Shock wave formation of defective rocksalt aluminium oxynitride rs-Al(O, N) from (Si-)Al-O-N polytypoids

Shock wave treatment of different Si-Al-O-N and Al-O-N polytypoids (27R, 21R, 12H) were performed in a pressure range of 12-25 GPa. Starting materials and shock-recovered samples were investigated using elementary analysis, synchrotron and lab-PXRD as well as 1D/2D 27Al and 29Si MAS NMR spectroscopy. Under all conditions the formation of a new phase with rocksalt structure and a lattice constant a of 4.0345 +/- 0.0016 & Aring; and 4.0300 +/- 0.0002 & Aring; for AlON and Sialon polytypoids, respectively, was observed. In 27Al MAS NMR spectra the sixfold coordination of aluminium in the high pressure phase is shown (delta iso = _ 0.5 ppm and 0.0 ppm), whereas 29Si MAS NMR spectra show no indication for sixfold coordinated silicon at all. Conclusions are given that the high-pressure phase is an oxynitride with a defective rocksalt structure with aluminium vacancies.