Crystal structure and mechanical properties of SrSi7N10

A new highly condensed nitridosilicate phase with composition SrSi7N10 has been found in the system Sr3N2Si3N4. It has been structurally characterized by using electron diffraction and single crystal X-ray diffraction. SrSi7N10 is one of a very few nitridosilicates exhibiting both edge-sharing and corner-sharing SiN4 tetrahedrons. SrSi7N10 was obtained via three methods: (i) and (ii) by reaction of Sr metal with Si3N4 powder in a graphite furnace; (iii) by reaction of Sr metal with Si(NH2) powder. The crystal structure was determined with direct methods and refined with unit cell parameters a=6.868(5)Å, b=6.694(5)Å, c=9.614(5)Å, β=105.979(5)°, in the monoclinic space group Pc (No. 7), Z=2, and R-values R=0.041, Rw=0.039. Hardness experiments on single crystals of this compound were performed using the nano-indentation technique, yielding a hardness value of 16.1(5) GPa which is comparable to α-sialons and α-Al2O3.