Atomic Positions and Optical Properties of Barium Titanate

Abstract

IN view of recent discussion^1,2 of possible departures of some of the atoms of tetragonal barium titanate from the centrosymmetrical configuration of the unit cell (Ba⁺² at 0, 0, 0; Ti⁺⁴ at ½, ½, ½; O^-2 at ½, ½, 0 ; ½, 0, ½ ; and 0, ½, ½), the following may be of interest. Oscillation photographs of an untwinned crystal of nearly square cross-section (12 : 13) have been obtained, and reflexions of the type h,0,0, 0,0,l, examined. No intensity differences between these pairs of reflexions have been observed by eye, and from this it is concluded (using F values obtained from the International Tables) that there is no simple shift of the Ti⁴⁺ ion parallel to the c-axis by more than 0·05 A. or of the O^2- ion at ½, ½, 0 by more than 0·13 A. from the above positions.