Effect of non-stoichiometry on the densification, phase purity, microstructure, crystal structure, and dielectric loss of Ba(Co1/3Nb2/3)O3 ceramics

The structural, vibrational, densification, and microwave properties of Ba(Co1/3Nb2/3)O3 ceramics with small compositional variations along several tie lines in the ternary BaOCoONb2O5 diagram were studied. The results showed that very small deviation from stoichiometric Ba(Co1/3Nb2/3)O3 composition has profound effect on Q × f, degree of ordering, densification, and phase assemblage. The 0.94 Ba(Co1/3Nb2/3)O3-0.06 Ba5Nb4O15 ceramic has the highest Q × f value (71 THz) - a value two times larger than that of stoichiometric Ba(Co1/3Nb2/3)O3 (36 THz). Transformation from the (partial) disordered distribution of Co and Nb cations to 1:2 ordered arrangement in the octahedral sites was found to increase the Q factor of the high density and single phase ceramics. It was also observed that formation of very small amount of Ba9CoNb14O45 second phase degraded Q × f value severely for the dense and highly ordered Nb-rich and Ba-deficient ceramics.