Sr10[(PO4)5.5(BO4)0.5](BO2): Growth and crystal structure of a strontium phosphate orthoborate metaborate closely related to the apatite-type crystal structure

Single crystals of the strontium phosphate orthoborate metaborate, Sr10[(PO4)5.5(BO4)0.5](BO2), were grown from the melt and investigated by X-ray diffraction (space group View the MathML sourceP3¯, No. 147; a=9.7973(8) Å, c=7.3056(8) Å, V=607.29(10) Å3, Z=1). The crystal structure is closely related to apatite and contains linear metaborate groups, [BO2]− (point group D∞h, B–O=1.284(11) Å) taking positions within the channels running along the three-fold inversion axis. Strontium sites are found to be fully occupied while [PO4]3− tetrahedra are partially replaced by [BO4]5− groups.