca1/3Nb2/3)O3 synthesized by the molten salt method has been refined, from X-ray diffraction, in a trigonal order-disorder lattice with the P3¯m1(D3d3) space group. The lattice distortion and cation ordering are attributed to the large Ca2+ ions at B′-site, which induces a large deviation of bond valence sums of the B-site ions. The ordering degree determined by the variations of the occupancies of Ca and Nb ions is 0.44. High-resolution transmission electron microscopy (HRTEM) and Raman spectrum show the evidence in support of the 1:2 B-site order-disorder model. The complete Raman mode assignment for Ba(Ca1/3Nb2/3)O3 with order-disorder structure is also presented.