Synthesis of low-density from high-density in the presence of melt under high pressure

In general, the high-density state is a preferred state of materials under high pressures. In this study, however, when the LiBO2–Al2O3 system quenched from melts at the cooling rate of 50–60 °C/s under high pressures, low density γ - Al2O3 was synthesized from high density α - Al2O3, with a 7.1% volume expansion of Al2O3. While those samples which are quenched at the same cooling rate under a lower pressure appeared to be glassy. The minimal pressure synthesized the low-density γ - Al2O3 or the maximal glass forming pressure was decreased with increasing content of Al2O3 below its saturation point in LiBO2 melt.