Optical and Electrical Properties of SiO₂ under Uniaxial, Biaxial, and Isotropic Pressure: a First Principles Study

Understanding the behavior of SiO₂ under different external conditions, particularly pressure, is essential for advancing its applications. While existing literature primarily focuses on the impact of isotropic stress on SiO₂, there remains a gap in exploring the effects of uniaxial and biaxial stresses on its properties. This study aims to address this gap by investigating the novel effects of uniaxial, biaxial, and isotropic pressures on the opto-electrical properties of SiO₂ using first principles calculations. Our results reveal distinct structural adaptations of SiO₂ under different pressure conditions, demonstrating its anisotropic behavior. For example, under isotropic pressure in the interval [0.0, 12.5] GPa, the lattice parameters 5.039 < a < 4.615 Å, and 5.529 < c < 5.239 Å, and the unit cell volume ranged from 121.57 to 96.65 Å³ show reductions in values, indicating structural compression in accordance with the experimentally found values. Additionally, we investigated the electrical properties, including the complex dielectric function and conductivity. At an isotropic pressure of 0 GPa, the real refractive index of SiO₂ is approximately n = 2.04083, which increases to n = 2.20836 at 12.5 GPa, while applying uniaxial or biaxial pressure resulted in direction-dependent-refractive index highlighting the crystal's anisotropic to external pressure. Also, our study revealed that the maximum values of conductivity increased while wavelength shift decreased as a function of the applied stress on the crystal. These findings provide valuable insights into the behavior of SiO₂ single crystal under directional stresses, facilitating the design of pressure-sensitive optoelectronic devices.