EFFECT OF PRESSURE ON THE ATOMIC VOLUME OF GA AND TL UP TO 68 GPA

The elemental metals Ga and Tl are studied under pressure in a diamond anvil cell by energy dispersive x-ray diffraction. While Tl remains i n the high-pressure cF4 structure up to the highest pressures achieved , several phase transitions are observed in Ga. Different equation-of- state (EOS) forms are fitted to the experimental data. A detailed anal ysis of the data shows that a simple first-order EOS form can describe the isothermal pressure-volume behavior of all the phases for Ga as w ell as for Tl. Furthermore, a comparison of the structural behavior un der pressure is made for all the group-IIIA elements of the Periodic T able.