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](1/3)Nb-2/3)O-3-0.1Ba(Ga0.5Ta0.5)O-3 (BCZN-BGT) ceramic resonators (quality factor, Q = 32,000 at the rate of 3.05 GHz, relative permittivity, epsilon(r) = 35 and temperature coefficient of the resonant, tau(f) = 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 angstrom) 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 similar to 1200 degrees C. Annealing below this temperature (1100 degrees C) gave rise to discrete +/- 1/3{hkl}(p) and diffuse (1/2){hkl}(p) superlattice reflections in the same < 110 >(p) zone axis electron diffraction patterns and the presence of F-2g and A(1g) modes in Raman spectra. It is proposed that +/- 1/3{hkl}(p) reflections result from 1:2 long-range ordered domains of BCZN whereas the diffuse 1/2{hkl}(p) reflections arise from short range fee ordered BGT rich regions at the 1:2 domain boundaries. A short-range ordered fee superlattice was observed in samples quenched from above the order-disorder phase transition (> 1200 degrees C) which was accompanied by the presence of only the A(1g) mode in Raman spectra. (c) 2004 Elsevier Ltd. All rights reserved.