Novel optically active lead-free relaxor ferroelectric (Ba0.6Bi0.2Li0.2)TiO3

TL;DR

This study introduces a new lead-free relaxor ferroelectric material, (Ba0.6Bi0.2Li0.2)TiO3, exhibiting unique dielectric and optical properties near room temperature, with potential environmental benefits and applications.

Contribution

The paper reports the discovery and detailed characterization of a novel lead-free relaxor ferroelectric with optically active centers and specific structural and dielectric properties.

Findings

Displays slim polarization-hysteresis loops near room temperature

Exhibits nonlinear Vogel-Fulcher dielectric dispersion

Contains mixed valence bismuth ions responsible for optical activity

Abstract

We discovered a near room temperature lead-free relaxor-ferroelectric (Ba0.6Bi0.2Li0.2)TiO3 (BBLT) having A-site compositional disordered ABO3 perovskite structure. Microstructure-property relations revealed that the chemical inhomogeneities and development of local polar nano regions (PNRs) are responsible for dielectric dispersion as a function of probe frequencies and temperatures. Rietveld analysis indicates mixed crystal structure with 80% tetragonal structure (space group P4mm) and 20% orthorhombic structure (space group Amm2) which is confirmed by the high resolution transmission electron diffraction pattern. Dielectric constant and tangent loss dispersion with and without illumination of light obey nonlinear Vogel-Fulture relation. It shows slim polarization-hysteresis (P-E) loops and excellent displacement coefficients (d33 ~ 233 pm/V) near room temperature, which gradually diminish near the maximum dielectric dispersion temperature (Tm). The underlying physics for light-sensitive dielectric dispersion was probed by X-ray photon spectroscopy (XPS) which strongly suggests that mixed valence of bismuth ions, especially Bi5+ ions, are responsible for most of the optically active centers. Ultraviolet photoemission measurements showed most of the Ti ions are in 4+ states and sit at the centers of the TiO6 octahedra, which along with asymmetric hybridization between O 2p and Bi 6s orbitals appears to be the main driving force for net polarization. This BBLT material may open a new path for environmental friendly lead-free relaxor-ferroelectric research.