Order-disorder transition and its effect on microwave quality factor Q in Ba(Zn1/3Nb2/3)O3 system

Influences of composition deviation from stoichiometry and heat treatment on crystal phases and Q factor in Ba(Zn_1/3Nb_2/3)O₃(BZN) were studied. The structural order and the crystal phases strongly depended on the slight composition deviation from stoichiometric BZN. The maximum Q factor was obtained at the vicinity of the stoichiometric BZN. In the other regions, non-stoichiometric disordered BZN or ordered BZN with secondary phase were formed, and their Q factors were found to be low. For the stoichiometric BZN, the order-disorder phase transition occurred between 1300 and 1400^°C. The crystal-structural ordering of the stoichiometric BZN was improved by post-annealing at below its transition temperature, conserving the density and the grain size. However, no significant Q factor improvement was found. The Q factor of the stoichiometric BZN strongly depends on the density and grain size not on the crystal-structural order. These results suggest that the ceramic microstructure such as the pore and grain boundary, the secondary phase and lattice defect caused by non-stoichiometry affect the variation of the Q factor in BZN system than the crystal-structural ordering.