A careful phase analysis and TEM investigation of the incommensurately modulated, (Bi1-xMII)FeIIIO3-x/2 (M = Ca and Sr), solid solution phases

Abstract

A careful phase (Bi1-xCax)FeIIIO 3-x/2Vx/2 (V for vacancy), ∼0.20 ≤ x(Bi 1-xSrx)Fe3+O3-x/2Vx/2, 0.2 ≤ x ≤ 0.67, perovskite related solid solution fields has been carried out. Both solid solution fields are, in general, (3+1)-d incommensurately modulated with an incommensurate primary modulation wave-vector magnitude that varies systematically with composition. High Resolution (HR)TEM imaging is used to show the presence of at least 6-fold twinning on a sometimes rather fine scale, the fine scale twinning being more prevalent in the M = Sr than the M = Ca system. The (3+1)-d superspace group symmetry is suggested to be Cmmm (01γ) 0s0 or one of the non-centrosymmetric sub-groups thereof. The magnetic and electrical properties of the systems are briefly discussed and a tentative structural model proposed. © 2010 IOP Publishing Ltd.