Crystal structure and mechanical properties

摘要

A new highly condensed nitridosilicate phase with composition SrSi_7N_(10) has been found in the system Sr_3N_2-Si_3N_4. It has been structurally characterized by using electron diffraction and single crystal X-ray diffraction. SrSi_7N_(10) is one of a very few nitridosilicates exhibiting both edge-sharing and comer-sharing SiN_4 tetrahedrons. SrSi_7N_(10) was obtained via three methods: (i) and (ii) by reaction of Sr metal with Si_3N_4 powder in a graphite furnace; (iii) by reaction of Sr metal with Si(NH_2) powder. The crystal structure was determined with direct methods and refined with unit cell parameters a= 6.868(5) A, b = 6.694(5) A, c = 9.614(5) A, p = 105.979(5) deg, in the monoclinic space group Pc (No. 7), Z = 2, and R-values R = 0.041, R_w = 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 alpha-sialons and alppha-Al_2O_3.