High Pressure Polymorphic Transitions Studied by Audio- and Radio-Frequency Techniques

Abstract

Volume and resistivity changes associated with polymorphic transitions in solids under pressure have been studied by an ac inductive method. A small coil is wound over a core of the sample, and the electrical impedance of the coil determined as a function of pressure to 65 kbar. The coil method was demonstrated in three electrically different operating regions: large skin depth, small skin depth, and an intermediate case. With large skin depth, the inductance of the coil reflects the volume of the sample core. With small skin depth, the reactance and resistance of the coil represent a mixture of volume and resistivity information, but the data may be easily analyzed to yield resistivity alone. In the intermediate case, volume and resistivity are separately displayed by the inductance and resistance, respectively. The coil method offers the advantage that volumetric transitions may be studied remotely, with no moving mechanical indicators. The sensitivity to volume change was demonstrated to be at least 0.1%.