THE MELTING TEMPERATURE AND COMPRESSIBILITY OF ALPHA SILICON NITRIDE UP TO 35 GPa Y Cerenius, Institute of Earth Sciences, Uppsala University, Sweden

The melting temperature of Silicon Nitride as a function of pressure was investigated by laser-heated diamond-anvil-cell (DAC) experiments. The system consists of a stabilized cw 33W Nd:YAG laser that heats a Rhenium foil situated in the middle of the sample. The thermal radiation from the sample was collected by an imaging spectrograph together with an area CCD-detector. The spectra were fitted by a Planck's function in the range between 600 and 900 nm to obtain the temperature. The correlation between the laser-power and the temperature, that is change in the slope of the sample temperature versus laser power, together with direct observation of the heated spot for convecting movements gives the melting criterion. Pressure was determined by the Ruby fluorescence method.

The melting temperature was found to vary from 2200+/-100 K to 3600+/-200 K in the pressure range between 3.5 and 35 GPa.

The bulk modulus was determined with in-situ energy dispersive X-ray diffraction in the DAC using synchrotron radiation as the X-ray source. Pressure was determined by using Sodium Chloride as an internal standard.

The cell parameter data of the Silicon Nitride was fitted to Birch-Murnaghan equation of state keeping the pressure derivative Bó fixed at certain values in the interval between 2 and 8.The best fit was obtained for Bó = 7 resulting in a bulk modulus (Bo) of 350+/-25 GPa.