Abstract

Purpose. The purpose of this study 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 (Cu_1−xAg_x )₇SiS₅I solid solutions.

Methods. For preparing the ceramic samples the compounds on the basis of Cu₇ SiS₅ I, Ag₇ SiS₅ I and (Cu_1−xAg_x)₇SiS₅I (x = 0.25, 0.5, 0.75) solid solutions were synthesised. Then, microcrystalline powders have been manufactured with the help of grinding/disintegration of the synthesised compounds within the agate mortar down to the sizes approximately from 10 up to 50 µm. Pressing of the samples was performed at the pressure of approximately 400 MPa, while annealing was carried out at the temperature of 973ºK during 36 hours. Ceramic samples [which were manufactured on the basis of the (Cu_1−xAg_x)₇SiS₅I solid solutions] were manufactured in the form of disks having diameters at the level of 8 mm and thicknesses at the level from 3 mm up to 4 mm. Investigations of the electrical conductivity of the ceramics on the basis of the (Cu_1−xAg_x)₇SiS₅I (x = 0.25, 0.5, 0.75, 1) were performed with the help of the impedance spectroscopy method within the range of frequencies from 10 Hz up to 2×10⁶ Hz, as well as within the range of temperatures from 292ºK up to 383ºK with the help of the following highly-precision LCR meters: Keysight E4980A and AT-2818. Measurements were performed in accordance with the two-electrode method on the blocking golden contacts, which have been applied with the help of the method of chemical precipitation from the relevant solutions. 

Results. Frequency dependences of the total electrical conductivity have demonstrated an increase in the conductivity in the course of increase in frequency for all ceramic samples. It was established that in the course of increase in the silver content in the ceramics on the basis of the (Cu_1−xAg_x)₇SiS₅I, general electrical conductivity increases nonlinearly at 100 kHz. Nyquist diagrams were constructed and their detailed analysis was carried out using the electrode equivalent circuits. With the help of the Nyquist diagrams and the electrode equivalent circuits, contributions of the ionic and electronic components to the general electrical conductivity were determined. It was demonstrated that in the course of the increase in silver content, the ionic conductivity increases nonlinearly, while the electronic conductivity nonlinearly decreases. Analysis of the concentration dependence of the ratio of the ionic conductivity to the electronic one has shown that in the case of the cation substitution (Cu⁺→ Ag⁺), this ratio nonlinearly increases. 

Conclusions. Superionic ceramics on the basis of the (Cu_1−xAg_x)₇SiS₅I were prepared. Measurements of electrical conductivity of the ceramic samples with the help of the impedance spectroscopy method within the range off requencies from 10 Hz to 2×10⁶ Hz, as well as within the range of temperatures from 292ºK up to 383ºK were performed. Frequency dependences of general electrical conductivity were obtained. Influence of the cation substitution (Cu⁺→ Ag⁺) upon the general electrical conductivity and upon the electronic and ionic components of the conductivity of ceramics on the basis of the (Cu_1−xAg_x)₇SiS₅ was studied on the basis of concentration dependences

Keywords: solid solutions, ceramics, electrical conductivity, energy of activation, concentration dependence

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