Order-disorder behavior in Ba(Zn1/3Ta2/3)O3

Sintered (1475 degreesC/2 h) pellets of Ba(Zn1/3Ta2/3)O-3 were annealed at temperatures ranging from 1550 to 1625 degreesC/15 h and subsequently quenched into water. The degree of B-site order between the Zn and Ta cations was investigated using x-ray diffraction (XRD) and transmission electron microscopy (TEM). Samples quenched from 1575 to 1600 degreesC exhibit the, highest degree of order by XRD. Dark-field TEM images from these samples revealed 1:2, Zn:Ta, trigonal, ordered domains approximately 0.4 mum diam near grain boundaries but 100 nm in the grain interior. Samples annealed and quenched from 1625 degreesC exhibited no ordered superlattice reflections by XRD. However, diffuse scatter along [111] directions and fee rather than trigonal ordered reflections were observed in electron diffraction patterns. Disordered samples were subsequently annealed at 1500 degreesC/15 h (below the order-disorder phase transition similar to 1625 degreesC) and +/-1/3{hkl} superlattice reflections reappeared in XRD patterns demonstrating the reversibility of the phase transition. (C) 2000 American Institute of Physics. [S0021-8979(00)03220-5].