Über hexagonale Perowskite mit Kationenfehlstellen. XXXIII. Verbindungen vom Typ Ba6−xSrxB2−y3+SEy3+W3□O18

On Hexagonal Perovskites with Cationic Vacancies. XXXIII. Compounds of Type Ba_6?xSr_xB_2?y³⁺SE_y³⁺W₃□O₁₈ In the series Ba_6?xSr_xLu_2?ySE_y³⁺W₃□O₁₈ a substitution of Sr²⁺ for Ba²⁺ is possible. According to intensity calculations on powder data of BaSr₅Lu_1,6Ho_0,4W₃□O₁₈ the compounds crystallize in a rhombohedral 18 L type with the sequence (hhcccc)₃; space group R3 m. The refined, intensity related R' value is 11.5%. The differences in properties (diffuse reflectance spectra, photoluminescence) between the hexagonal modifications Ba₆B_2?y³⁺SE_y³⁺W₃□O₁₈ (B³⁺ ? Gd, Y, Lu; SE³⁺ ? Sm, Eu, Tb, Dy, Ho, Er, Tm) and the corresponding cubic HT modifications are discussed.