Order–disorder behaviour in 0.9Ba([Zn0.60Co0.40]1/3Nb2/3)O3–0.1Ba(Ga0.5Ta0.5)O3 microwave dielectric resonators

0.9Ba([Zn0.60Co0.40]1/3Nb2/3)O3–0.1Ba(Ga0.5Ta0.5)O3 (BCZN–BGT) ceramic resonators (quality factor, Q=32,000 at the rate of 3.05 GHz, relative permittivity, εr=35 and temperature coefficient of the resonant, τf=0) have been fabricated which are suitable in terms of cost and performance for base stations supporting third generation architecture. The new compounds are perovskite structured (a=4.09 Å) but exhibit no superlattice reflections at any heat treatment temperature according to X-ray diffraction (XRD). However, annealing and quenching of samples followed by transmission electron microscopy and Raman spectroscopy revealed an order–disorder phase transition at ∼1200 °C. Annealing below this temperature (1100 °C) gave rise to discrete ±1/3{h k l}p and diffuse 1/2{h k l}p superlattice reflections in the same 〈1 1 0〉p zone axis electron diffraction patterns and the presence of F2g and A1g modes in Raman spectra. It is proposed that ±1/3{h k l}p reflections result from 1:2 long-range ordered domains of BCZN whereas the diffuse 1/2{h k l}p reflections arise from short range fcc ordered BGT rich regions at the 1:2 domain boundaries. A short-range ordered fcc superlattice was observed in samples quenched from above the order–disorder phase transition (>1200 °C) which was accompanied by the presence of only the A1g mode in Raman spectra.