Structure of jadeite melt at high pressures up to 4.9 GPa

The structure of jadeite (NaAlSi ₂O ₆) melts has been studied using multiple-angle energy-dispersive x-ray diffraction up to 4.9 GPa and 1923 K. The first sharp diffraction peak in the structure factor shifts toward higher momentum transfer as pressure increases, indicating the shrinkage of the intermediate network in the melt. The radial distribution function shows a monotonous decrease in average T-T length and T-O-T angle with increasing pressure, but displays no detectable change in the average bond length between tetrahedrally coordinated cations and oxygen (T-O length, where T Si ⁴, Al ³). Our observations indicate that the dominant structural changes occur in the intermediate range order at pressures up to 4.9 GPa. The changes in T-O length, T-T length, and T-O-T angle appear to correlate with the viscosity anomaly in this pressure range.