INFLUENCE OF CATION SUBSTITUTION ON THE ELECTRICAL CONDUCTIVITY OF SUPERIONIC CERAMICS BASED ON MICROCRYSTALLINE POWDERS OF (Cu1−xAgx)7SiS5I

Abstract.

Purpose. The purpose of this research was to prepare the superionic ceramics, to study the frequency and temperature dependences of electrical conductivity as well as to investigate the compositional behavior of the total electrical conductivity, the ionic and electronic components of the electrical conductivity, and their activation energies for ceramics based on (Cu1−xAgx)7SiS5I solid solutions. Methods. For preparing the ceramic samples the compounds based on Cu7SiS5I, Ag7SiS5I and (Cu1−xAgx)7SiS5I (x = 0.25, 0.5, 0.75) solid solutions were synthesized. Then, the microcrystalline powders were obtained by grinding the synthesized compounds in an agate mortar to a sizes of ∼ 10-50 µm. Pressing of the samples was performed at a pressure of ∼ 400 MPa, and annealing was carried out at a temperature of 973 K during 36 hours. Ceramic samples based on (Cu1−xAgx)7SiS5I solid solutions were obtained in the form of disks with a diameter of 8 mm and a thickness of 3-4 mm. Investigations of the electrical conductivity of ceramics based on (Cu1−xAgx)7SiS5I (x = 0.25, 0.5, 0.75, 1) was performed by the method of impedance spectroscopy, in frequency (10 Hz – 2×106 Hz) and temperature (292-383K) ranges using the high-precision LCR meter Keysight E4980A and AT-2818. Measurement was carried out by a two-electrode method on blocking gold contacts, which were applied by chemical precipitation from solutions. Results. The frequency dependences of the total electrical conductivity showed an increase of conductivity with increasing frequency for all ceramic samples. It has been established that with increasing Ag content in ceramics based on (Cu1−xAgx)7SiS5I, the total electrical conductivity is growing non-linearly at 100 kHz. Nyquist diagrams were constructed and their detailed analysis was carried out using an electrodes-equivalent circuit. Using the Nyquist diagrams and the electrodes-equivalent circuit, the contributions of the ionic and electronic components to the total electrical conductivity were separated. It is shown that with silver content increase the ionic conductivity nonlinearly increases while the electronic conductivity nonlinearly decreases. The analysis of the compositional dependence of the ratio of the ionic conductivity to the electronic one showed that due to the cation substitution of Cu+ → Ag+ the ratio nonlinearly increases. Conclusions. Superionic ceramics based on (Cu1−xAgx)7SiS5I were prepared. Measurements of electrical conductivity of ceramic samples by means of impedance spectroscopy in the frequency range from 10 Hz to 2×106 Hz and in the temperature range 292-383 K were carried out. Frequency dependencies of total electrical conductivity were obtained. The influence of the cation substitution of Cu+ → Ag+ on the total electrical conductivity, on the electronic and ionic components of the conductivity of ceramics based on (Cu1−xAgx)7SiS5I was studied on the basis of compositional dependences

Keywords: solid solutions, ceramic, electrical conductivity, activation, compositional dependence

https://doi.org/10.24144/2415-8038.2020.47.21-31