Pressure-induced phase transitions of hydrotalcite by electrical resistivity, structural and thermal studies

We report for the first time the high-pressure electrical resistivity measurements on synthetic hydrotalcite up to 6 GPa at room temperature. Pressure dependence of the electrical resistivity of synthetic hydrotalcite reveals two pressure-induced irreversible phase transitions at about 1 and 3 GPa, respectively. The first transition was accompanied by decrease of electrical resistivity 30% at about 1.5 GPa and the second phase transformation was characterized by observing a first-order decrease of electrical resistivity (about 60%) at similar to2.5-3 GPa. The high-pressure phases were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopic, and differential thermal analysis studies on the pressure-quenched samples. The spectroscopic and structural studies on the pressure-quenched samples show that hydrotalcite transforms irreversibly to manasseite phase at about 1.5 GPa and further compression leads to pressure-induced amorphization of the manasseite phase of the sample at pressures 4-4.5 GPa. The thermal (DTA/TG) studies also confirm the different high-pressure modifications of hydrotalcite. (C) 2002 Elsevier Science Inc. All rights reserved.