Ferroelectric properties of the tungsten bronze M2+6M4+2Nb8O30 solid solution systems

https://doi.org/10.1016/0025-5408(92)90074-AGet rights and content

Abstract

Ferroelectric compositions based on the chemical formula M2+6M4+2Nb8O30, where M2+ = Ba, Sr or Ca and M4+ = Ti, Sn or Zr, have been synthesized and their characteristics have been compared with the results of earlier work. X-ray diffraction and dielectric constant measurements show that Ba2+ analogs are tetragonal at room temperature as previously reported, with one phase transition, while the Sr2+ analogs are orthorhombic with two phase transitions. The orthorhombicity becomes pronounced on the addition of Ca2+ into the Sr2+ site and two phase transitions, paraelectric:ferroelectric and ferroelectric:ferroelastic, have been established. The solid solution between Ba6Ti2Nb8O30 and Sr6Ti2Nb8O30 was studied and found to exhibit a morphotropic phase boundary near the Sr2+ rich side. The structural and ferroelectric properties of these various bronzes are described with respect to the M2+ and M4+ cations.

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