Diffuse ferroelectric phase transition and long-range order of dilute KTa1-xNbxO3.

Abstract

Refractive-index and linear-birefringence measurements on $\mathrm{K}{\mathrm{Ta}}_{1\ensuremath{-}x}{\mathrm{Nb}}_{x}{\mathrm{O}}_{3}$, with $x=0.008, 0.012, \mathrm{and} 0.02$, reveal smeared phase transitions into long-range order. In accordance with previous caloric, second-harmonic---generation, dielectric, and x-ray results, the crystal optical data can be explained on the basis of a "cooperative dipole glass" model. This involves local ordering within the finite Curie region of a diffuse phase transition followed by a strain-induced collective reorientation of frozen-in microdomains.