A new hexagonal 16L perovskite-related structure: Ba4Ca1-xMn3+xO12-delta

A new manganese oxide, Ba4Ca1-xMn3+xO12-delta, closely related to the hexag onal perovskite family has been synthesized It crystallizes in the P (6) ov er bar m2 space group with a = 5.8003(3) Angstrom and c = 38.958(1) Angstro m. This structure derives from the rare hexagonal 16L polytype and exhibits ordered oxygen deficient vacancies, so that it can be described as the sta cking along (c) over right arrow of cubic (c) and hexagonal (h) [BaO3] laye rs, with oxygen deficient cubic (c') [BaO2] layers, according to the sequen ce (hhhccc'cc)(2). This framework forms octahedral layers occuped by mangan ese and calcium and tetrahedral layers occupied by manganese. These structu ral results, together with the chemical composition, confer to manganese an unusual mixed valency.