Disordered crystal structure of 16<i>H</i>-SiAlON, Si_3&minus;<i>_x</i>Al₅₊<i>_x</i>O<i>_x</i>N_9&minus;<i>_x</i> (<i>x</i>~2.6)

Abstract

We prepared the 16H-SiAlON crystal with the general formula of Si3−xAl5+xOxN9−x (Z = 2), and characterized it by X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The x-value was determined to be 2.61(2) from the [Si:Al] molar ratios of [0.049(2):0.951(2)]. The space group was found to be P63/mmc (centrosymmetric) for the Si0.39(2)Al7.61(2)O2.61(2)N6.39(2) compound. The hexagonal unit-cell dimensions were a = 0.305831(7) nm, c = 4.29942(12) nm, and V = 0.348260(15) nm3. These values were in good accordance with the high correlation between the unit-cell dimensions and concentrations of octahedral layer in the unit cell, which was determined for AlN, 20H-AlON, 21R-AlON, and 27R-AlON in a previous study. The initial structural model was derived by the charge flipping method, and it was further refined by the multi-phase Rietveld method. The final structural model showed the positional disordering of two of the five types of (Si,Al) sites. The disordered crystal structure was successfully described as a statistical average of four types of domains with ordered atom configurations.