High P-T Electrical Impedance Spectroscopy Measurement on SrTiO₃ Using the Paris-Edinburgh Press at HPCAT

Studies of material properties using X-ray diffraction at high-pressure (P) and temperature (T) conditions using the large volume Paris-Edinburgh (PE) press at HPCAT 16BMB has advanced our knowledge of materials behavior at extreme conditions. With P and/or T, materials property can be tuned as the interatomic distances change. Perovskite materials (ABO₃) have interesting properties as they can lose or perhaps regain their ferroelectricity with changes in P and T. Electrical Impedance Spectroscopy (EIS) can probe such change by measuring the frequency-dependent AC impedance response in range of kilo- to mega-ohms. Using an offline EIS setup that is established for ultimate integration into 16BMB, we investigated the electrical properties of SrTiO₃ at high P up to 4.7 GPa and T up to 1050 K. With increasing T, at a fixed P of 1.8, 3.2 and 4.7 GPa, our result shows a sharp drop in the total impedance from approximately 10 mega-ohms to about 1 mega ohm at ~543 K which suggest a phase transformation. The formation of semi-circular pattern in the Nyquist plot was not observed when the total impedance stays within the order of 10 mega-ohms before the observed drop, which shows the materials acts as an insulator. However, at T above the transition, a semi-circular pattern was observed in the Nyquist plot, which indicates the materials transport property has transformed to a dielectric. The corresponding capacitance was estimated by fitting an equivalent circuit model. Our results will be used to map the phase diagram of SrTiO₃ at extreme conditions and demonstrate that the results could provide additional insight into the general behavior of the class of materials.