The effect of electric field threshold switching from high resistivity to low resistivity state in ceramic samples of CuCr1–xAlxO2 delafossite solid solutions

Abstract

Samples of the CuCr_1-xAl_xO₂ system with x = 0, 0.25, 0.5, 0.75, 1 were synthesized using conventional ceramic technology. X-ray diffraction phase analysis data indicate the formation of an unlimited solid solution in the system with the delafossite crystal structure (a = 2.97–2.95 Å, c = 17.1–16.9 Å, sp. gr. R-3 m). Scanning electron microscopy data show that in samples with x = 0.25, 0.5, 0.75, particles of large and small sizes are embedded into each other. The calculated average grain sizes of the samples vary from 1.2 to 7.5 µm. The temperature dependencies of the electrical resistance of the samples under direct current were studied in the temperature range from 77 to 300 K with electric field strengths of 0.001, 0.94, 1.27, and 1.5 kV/cm. The current–voltage characteristics of the samples were studied in the range of electric field strengths up to 4.5 kV/cm at temperatures of 120, 175, and 220 K. It was established that the application of a constant electric field of 0.94, 1.27, and 1.5 kV/cm leads to switching from a high resistance state to a low resistance state. This switching is manifested in the form of giant resistance jumps (up to six orders of magnitude) in the temperature range of 90–200 K, as well as in the form of S-shaped volt-ampere characteristics containing a region of negative differential resistance. An interpretation of the observed switching effect is provided based on the polaron mechanism of conductivity.