LAUSR

The ability of group III phosphates to adopt a two-dimensional van der Waals (2D VDW) structure observed for SiO2 was evaluated using density functional theory. The energies to form 2D hexagonal bilayers of corner-sharing tetrahedra did not follow a monotonic trend: the energies for AlPO4 and GaPO4 were similar to silica, while for BPO4 it was more than a factor of 2 larger and for InPO4 nearly another factor of 2 larger. The larger In atom favors octahedral coordination, accounting for the high energy of the 2D InPO4 structure. Meanwhile, boron’s small size leads to a different favored bulk structure than AlPO4 or GaPO4 which competes much more successfully with the 2D phase. The implication is a sweet spot in the cation size for forming 2D tetrahedral oxides that spans Si to Ga. The 2D BPO4 and GaPO4 structures displayed alternating rotations of the B(Ga)O4 and PO4 tetrahedra which allowed the B(Ga)–O–P bond angles to match those seen in the favored bulk compounds; no such rotations were required for 2D...