Optical and electronic properties in ferroelectric barium titanate-based compounds

TL;DR

This study investigates the optical and electronic properties of ferroelectric BaTiO3-based compounds with various substitutions, revealing non-linear bandgap behaviors and the effectiveness of diffuse reflectance spectroscopy for property evaluation.

Contribution

It provides new insights into the compositional dependence of bandgap energies and electronic structure in BaTiO3-based solid solutions, highlighting structural sensitivity effects.

Findings

Bandgap values show non-linear dependence on composition.

Diffuse reflectance spectroscopy reliably measures electronic properties.

Structural sensitivity influences electronic band transitions.

Abstract

The bandgap energy values for the ferroelectric BaTiO3-based solid solutions with isovalent substitution Ba1-x SrxTiO3, BaZrxTi1-xO3 and BaSnxTi1-xO3 were determined using diffuse reflectance spectra. While the corresponding unit cell volume follows Vegard's law in accordance with the different ionic radii of the ionic substitutions, the bandgap values depict non-linear compositional dependences for all the solid solutions. The effect is considerably large for BaZrxTi1-xO3 and BaSnxTi1-xO3 solutions, depicting a bandgap linear compositional dependence up to x=0.6, for x>0.6 BaZrxTi1-xO3 compounds present much larger bandgap values than BaSnxTi1-xO3 counterparts. Electronic properties have been investigated through X-ray photoelectron spectroscopy in BaSnxTi1-xO3 compounds, indicating that the Sn 3d and Ti 2p core levels shift against the Ba 3d ones within the whole compositional range with the same energy trend as that observed for the optical bandgap. Since for Ba1-x SrxTiO3 compounds no major bandgap variation is observed, we conclude that the bandgap compositional dependences observed for BaSnxTi1-xO3 compounds and BaZrxTi1-xO3 ones are originated from the structural sensitivity of the O, Ti and Sn or Zr electronic bands involved in the bandgap transition of these compounds. With this work, we underline the reliability of the bandgap determined from diffuse reflectance spectrometry experiments, as a means to non-invasively evaluate the electronic properties of powder materials.