Strain engineering of functional properties: a first-principles study on pressure as a gateway for phase transition in LiTaO 3

Abstract Perovskite oxides, recognized for their excellent ambient stability, tunable synthesis, and wide bandgap characteristics, show promising applications in electronic and optoelectronic devices as semiconductor channels and transparent conductive electrodes. This work employs first-principles density functional theory (DFT) to systematically investigate the influence of hydrostatic pressure (0–60 GPa) on the structural, electronic, mechanical, and optical properties of perovskite-type LiTaO 3 . Upon increasing the pressure to 35 GPa, discontinuous variations in lattice parameters and volume, combined with a near-zero formation enthalpy (ΔH ≈ 0), clearly indicate a structural phase transition from the R3c to the Pnma phase. The absence of imaginary phonon modes and the fulfillment of mechanical stability criteria confirm the thermodynamic and mechanical stability of both phases. Analysis of elastic properties reveals that the high-pressure Pnma phase exhibits more pronounced anisotropy. Electronic structure calculations show that the R3c phase at 0 GPa has a direct bandgap of 3.205 eV, which decreases only slightly under pressure, while at the transition pressure of 35 GPa, the Pnma phase adopts an indirect bandgap of 1.26 eV. This reduced bandgap enhances light absorption in the visible to near-infrared range, suggesting potential applications in solar cell absorber layers and near-infrared LEDs. The phase transition also induces characteristic changes in the optical spectrum: the double-peak feature near 7.5 eV merges into a single peak, and all major spectral features exhibit systematic blue shifts and enhanced intensities. These optimizations highlight the potential of LiTaO 3 for vacuum ultraviolet applications, such as spacecraft monitoring and high-resolution lithography. The evolution of elastic properties with pressure is also distinctive: in the R3c phase (0–34 GPa), the bulk modulus varies non-monotonically, while shear and Young’s moduli decrease, indicating shear softening. At 35 GPa, elastic instability emerges, accompanied by anomalous negative values in shear and Young’s moduli. Beyond this point, the Pnma phase shows markedly increased moduli, indicating improved rigidity and ductility. Elastic anisotropy analysis further reveals enhanced spatial heterogeneity under pressure. This study elucidates the phase-transition-mediated mechanical evolution of LiTaO 3 , underscoring its potential in flexible electronics.