DFT-assisting discovery and characterization of a hexagonal MAB-phase V3PB4

Abstract

A 314-type MAB phase V3PB4 with hexagonal crystal structure is synthesized by self-propagating high temperature combustion synthesis (SHS), with the help of the full first-principles predictions for the phase stability and adiabatic combustion temperature of SHS. Using XRD and TEM, V3PB4 crystallizes in the space group of P6¯m2, with the lattice parameters a = 3.030 Å and c = 9.148 Å, of much interest, well with the predicted one. Furthermore, the electronic structure, chemical bonding, and elastic properties of hex-V3PB4 are predicted by first-principles. No bandgap around Fermi energy indicates its electronic conductor. And the strong covalent bonding is present between the B and V atoms with, significantly, much weaker V-P bond. With the help of the theoretical model of bond stiffness, the significantly high ratio of bond stiffness of weakest bonds to the strongest ones (0.873) of hex-V3PB4 indicates its poor damage tolerance and fracture toughness. The high bond stiffness results in its high moduli in comparison with other MAB phases. As the number of inserted P atoms increases, the engineering elastic modulus decrease, without the price of an increase in density.

Keywords

• MAB phase
• Borides
• Hexagonal
• First principles
• Combustion synthesis