Small compressive strain tuning of α-TeO2 and β-TeO2 polymorphs: Electronic, linear, and nonlinear optical properties from first-principles calculations

This study examines the effects of 2 % compressive strain on the structural, electronic, and optical properties of α-TeO₂ and β-TeO₂ polymorphs. α-TeO₂’s bandgap increases from 3.64 eV to 3.70 eV, while β-TeO₂’s decreases from 3.632 to 3.53 eV. Lattice parameters uniformly reduce in α-TeO₂, but vary dissimilarly in β-TeO₂. PDOS analysis shows O-2p and Te-5p states dominate near the band edges. Optical behavior is anisotropic, with enhanced polarizability and refractive indices under strain. Nonlinear optical properties improve with increased strain, especially the non-linear susceptibility components, which are relevant for second-harmonic generation. Born Effective Charges show increased Te polarization and reduced oxygen polarization, impacting dielectric response.