X-ray diffraction data for the new ferroelectric tetragonal tungsten bronze phases, Ba2RETi2M3O15:M=Nb and RE=La, Pr, Nd, Sm, Gd, Dy, (Bi);M=Ta and RE=La, Nd

Abstract

X-ray powder diffraction data are presented for nine new phases with the tetragonal tungsten bronze structure. By comparison with the structure of the M=Nb,RE=La analogue, these contain Ba in the large pentagonal sites with coordination number 15, a range of large rare-earth cations and Bi in the twelve coordinate sites, and the smaller cations, Ti and either Nb or Ta, in the octahedral framework sites. The a lattice parameter data of the tetragonal unit cell show an approximately linear variation with trivalent ion radius, apart from Dy, whose value appears to be anomalous; data for c show little variation with trivalent ion radius.