High temperature syntheses of novel nitrido- and oxonitrido-silicates and sialons using rf furnaces

The high-temperature reaction of pure metals with silicon diimide Si(NH)(2) in a specially developed radiofrequency furnace has been successfully applied to the synthesis of novel highly condensed nitridosilicates. With SrCO3 as an additional starting material this procedure has now been extended to the synthesis of oxonitridosilicates and oxonitridoaluminosilicates (sialons). Two novel sialons SrSiAl2O3N2 [space group P2(1)2(1)2(1) (no. 19), a = 491.89(6), b = 789.73(7), c = 1134.94(18) pm, Z = 4] and SrErSiAl3O3N4 [space group P6(3)mc (no. 186), a = 606.53(3), c = 985.90(8) pm, Z = 2] have been obtained as coarsely crystalline materials. According to single crystal X-ray diffraction both compounds adopt structure types which are unprecedented for sialons. They derive from the nitridosilicates LnSi(3)N(5) (Ln = La, Ce, Pr, Nd) and MYbSi4N7 (M = Sr, Ba, Eu),respectively, by partial substitution of Si by Al and N by O. For SrSiAl2O3N4 and SrErSiAl3O3N4 an unambiguous crystallographic differentiation between the tetrahedral centres (Al and Si) as well as the bridging atoms of the framework structures (N and O) seems reasonable.