New Fluoride Borate Solid–Solution Series Ba4–xSr3+x(BO3)4–yF2+3y

A lot of attention has been paid recently to the non-centrosymmetric fluoride borates with chemical formula BaMBO3F (M = Ca, Mg, Zn). A new BaSrBO3F phase has been synthesized by the solid-state reaction, and single crystals have been grown in the BaSrBO3F–NaF system. According to the X-ray single-crystal structure analysis, the compound crystallizes in the space group P63mc. The distinguished feature of the determined structure is the simultaneous cationic (Ba2+ ↔ Sr2+) and anionic (3F)3– ↔ (BO3)3– isomorphisms, implying the existence of the solid-solution series Ba4–xSr3+x(BO3)4–yF2+3y. The Ba4Sr3(BO3)4F2 and Ba3Sr4(BO3)4F2 end-members have been synthesized by solid-state reaction. The existence of Ba4Sr3(BO3)3F5 and Ba3Sr4(BO3)3F5 end-members has not been confirmed.