Application of the AC Impedance Spectroscopy at High Pressures: Electrophysical Properties of Sulfur

Abstract

Keywords: sulfur, high pressures, ac impedance spectroscopy Abstract. The ac impedance spectroscopy is applied to the study of physical properties of sulfur at high pressures. The measurements were carried out in a frequency range 1 Hz - 100 kHz and in a pressure interval 20 - 50 GPa at room temperature. The results of the observations can be connected with known phase transitions in sulfur. Introduction During the studies of the electrophysical characteristics of materials it is of crucial importance to eliminate the effect of processes leading to a distortion of the electroconductivity values of the studied sample. These are phenomena occurring on the interface between the electrode and the sample, blocking of carriers of a charge on electrodes, formation and relaxation of volumetric charges and others. Determination of the contribution of these processes in the system is possible when measurements of the complex resistance of the object are carried out in a wide range of frequencies of an alternating current (impedance spectroscopy). Substances undergo structural transformations at high pressures and their electronic structures are considerably changed. Application of the ac impedance spectroscopy can give new information on the dynamic of transformations at high pressure, conditions of origin of new phases, and borders of their stability. Thus impedance spectroscopy in a wide frequency range allows to determine the contribution to the electrical characteristics of the system coming from the sample, surface, the measuring cell, and is well suited for the investigations of phase transformations. Experimental High pressure has been generated in the diamond anvil cell (DAC) with anvils of the cone-plane (Verechagin-Yakovlev) type made of synthetic carbonado-type diamonds [1,2]. These anvils are good conductors and allow to measure the electrophysical properties of the sample placed in the DAC. In our experiments we used rounded cone top anvil with radius near 1 cm. The diameter of the contact spot was about 0.2 cm. For the measurements sulfur powders of orthorhombic structure with a purity of 99.99 % were used. The measurement of the admittance were carried out in a frequency range 1 Hz - 100 kHz on the devices FRA-1174 (Solartron Electronic Group) and interfaces ECI-1186. The purpose of our investigation was to apply the ac impedance spectroscopy to the study of physical properties of sulfur at pressures 20-50 GPa.