Bandgap Engineering of BaTiO₃ - Ferroelectric and Optical Characteristics Under Strain

Lead-free perovskite oxide, BaTiO_3, has a large electro-optical coefficient, high dielectric constant, UV absorption, and above-room-temperature ferroelectricity, making it ideal for energy storage, non-volatile data retention, and precise control in optoelectronic devices. Quantum ATK based on DFT was used to compute the structural, electronic, ferroelectric, and optical characteristics of cubic and tetragonal BaTiO₃ phases. Using the hybrid GGA function, cubic and tetragonal bandgaps were calculated as 3.032 and 3.204 eV. The electrical properties and crystal structure of BaTiO₃ were greatly affected by different strain conditions. Tensile strain in cubic and tetragonal BaTiO₃ retains indirect bandgap transition. Compressive strain enhances electron mobility and conductivity by switching from semiconductor to semimetal at ~21-35% strain over threshold values. Strain engineering in cubic BaTiO₃ affects its lattice structure and ferroelectric polarisation. Tensile and compressive strains stretch the lattice, enhancing polarization, whereas biaxial and uniaxial strains govern expansions and contractions, improving ferroelectric properties. The cubic phase has no spontaneous polarization, but strain conditions cause spontaneous polarization in the tetragonal phase, highlighting the effect of phase transitions and strain on the ferroelectric property of BaTiO₃. Cubic phase BaTiO₃ exhibits high dielectric response, metalloid-like behavior, and strong UV wavelength-dependent absorption. The anisotropic nature of the tetragonal phase, with varying ε_r and ε_i peaks, enables directional control over the optical and electrical properties of BaTiO₃. The ferroelectric and optical properties of BaTiO₃ are vital for bandgap engineering, allowing the design of ferroelectric materials for electro-optic applications.