Transformation of the B–O Units from Corner-Sharing to Edge-Sharing Linkages in BaMBO4 (M = Ga, Al)

Two barium-containing borates BaMBO4 (M = Al, Ga) were synthesized via the solid-state method under atmospheric pressure. The 3D configurations of BaGaBO4 and BaAlBO4 are comprised of ∞2[Ba4O16]24–/∞2[Ga4O10]8–/[B2O5]4– and ∞3[Ba4O16]24–/∞2[Al4O10]8–/[B4O10]8–, respectively, of which the [B4O10]8– units possess unusual edge-sharing [BO4]5– tetrahedra. From BaGaBO4 to BaAlBO4, the B–O units are transformed from corner-sharing to edge-sharing linkages, which arises from the directional shrinkage caused by the Ba–O and M–O skeletons. The phonon spectra of these two compounds do not show imaginary frequency at any wave vectors, indicating that both of them are kinetically stable.