Crystal structure, dielectric, and ferroelectric characteristics of zirconate tantalate ceramics with tungsten bronze structure

In the present work, dielectric and ferroelectric characteristics of Ba6-pRpZr2+pTa8-pO30 (p = 1, 2, R = La, Nd, Sm) tungsten bronze ceramics were investigated systematically, and the effects of Zr4+ and Ta4+ occupation upon the polar order were emphasized. X-ray diffraction patterns confirmed the tetragonal tungsten bronze structure with P4/mbm space group at ambient temperature. Relaxor ferroelectric behavior was determined for all compounds, even for those who had order A1- and A2-site occupations, and this was quite different from other tungsten bronze systems. Compared with the Ti- and Nb-based analogue, these Zr- and Ta-based compounds exhibited stronger relaxor nature and obvious polar order disruption. Raman spectra and X-ray photoelectron spectra demonstrated distinct local crystal environment for these compounds with different B-site substitutions. Smaller A-site cation displacement inside the pentagonal channels, frustrating BO6 deformation, and weaker B-O-bond covalency were the main reasons for the severe disruption of ferroelectric polar order in these filled tungsten bronzes.