Hexagonal polymorphism induced structural disorder and dielectric anomalies of Ca/Mn modified BaTiO3

TL;DR

This study investigates how Ca and Mn doping induce hexagonal polymorphism, structural disorder, and dielectric anomalies in BaTiO3, revealing phase coexistence, band gap reduction, and defect-related local structural changes.

Contribution

It provides a comprehensive analysis of how Ca/Mn modification causes structural disorder, phase coexistence, and dielectric property variations in BaTiO3, combining experimental and theoretical insights.

Findings

Coexistence of tetragonal and hexagonal phases in modified BaTiO3

Band gap reduction from 3.2 eV to 2 eV due to doping

Structural disorder linked to defect-induced local lattice modifications

Abstract

This work involves the local structural investigation of the samples using Extended X-ray Absorption Spectra (EXAFS) analysis to investigate structural changes due to the Ca and Mn-modified BaTiO3. TEM investigation of the crystal structure reveals the coexistence of the tetragonal and hexagonal phases of BaTiO3. Band gap modification and Urbach tail variation in UV-DRS measurements reveal a reduction of band gap from UV to Visible range (3.2 eV to 2 eV). This band gap change is correlated with the valence band modification observed in PES measurements due to localised defects in the material, and supported by theoretical Density of States calculations. The electron localisation function calculation is used to analyse the changes in the localised electron density near the dopant atoms. It reveals the local expansion and contraction of the lattice surrounding the dopant atom. All these structural modifications lead to variations in the dielectric properties and diffusive nature of the phase transition. The defect-induced structural modifications, multiple phase coexistence, band gap variations and dielectric properties are explored and correlated.