Structure and relaxor ferroelectric behavior of novel tungsten bronze type ceramic, Sr5BiTi3Nb7O30

TL;DR

This study reports a new lead-free tungsten bronze ceramic, Sr5BiTi3Nb7O30, exhibiting relaxor ferroelectric behavior with unique dielectric properties and nanoscale polar regions, advancing the development of environmentally friendly ferroelectrics.

Contribution

It introduces a novel tungsten bronze ceramic with relaxor properties and provides a detailed structural and dielectric analysis, highlighting the role of polar nanoregions in its behavior.

Findings

Sr5BiTi3Nb7O30 is a relaxor ferroelectric with Tm near 260 K.

The ceramic shows stronger frequency dispersion and lower phase-transition temperature than similar compounds.

Polar nanoregions are key to the relaxor behavior and dielectric response.

Abstract

A novel lead-free tungsten bronze type ceramic Sr5BiTi3Nb7O30, was prepared by a conventional solid-state reaction route. The room-temperature crystal structure shows an average structure with centro-symmetric space group P4/mbm identified by synchrotron XRD. Temperature dependence of dielectric permittivity indicates that Sr5BiTi3Nb7O30 is a ferroelectric relaxor with Tm near 260 K. The ceramic displays stronger frequency dispersion and lower phase-transition temperature compared with Sr6Ti2Nb8O30. A macroscopic and phenomenological statistical model was employed to describe the temperature dependence of their dielectric responses. The calculated size of polar nanoregions (PNRs) of Sr5BiTi3Nb7O30 compared with Sr6Ti2Nb8O30 implies that the stronger diffusion phase transition for the former is related to the disorder emerged in both A and B sites. The smaller PNRs can be activated at lower temperature but have smaller electrical dipole moment. This is the origin of relaxor behavior of Sr5BiTi3Nb7O30 with lower Tm and dielectric permittivity. The PNRs is related to a local structure with a polar space group P4bm, which contributes to the dielectric frequency dispersion of relaxor behavior. This work opens up a promising feasible route to the development of relaxor ferroelectrics in tungsten bronze type oxides.