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

Abstract

Sintered (1475 °C/2 h) pellets of Ba(Zn 1/3 Ta 2/3 )O 3 were annealed at temperatures ranging from 1550 to 1625 °C/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 °C 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 μm diam near grain boundaries but 100 nm in the grain interior. Samples annealed and quenched from 1625 °C exhibited no ordered superlattice reflections by XRD. However, diffuse scatter along 〈111〉 directions and fcc rather than trigonal ordered reflections were observed in electron diffraction patterns. Disordered samples were subsequently annealed at 1500 °C/15 h (below the order–disorder phase transition ∼1625 °C) and ± 1 3 {hkl} superlattice reflections reappeared in XRD patterns demonstrating the reversibility of the phase transition.