The effect of Sr-nonstoichiometry on phase composition, microstructure, defect chemistry and electrical conductivity of Sr_xZrO_3−δ and Sr_xZr_0.95Y_0.05O_3−δ ceramics (SZx and SZYx, respectively; x = 0.94–1.02) was investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and impedance spectroscopy followed by distribution of relaxation times analysis of impedance data. It was shown that at low Sr deficiency (x > 0.96 and 0.98 for SZx and SZYx, respectively) a solid solution of strontium vacancies in strontium zirconate crystal structure forms, whereas at higher Sr deficiency the secondary phase, zirconium oxide or yttrium zirconium oxide, is precipitated. Yttrium solubility limit in strontium zirconate was found to be close to 2 mol%. Y-doped strontium zirconates possess up to two orders of magnitude higher total conductivity than SZx samples. A-site nonstoichiometry was shown to have a significant effect on the electrical conductivity of SZx and SZYx. The highest total and bulk conductivity were observed at x = 0.98 for both systems. Increasing the conductivity with a rise in humidity indicates that proton conduction appears in the oxides in wet conditions. A defect model based on consideration of different types of point defects, such as strontium vacancies, substitutional defects and oxygen vacancies, and assumption of Y ions partitioning over Zr and Sr sites was elaborated. The proposed model consistently describes the obtained data on conductivity.

The effect of Sr-deficiency on microstructure, phase composition and electrical conductivity of Sr_xZr_0.95Yb_0.05O_3-δ (x = 0.94–1.00) was investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and impedance spectroscopy. The samples were synthesized by a chemical solution method and sintered at 1600 °C. According to X-ray diffraction data, the samples with x = 0.96–1.00 were single-phase oxides possessing an orthorhombic perovskite-type structure; while zirconia-based minor phases arouse at x = 0.94, which was confirmed by the electron microscopy. Sr stoichiometry was shown to influence the electrical conductivity. The highest total and bulk conductivities, 6–10⁻⁴ Scm⁻¹ and 3–10⁻³ Scm⁻¹, respectively, at 600 °C in humid air (pH₂O = 3.2 kPa), were observed for the x = 0.98 composition. In the temperature range of 300–600 °C, the conductivity of the samples with x = 0.96–1.00 increased with the increase in humidity, which indicates a significant contribution of protonic defects to the charge transport. Electrical conductivity of Sr_xZr_0.95Yb_0.05O_3-δ was discussed in terms of the defect formation model and the secondary phases precipitation.

The effect of Sr deficiency on the hydration process and ionic and electronic conductivity of Yb-doped SrZrO₃ proton conductors with a perovskite-type structure was investigated. Dense Sr_xZr_0.95Yb_0.05O_3-δ (x = 0.94–1.00) ceramics were prepared using solution combustion synthesis. Thermogravimetry and Raman spectroscopy methods were used to determine the concentration of bulk protonic species. Sr deficiency was found to enhance the hydration ability of the zirconate; however, lowering of Sr content to x = 0.94 deteriorated the proton uptake. The conductivity of the Sr_xZr_0.95Yb_0.05O_3-δ series depending on the oxygen partial pressure at different humidities was studied by the four-probe direct current technique. Sr-deficient ceramics with x = 0.96 and 0.98 were shown to become purely protonic conductors in humid atmospheres at a temperature close to 500 °C. The ionic conductivity reaches its highest value at a Sr content of x = 0.98 (2 × 10⁻⁴ S cm⁻¹ at 500 °C and pH₂O = 3.17 kPa). The hydration behavior and transport properties of Sr_xZr_0.95Yb_0.05O_3-δ are discussed in terms of the defect chemistry model that assumes the distribution of Yb ions over Sr and Zr sites at a large Sr deficiency.

Layered lanthanide nickelates Ln2NiO4+δ are considered as potential cathode materials in solid oxide fuel cells. In this study, the chemical stability, thermal expansion and electrical conductivity of a number of layered nickelates, namely Lа2NiO4+δ, Pr1.7Sr0.3NiO4+δ, Pr1.7Ca0.3NiO4+δ and Nd1.9Ca0.1NiO4+δ, are investigated. Based on the chemical stability, thermal expansion and electrical conductivity studies, the composite material consisting of Pr1.7Ca0.3NiO4+δ and Sr0.98Zr0.95Yb0.05O3–δ oxides (PCN-SZYb) was selected as a suitable oxygen electrode for the proton-conducting Sr0.98Zr0.95Yb0.05O3–δ electrolyte. The electrochemical behavior of the electrolyte-supported cells with the symmetrical porous PCN-SZYb electrodes was investigated in air with different humidities in the temperature range of 350–800 °C. The impregnation of a porous electrode backbone with the praseodymium nitrate solution enhanced the activity of the electrodes by approximately 3 times. The electrochemical behavior of the composite electrode in contact with the Sr0.98Zr0.95Yb0.05O3–δ electrolyte is consistent with the literature data on the Ln2NiO4+δ-based electrodes and related proton-conducting electrolytes.

Phase composition, thermal expansion, and electrical conductivity were studied for three-component solid solutions of the system HfO₂–Sc₂O₃–Y₂O₃, containing 7–10 mol % Sc₂O₃ and 1–4 mol % Y₂O₃, which corresponds to the maximum-conductivity region. The electrical conductivity was measured in two ways: by the four-probe mode in the dc mode and by impedance spectroscopy. A solid electrolyte of composition HfO₂ + 8 mol % Sc₂O₃ + 2 mol % Y₂O₃ was obtained, close in conductivity to the solid electrolyte composed of ZrO₂ + 8 mol % Y₂O₃.

The effect of isovalent substitution of hafnium by tin in strontium hafnate on sinterability and electrical conductivity was studied for the first time. The ceramic samples SrHfxSn1–xO3–δ (x = 0–0.16) were synthesized by solid-state reaction and sintered at 1600 °C for 5 h. The samples were examined using the methods of X-ray diffraction, scanning electron microscopy, impedance spectroscopy, and four-probe direct current technique. It was shown that all samples were phase pure and had the orthorhombic structure of SrHfO3 with the Pnma space group. Sn doping resulted in an increase in grain size, relative density and conductivity; the sample with x = 0.08 demonstrated the highest conductivity, which was ~830 times greater than that of undoped strontium hafnate at 600 °C. The conductivity of SrHf0.92Sn0.08O3–δ was 4.1∙10–6 S cm–1 at 800 °C in dry air. The possible reasons for the effect of Sn on the electrical properties of strontium hafnate were discussed.