Various compositions in the system of A-site deficient perovskite (Y0.08Sr0.92)1-xTi0.6Fe0.4O3-δ (x = 0.05, 0.07, 0.10) was synthesized at 1350 °C in air by sol-gel method. The effects of A-site deficiency in (Y0.08Sr0.92)1-xTi0.6Fe0.4O3-δ on the phase structure, electrical conductivity and ionic conductivity have been investigated. Crystal structure remains cubic perovskite among the all compositions, which means Y, Fe co-doping and A-site deficiency do not negatively affect the formation of cubic perovskite structure. Partial oxygen ionic conductivity decreases with A-site deficiency amount increasing, which may be attributed to the tendency for oxygen vacancy ordering. The n-type electronic conduction in air increases with A-site deficiency amount increase. The behavior should be attributed to the decrease of [Fe′Ti][Fe′Ti] and [h][h] due to the possible ionization reaction of ferric iron. The total electrical conductivity of (Y0.08Sr0.92)1-xTi0.6Fe0.4O3-δ (x = 0.05, 0.07, 0.10) varies from 0.11 S·cm−1 to 0.26 S·cm−1 at 800 °C and the ionic conductivity varies from 0.012 S·cm−1 to 0.022 S·cm−1 at 900 °C.

Silico-ferrite of calcium (SFC) is a key intermediate phase in the sintering process of fine iron ores, and SiO2 plays an important role in the formation of SFC. In this work, the crystal structure stability of SFC synthesized at 1473 K (1200 °C) has been determined by X-ray diffraction, field-emission scanning electron microscopy, and X-ray absorption spectra. Synthesis of SFC was carried out under air at 1473 K (1200 °C) by mixing different amounts of SiO2 with Fe2O3 and CaCO3. The results show that the maximum solid solubility of SiO2 in the crystal structure of SFC does not exceed 6.11 wt pct at 1473 K (1200 °C); under these conditions, Fe2O3 begins to appear. The process of Si solution is closely related to the presence of a Ca channel composed of Ca octahedron in the crystal structure of SFC based on the results from the measurements of Ca K-edge X-ray absorption spectra. Si mainly occupies the center positions of the upper and lower tetrahedron adjacent to Ca channel. The length of Ca-Ca bond in Ca channel increases with the increasing of Si content. The crystal structure stability of SFC may be related to the structure of the Ca channel.

•A single cubic perovskite structure of YxSr1−xTi0.6Fe0.4O3−δ (x=0.07, 0.08, 0.09) powders was synthesized by the sol–gel method.•The doping limit of Y in the material is less than 10 mol%.•The Y-doping can improve the ionic conductivity of YxSr1−xTi0.6Fe0.4O3−δ.A single phase perovskite, YxSr1−xTi0.6Fe0.4O3−δ (x=0.07, 0.08, 0.09), was synthesized at 1350 °C by the sol–gel method. The effects of Y-doping on the electronic and ionic conductivities of YxSr1−xTi0.6Fe0.4O3−δ were investigated. The ionic conductivity of SrTiO3-based materials can be significantly improved by Y-doping on the A-site and Fe-doping on the B-site. We report in this paper a remarkable enhancement of ionic conductivity of Y, Fe co-doped SrTiO3 by the increase in Y-doping amount on the A-site. The total electrical conductivity and ionic conductivity were 0.135 S/cm and 0.017 S/cm for Y0.07Sr0.93Ti0.6Fe0.4O3−δ at 800 °C, respectively, while were 0.056 S/cm and 0.02 S/cm for Y0.09Sr0.91Ti0.6Fe0.4O3−δ.

•Confirmed the aging behavior in CaO excess calcium zirconate perovskite ceramics•The aging behavior works more seriously as temperature rises.•The Ca1.1Zr0.9O2.9 presents a much more stable conductivity than the 8.5 YSZ shows.•The annealing operation enforces the formation of association [CaZr″ − VO••] and makes oxygen vacancy trapped.•The lock of oxygen vacancy reduces its effective diffusion coefficient.A CaO excess type calcium zirconate electrolyte with a composition of Ca1.1Zr0.9O2.9 was prepared. Its aging behavior at 900 °C and 1100 °C was evaluated by AC impedance. The conductivity decreases more seriously at higher temperature. Combined with the aging effect of 8.5 YSZ, the formation of [CaZr″ − VO••] promoted by annealing operation should be responsible for the aging effect in Ca1.1Zr0.9O2.9. The declined mobility of VO•• is viewed as the increase in hopping activation energy and the decrease in effective concentration of VO••. Consequently, the diffusion coefficient of VO•• decreases and results in the aging behavior.

•A single cubic phase perovskite (Y0.08Sr0.92)1−xTi0.6Fe0.4O3−δ (x=0, 0.03, 0.05) was fabricated at 1350 °C by the sol–gel method.•A-site deficiency improved the total electrical conductivity of (Y0.08Sr0.92)1−xTi0.6Fe0.4O3−δ (x=0, 0.03, 0.05).•A-site deficiency enhanced the densification process of Y, Fe co-doped SrTiO3 materials, which promoted the chemical and electrical stability.•The possible charge compensation mechanism was concerned.Mixed ionic–electronic conductors with high electrical conductivity have an important effect on modern electrochemical devices. As a mixed ionic–electronic conductor, a single cubic phase perovskite (Y0.08Sr0.92)1−xTi0.6Fe0.4O3−δ (x=0, 0.03, 0.05) was fabricated at 1350 °C in air by the sol–gel method. The total electrical conductivity of SrTiO3-based materials can be significantly enhanced by deficiency of A-site and acceptor-doping on B-site. In the paper, a remarkable enhancement of total electrical conductivity and sinterability of A-site deficient (Y, Fe) co-doped SrTiO3 is reported. In addition, the possible charge compensation mechanism of A-site deficient Y, Fe co-doped SrTiO3 can be described as (Y0.08Sr0.92)1−xFe0.4Ti4+0.92(1−x)−0.4Ti3+0.08(1−x)O3−(δ+0.4/2) or (Y0.08Sr0.92)1−xFe0.4Ti4+0.92(1−x)−y1Ti3+0.08(1−x)−y2O3−(δ+y1/2) (y1+y2=0.4).

ZrOCl2·8H2O and ZrO(NO3)2·2H2O were used respectively to synthesize a NASICON solid electrolyte by a sol-gel method. The structure and properties of two samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The crystal structure was investigated by the Rietveld refinement. It is found that both the samples contain a monoclinic C2/c phase as the main conductive phase with the lattice parameters of a=1.56312 nm, b=0.90784 nm and c=0.92203 nm, though a small amount of rhombohedral phase is also detected in the final product. The sample synthesized by ZrO(NO3)2·2H2O contains more monoclinic phase (89.48wt%) than that synthesized by ZrOCl2·8H2O (74.91wt%). As expected, the ionic conductivity of the latter is higher than that of the former; however, the activation energy of the latter (0.37 eV) is slightly higher than that of the former (0.35 eV).

•The formation mechanism of SFC by solid-state reactions has been explained.•Initial product of SiO2 that participated in the formation of SFC was 2CaO·SiO2.•2CaO·SiO2 mainly formed by the reaction of SiO2 and CaO·Fe2O3.•2CaO·SiO2 that disappeared with it reacted with Fe2O3 and CF respectively to form SFC.•These will help in improving the understanding of SiO2 role in the formation of SFC.Silico-ferrite of calcium (SFC) is a key transitional phase in the formation process of complex silico-ferrites of calcium and aluminum (SFCA-Ι and SFCA), and SiO2 plays an important role in the formation of SFC. To study the formation mechanism of SFC by solid-state reactions is conducive to understanding the process of SiO2 involved in the formation of SFCA-I and SFCA. Experiments were carried out under air at different temperatures from 600 °C to 1200 °C by a certain amount of SiO2 mixing with Fe2O3 and Ca(OH)2. X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used to characterize the phase change of the sintered samples. The results show that the initial product of SiO2 that participated in the formation process of SFC is 2CaO·SiO2 (C2S) that mainly forms by the reaction of SiO2 and CaO·Fe2O3 (CF) at approximately 1000 °C. Subsequently, C2S that disappears with it reacts with Fe2O3 and CF respectively to form SFC at approximately 1100 °C. The reaction of C2S and Fe2O3 is more easily to occur compared with C2S and CF through the thorough solid-state reaction experiments between C2S, Fe2O3, and CF, and the formation of SFC will be promoted by the co-existence of Fe2O3 and CF that the optimal mole ratio of Fe2O3 to CF is approximately 1.00:0.55. Finally, melt appears at approximately 1200 °C due to the effect of the eutectic structure composed of SFC and CF.