Resistivity relaxation of ammonium halides near high‐pressure induced phase transitions

Abstract

Comparative studies of high-pressure effect on the resistivity of ammonium halides NH 4 X (X = F, Cl, Br) at the temperatures of 77 to 400 K are presented. High-pressure phase transitions are found being apparent in a sharp change of the resistance by orders of magnitude at some critical pressures and a hysteresis typical for first-order phase transitions. The critical pressure values correlate with the material density being approximately 40, 27 and 15 GPa for NH 4 F, NH 4 Cl and NH 4 Br, respectively. Relaxation times of resistivity at changing pressure are determined. The relaxation of resistivity obeys the exponential law at the pressures far enough from the critical ones; the relaxation times are tenths seconds to minutes. Near the critical pressures, the resistivity relaxation becomes highly non-exponential; the time delay of hours to days appears before the phase transition (the resistance jump).