Sm2Si3O3N4 and Ln(2)Si(2.5)Al(0.5)O(3.5)N(3.5) (Ln = Ce, Pr, Nd, Sm, Gd) -A novel synthetic approach for the preparation of N-containing melilites and X-ray single-crystal structure determination

The high-temperature synthesis of nitridosilicates using an especially deve loped rf furnace was now transferred to the preparation of single-crystalli ne oxonitridosilicates and oxonitridoaluminosilicates (sialons). Sm2Si3O3N4 was obtained by the reaction of SrCO3, Si(NH)(2), and the respective lanth anoides, for Ln(2)Si(2.5)Al(0.5)O(3.5)N(3.5) (Ln = Ce, Pr, Nd, Sm, Gd) addi tionally AIN was used. The compounds were obtained as coarsely crystalline products. Their crystal structures were refined on the basis of single-crys tal X-ray diffraction data. Sm2Si3O3N4 (a = 768.89(4), c = 499.60(4) pm) an d the isotypic sialons Ce2Si2.5Al0.5O3.5N3.5 (a = 779.20(3), c=506.94(4)pm) , Pr2Si2.5Al0.5O3.5N3.5 (a=778.26(4), c= 508.56(5) pm), Nd2Si2.5Al0.5O3.5N3 .5 (a = 776.15(4), c= 506.7(3) pm), Sm2Si2.5Al0.5O3.5N3.5 (a = 772.63(13), c= 502.80(9) pm), and Gd2Si2.5Al0.5O3.5N3.5 (a = 774.15(5), c = 506.46(4) p m) are new representatives of the N-containing melilite structure type (spa ce group P (4) over bar 2(1)m (no. 113), Z = 2). For the structure analysis specific models were applied, which have been developed by Werner et al. o n the basis of powder diffraction data.