  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.
