COMPRESSIBILITY MEASUREMENTS OF BETA-ALUMINA AND BETA''-ALUMINA

The compressibilities of the a- and c-axes for sodium beta- and beta'' -aluminas were determined up to 10 GPa from the pressure dependence of powder X-ray diffraction measured at room temperature using synchrotr on radiation as an X-ray source. Powders of sodium beta- and beta''-al uminas which were prepared from grinding synthesized single crystals w ere used as the specimens for X-ray diffraction. The compressibilities of beta- and beta''-aluminas are 1.5 +/- 0.2 X 10(-12) and 1.7 +/- 0. 2 x 10(-12) Pa-1 for the a-axis and 2.9 +/- 0.2 X 10(-12) and 1.6 +/- 0.2 X 10(-12) Pa-1 for the c-axis, respectively. For the c-axis, the c ompressibility of beta-alumina is larger than that of beta''-alumina. This experimental fact is explained by the different stacking of oxyge n layers and the different content in sodium ion between beta- and bet a''-aluminas.