Pressure-Induced Evolution of Structure and Conduction Mechanism Transition in Ba_0.5Sr_0.5TiO₃

Barium strontium titanate (BST) is a prototypical perovskite ferroelectric with promising applications in high-performance electronic devices. In this work, the evolution of structural, ferroelectric, and dielectric properties of Ba_0.5Sr_0.5TiO₃ under pressure was systematically investigated using multiple in situ characterization techniques at high pressures, including synchrotron X-ray diffraction, Raman spectroscopy, alternating current (AC) impedance spectroscopy, and ferroelectric hysteresis loop measurements. Meanwhile, the underlying physical mechanism was elucidated via first-principles density functional theory (DFT) calculations. The results demonstrate that Ba_0.5Sr_0.5TiO₃ undergoes a continuous structural phase transition from the tetragonal phase (P4mm) to the cubic phase ($Pm\stackrel{-}{3}m$) in the pressure range of 10-18 GPa, which is concurrent with its ferroelectric-to-paraelectric phase transition. High pressure suppresses the off-center displacement of Ti⁴⁺ cations within the TiO₆ octahedra, resulting in the vanishing of spontaneous polarization and a significant reduction in relative permittivity. Concomitantly, the dielectric loss increases due to the emergence of electronic conduction in the paraelectric phase of Ba_0.5Sr_0.5TiO₃. DFT calculations confirm that the band gap narrowing accounts for the enhanced electronic conductivity. This work establishes a clear pressure-driven structure-property correlation for BST, deepens the understanding of the high-pressure response mechanism of perovskite ferroelectrics, and provides experimental and theoretical insights for designing high-pressure-tolerant ferroelectric devices.