Synthesis and phases relationships of Si6-zAlzOzN8-z in a wide range of z

Abstract

Formation of Si6-zAlzOzN8-z from Si3N4/Al2O3/AlN mixtures was studied in a wide range of z value. Mixtures were annealed under 1 bar nitrogen flow at 1550, 1650 and 1750 °C for 1.5 and 3 h. The annealed samples were characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that in general formation of β-SiAlON phases with higher z value requires lower temperature but longer annealing time. XRD analysis revealed a high yield of β-SiAlONs (≥75 wt%) in the whole range of z value (1, 2, 3 and 4) at 1550–1650 °C (from 77% (z = 4) up to 93% (z = 3)). For z = 1 and 2 formation of β-SiAlON with z = 2 and 3 respectively was observed at 1550 °C with the yields up to ∼59 and ∼74%. At 1750 °C decomposition and sublimation of Si3N4 leads to formation of silicon poor phases derived from AlN including 12H, 15R and 21R. The only exception is a formation of Si3Al7O3N9-ζ phase with quite a high yield (∼68%) in the system relating to z = 3 at 1750 °C. As a result, some conclusions about formation of SiAlON phases in a broad Si/Al ratio range were made.