High-temperature synthesis, single-crystal X-ray and neutron powder diffraction, and materials properties of Sr(3)Ln(10)Si(18)Al(12)O(18)N(36) (Ln = Ce, Pr, Nd)-novel sialons with an ordered distribution of Si, Al, O, and N

The novel oxonitridoaluminosilicates (sialons) Sr(3)Ln(10)Si(18)Al(12)O(18) N(36) (Ln = Ce, Pr, Nd) were obtained by the reaction of the respective lan thanide metals with Si(NH)(2), SrCO3, and AlN using a radiofrequency furnac e at temperatures between 1550-1650 degrees C. The crystal structures of th e isotypic sialons were determined by single-crystal X-ray investigations ( Sr3Ce10Si18Al12O18N36: I (4) over bar 3m, Z = 2, a = 1338.2(2) pm, R1 = 0.0 333; Sr3Pr10Si18Al12O18N36: a = 1334.54(6) pm, R1 = 0.0296; Sr3Nd10Si18Al12 O18N36: a = 1332.85(6) pm, R1 = 0.0271) and in the case of Sr3Pr10Si18Al12O 18N36 with powder neutron diffraction as well. The three-dimensional sialon network is built up by SiON3, SiN4, and AlON3 tetrahedra. Besides the brid ging O and N atoms of the sialon network there are isolated O2- which are t etrahedrally coordinated by Sr and Ln. The crystallographic differentiation of Si/Al and O/N seemed to be possible by a careful evaluation of the sing le-crystal X-ray diffraction data combined with lattice energy calculations using the MAPLE concept (Madelung Part of Lattice Energy). In the case of Sr3Pr10Si18Al12O18N36 the differentiation of O and N and the proposed order ing was completely confirmed by powder neutron diffraction.