B-site order and infrared reflectivity in A(B′B″)O3 complex perovskite ceramics

Abstract

Complex perovskite A(B’B‘)O₃ ceramics with various degrees of B‐site order have been structurally and spectroscopically characterized by means of x‐ray diffraction, transmission electron microscopy, and infrared reflectivity. In Ba(Fe_1/2Nb_1/2)O₃ and Pb(Fe_1/2Nb_1/2)O₃, no order could be detected whereas Pb(In_1/2Nb_1/2)O₃, Pb(Mg_1/3Nb_2/3)O₃, and Pb(Sc_1/2Ta_1/2)O₃ (unannealed) all exhibited weak reflections associated with small ordered regions Pb(Sc_1/2Ta_1/2)O₃ was also prepared by appropriate heat treatment in the fully ordered form and exhibited strong maxima arising from the ordered superlattice in both electron and x‐ray diffraction. The infrared reflectivity (30–4000 cm⁻¹) revealed correlation between the degree of ordering and appearance of the extra mode in the 260–320 cm⁻¹ range assigned to B’–B‘ vibrations. Despite an apparently low volume fraction of ‘‘ordered material’’ in ‘‘partially ordered’’ samples of Pb(Sc_1/2Ta_1/2)O₃, the extra mode was observable. It is suggested that infrared spectroscopy is sensitive to short‐range ordering down to the nm range which is proposed to exist in between the small regions of order.