Pressure-induced polymorphism in Al3BC3: A first-principles study

Al₃BC₃, an isostructural phase to Mg₃BN₃, experienced no pressure-induced phase transformation that occurred in the latter material (J. Solid State Chem. 154 (2000) 254-256). The discrepancy is not clear yet. Using the first-principles density functional calculations, we predict that Al₃BC₃ undergoes a hexagonal-to-tetragonal structural transformation at 24 GPa. The predicted phase equilibrium pressure is much higher than the previously reported pressure range, i.e., 2.5-5.3 GPa, conducted on phase stability of Al₃BC₃. A homogeneous orthorhombic shear strain transformation path is proposed for the phase transformation. The transformation enthalpy barrier is estimated to yield a low value, i.e., 0.129 eV/atom, which ensures that the transformation can readily take place at the predicted pressure.