High pressure X-ray diffraction study of sodium oxide (Na2O): Observations of amorphization and equation of state measurements to 15.9 GPa

We have investigated the high-pressure behavior of sodium oxide (Na2O) up to 30 GPa by synchrotron angle-dispersive powder X-ray diffraction in a diamond anvil cell at room temperature. Between 15.9 and 17.3 GPa crystalline Na2O transforms to an amorphous state, and on decompression the amorphous structure recrystallizes back between 4.9 and 10.3 GPa. The zero-pressure bulk modulus of Na2O is obtained in experimental observations for the first time. The pressure-volume data is fitted according to the third-order Birch-Murnaghan equation of state and yields four bulk modulus values by setting the V0 or B0’ either as a constant or variable. The bulk modulus values of Na2O are smaller than α-Li2O, which is in good agreement with the previous calculation results. •A reversible phase transition of Na2O to an amorphous state is observed.•The bulk modulus of Na2O is obtained in experiment.