Electrical Properties and Phase Transitions in -BaB2O4 at High Pressure

The capacitance, resistance-pressure relationships for the low temperature phase of barium metaborate (-BaB2O4) have been studied at room temperature at pressure up to 16 GPa in a diamond anvil cell using capacitance and resistance measurements. Experimental results indicate that anomalous changes in capacitance with pressure occurring near 2.1, 4.6, 6.4, 8, 9.5 and 10.7 GPa. This shows the changes of structure or state in the interior of -BaB2O4 at these pressures i.e., that -BaB2O4 may undergoes phase transition. In the present work, it is known from X-ray diffraction analysis on the -BaB2O4 sample after releasing pressure from 12 GPa that the sample has become amorphous. This shows that the -BaB2O4 sample has already become amorphous state at higher pressure, and kept it after releasing. The amorphous transition pressure is about 11～12 GPa.