Pressure-Driven Evolution of the Physical Properties of Layered Y2GaB and Y2InB MAB Phases: A Comparative First-Principles Study

Abstract

MAB phases are nanolaminated ternary borides in which strong in-plane M-B bonds and weaker interlayer interactions drive their distinctive stability and functionality. Hydrostatic pressure offers a direct route to tune the in-plane and interlayer interactions that govern the stability and functionality of layered Y2GaB and Y2InB borides. Here, first-principles calculations are used to compare their structural, elastic, thermophysical, electronic, bonding, optical, and vibrational responses from 0 to 20 GPa. Elastic criteria show that Y2GaB is stable at 0, 5, and 10 GPa, whereas Y2InB is stable only at ambient pressure. Within the stable Y2GaB range, compression increases the elastic moduli, acoustic velocities, Debye temperature, and lattice thermal conductivity while reducing the elastic anisotropy. Both compounds are multiband metals and spin-orbit coupling modifies local dispersions without opening a gap. Y2GaB retains nine Fermi-surface sheets from 0 to 10 GPa, whereas Y2InB has eight at ambient pressure, with no pressure-induced topological reconstruction. Charge-density and overlap analyses indicate mixed ionic-covalent Y-B bonding within a delocalized metallic background. Optical parameters are anisotropic. Unit-cell phonon spectra contain positive frequencies at 0 and 10 GPa, although expanded-supercell calculations reveal low-frequency sensitivity. These results establish mechanically viable pressure windows and clarify substitution-driven structure-property relationships for these borides.