Raman and Si NMR spectroscopic characterization of lanthanum silicate electrolytes: Emphasis on sintering temperature to enhance the oxide-ion conductivity

Enhancement of oxide-ion conductivity has been investigated with emphasis on the high sintering temperature of apatite-type structure lanthanum silicate (La₁₀Si₆O₂₇) as a potential electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The influence of the sintering temperatures 1500, 1550, 1600 and 1650 °C as a function of ionic conductivity of the La₁₀Si₆O₂₇ electrolyte synthesized via a diethylamine (DEA) precipitation process has been characterized using impedance spectroscopy. The ionic conductivity of the La₁₀Si₆O₂₇ electrolyte sintered at 1650 °C revealed a higher value (1.22 × 10⁻² S cm⁻¹ at 700 °C) of one order of magnitude than the pellets sintered at lower temperatures. The sintered La₁₀Si₆O₂₇ pellets have been characterized by ²⁹Si NMR and Raman spectroscopy. The ²⁹Si NMR data showed the characteristic secondary peak at 81.2 ppm, which confirmed the interstitial oxygen content contributing to high oxide-ion conduction. The Raman spectra revealed the appearance of a new resolved band centered at 861 cm⁻¹ for the pellet sintered at 1650 °C compared with lower temperatures sintered pellets. The results confirmed the possibility of local structural distortion to create additional pathways for interstitial oxide-ion conduction between channels leading to higher conductivity for the pellets sintered above 1600 °C. Thus, the conduction pathway may be determined by the co-operative displacements of the SiO₄ substructure units formed at elevated sintering temperatures for high oxide-ion conductivity.     

Synthesis of Ga-doped Li7La3Zr2O12 solid electrolyte with high Li+ ion conductivity

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) Li⁺ ion solid electrolyte is a promising candidate for next generation high-safety solid-state batteries. Ga-doped LLZO exhibits excellent Li⁺ ion conductivity, higher than 1 × 10^?3 S cm^?1. In this research, the doping amount of Ga, the calcination temperature of Ga-LLZO primary powders, the sintering conditions and the evolution of grains are explored to demonstrate the optimum parameters to obtain a highly conductive ceramics reproducibly via conventional solid-state reaction methods under ambient air sintering atmosphere. Cubic LLZO phase is obtained for Li_6.4Ga_0.2La₃Zr₂O₁₂ powder calcined at low temperature 850 °C. In addition, ceramic pellets sintered at 1100 °C for 320 min using this powder have relative densities higher than 94% and conductivities higher than 1.2 × 10^?3 S cm^?1 at 25 °C.     

Influence of dry- and wet-milled LLZTO particles on the sintered pellets

A Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO) solid electrolyte is a promising candidate for all-solid-state lithium battery due to its high ionic conductivity and stability against lithium metal. In this work, physicochemical properties of both dry- and wet-milled LLZTO particles were investigated. Based on X-ray diffraction, Fourier transform–infrared, thermogravimetric analysis, and scanning electron microscopy results, it was confirmed that highly reactive LLZTO powder prepared in dry milling conditions exhibited faster size reduction, rougher surface morphology, fewer surface impurities, and less agglomerated particles, in contrast to those in wet milling conditions. Sintering these dry-milled powders at 1320°C for 10 min in the air via solid-state reaction produced dense ceramic pellets with a relative density of 97.4%. The room-temperature ionic conductivity for LLZTO pellet via the dry milling was determined to be 6.94 × 10⁻⁴ S cm⁻¹. Li–sulfur batteries based on the pellets showed an initial discharge capacity of 1301 mA h g⁻¹ and a coulombic efficiency of 99.82% when cycled at room temperature. The effect of the milled powder on the sintered pellets was discussed in terms of boundary mobility, pore mobility, and morphology.     

Influence of processing conditions on the ionic conductivity of holmium zirconate (Ho2Zr2O7)

Nanopowders of holmium zirconate (Ho₂Zr₂O₇) synthesised through carbon neutral sol-gel method were pressed into pellets and individually sintered for 2 h in a single step sintering (SSS) process from 1100 °C to 1500 °C at 100 °C interval and in a two step sintering (TSS) process at (I) −1500 °C for 5 min followed by (II) - 1300 °C for 96 h. Relative density of each of the sintered pellet was determined using the Archimedes’ technique and the theoretical density was calculated from crystal structure data. Grain size was obtained from SEM micrographs using ImageJ. Pellets processed by TSS have been found to be denser (98 %) with less grain growth (1.29 μm) as compared to the pellets processed using SSS process. Ionic conductivity of Ho₂Zr₂O₇ pellets sintered by two different processes was measured using ac impedance spectroscopy technique over the temperature range of 350 °C–750 °C in the frequency range of 100 mHz–100 MHz for both heating and cooling cycles. The temperature dependence of bulk (2.67⨯10⁻³ Scm⁻¹) and grain boundary (2.50⨯10⁻³ Scm⁻¹) conductivities of Ho₂Zr₂O₇ prepared by TSS process are greater than those processed by SSS process suggesting the strong influence of processing conditions and grain size. Results of this study, indicates that the TSS is the preferable route for processing the holmium zirconate as it can be sintered to exceptionally high densities at lower temperature, exhibits less grain growth and enhanced ionic conductivity compared with the samples processed by SSS process. Hence, holmium zirconate can be considered as a promising new oxide ion conducting solid electrolyte for intermediate temperature SOFC applications between 350 °C and 750 °C temperature range.     

Structural (in)stability and spontaneous cracking of Li-La-zirconate cubic garnet upon exposure to ambient atmosphere

Among the Li-ion conducting inorganic materials, lithium lanthanum zirconate (LLZO) is believed to possess good chemical stability against Li metal and hence considered to be a promising solid electrolyte for Li-ion batteries. However, systematic sets of studies conducted here at regular intervals during storage of Al-doped LLZO (cubic garnet) sintered pellets in ambient atmosphere have raised serious concerns over their structural/mechanical stability/integrity upon exposure to air. Spontaneous cracking/disintegration/pulverization of LLZO pellets takes place after about three weeks of exposure, primarily due to formation of La₂Zr₂O₇ in the LLZO bulk; as found to be thermodynamically feasible at room temperature upon reaction with CO₂/moisture. Steep increase in La₂Zr₂O₇ content coincides with the spontaneous cracking/disintegration. Estimation suggests that internal stresses associated with the formation of La₂Zr₂O₇ from LLZO can be high enough to cause spontaneous fracture. This mandates the development/fabrication/usage of solid-state cells using LLZO under stringent controls against exposure to atmospheric species.     

Improved structural stability and ionic conductivity of Na3Zr2Si2PO12 solid electrolyte by rare earth metal substitutions

Sodium zirconium silicon phosphorus with the composition of Na₃Zr₂Si₂PO₁₂ (NZSP) was prepared by a facile solid state reaction method. The effects of the calcination temperature and rare earth element substitution on the structure and ionic conductivity of the NZSP material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and AC impedance measurement. The results show that the microstructure and ionic inductivity of the NZSP was strongly affected by the aliovalent substitution of Zr⁴⁺ ions in NZSP with rare earth metal of La³⁺, Nd³⁺ and Y³⁺. At room temperature, the optimum bulk and total ionic conductivity of the pure NZSP solid electrolyte sintered under different conditions were 6.77×10⁻⁴ and 4.56×10⁻⁴ S cm⁻¹, respectively. Substitution of La³⁺, Nd³⁺ and Y³⁺ in place of Zr⁴⁺ exhibited higher bulk conductivity compared with that of pure NZSP. Maximum bulk and ionic conductivity value of 1.43×10⁻³ and 1.10×10⁻³ S cm⁻¹ at room temperature were obtained by Na_3+xZr_1.9La_0.1Si₂PO₁₂ sample. The charge imbalance created by aliovalent substitution improves the mobility of Na⁺ ions in the lattice, which leads to increase in the conductivity. AC impedance results indicated that the total ionic conductivity strongly depends on the substitution element and the feature of the grain boundary.     

A novel promotion strategy for microstructure and electrical performance of garnet electrolytes via Li4GeO4 additive

Cubic Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (c-LLZTO) electrolyte is one of the most promising solid electrolytes. However, it is rather difficult to promote its electrical performance while reducing process parameters. Therefore, Li₄GeO₄ is applied as the additive in liquid sintering of LLZTO ceramics in this study. The LLZTO@Li₄GeO₄/Li₂O composite electrolyte sintered at 1180 °C for 3 h performs a significantly promoted microstructure and electrical performance, the ionic conductivity of which reaches 5.77 × 10⁻⁴ S cm⁻¹ at 25 °C. The Li₄GeO₄/Li₂O eutectic phase contributed prominently, in which the high concentration of Li⁺ seaming the LLZTO grains tightly. Meanwhile, Li⁺ conduction in the consecutive conductive pathways constructed by [GeO₄] groups among the grains was greatly stimulated. With the modification of the grain boundary, an improved garnet electrolytes/Li anode interface performance is produced. The Li/Au|LLZTO@Li₄GeO₄/Li₂O|Au/Li symmetrical cell is able to cycle stably for more than 500 h at the current density of 0.1 mA cm⁻² at room temperature.     

High Li-ion conductivity of Al-doped Li7La3Zr2O12 synthesized by solid-state reaction

Li₇La₃Zr₂O₁₂ (LLZO) has cubic garnet type structure and is a promising solid electrolyte for next-generation Li-ion batteries. In this work, Al-doped LLZO was prepared via conventional solid-state reaction. The effects of sintering temperature and Al doping content on the structure and Li-ion conductivity of LLZO were investigated. The phase composition of the products was confirmed to be cubic LLZO via XRD. The morphology and chemical composition of calcined powders were investigated with SEM, EDS, and TEM. The Li-ion conductivity was measured by AC impedance. The results indicated the optimum sintering temperature range is 800–950 °C, the appropriate molar ratio of LiOH·H₂O, La(OH)₃, ZrO₂ and Al₂O₃ is 7.7:3:2:(0.2–0.4), and the Li-ion conductivity of LLZO sintered at 900 °C with 0.3 mol of Al-doped was 2.11×10⁻⁴ S cm⁻¹ at 25 °C.     

Dense 8 mol% yttria-stabilized zirconia electrolyte by DLP stereolithography

Solid Oxide Fuel Cells (SOFCs) are environmentally efficient energy conversion devices, but are partially limited by the complicated fabrication procedure. In this work, dense 8 mol% yttria-stabilized zirconia (8YSZ) ceramics were successfully realized through a DLP (digital light processing) stereolithography method and the electrolyte self-supported fuel cell was also tested at 800 °C. The sintering behavior of the as-printed planar samples were investigated and a fully dense ceramic can be achieved at 1450 °C. The total conductivity of the sintered 8YSZ can reach 2.18 × 10⁻² S cm⁻¹ at a test temperature of 800 °C, which is acceptable for practical application. For the electrolyte self-supported fuel cell test, a power density of 114.3 mW cm⁻² can be achieved when Ni-8YSZ cermet and La_0.8Sr_0.2MnO₃ (LSM) were used as anode and cathode. It was demonstrated that 3D printing is a promising processing technique to build up electrolyte self-supported SOFCs with desired structure for the future development.     

Fabrication and Performance of Solid Oxide Fuel Cells with La0.2Sr0.7TiO3–δ as Anode Support and La2NiO4+δ as Cathode

A novel fabrication process for solid oxide fuel cells (SOFCs) with La_0.2Sr_0.7TiO_3–δ (LST_A–) as anode support and La₂NiO_4+δ (LNO) as cathode material, which avoids complicated impregnation process, is designed and investigated. The LST_A– anode‐supported half cells are reduced at 1,200 °C in hydrogen atmosphere. Subsequently, the LNO cathode is sintered on the YSZ electrolyte at 1,200 °C in nitrogen atmosphere and then annealed in situ at 850 °C in air. The results of XRD analysis and electrical conductivity measurement indicate that the structure and electrochemical characteristics of LNO appear similar before and after the sintering processes of the cathode. By using La_0.6Sr_0.4CoO_3–δ (LSC) as current collector, the cell with LNO cathode sintered in nitrogen atmosphere exhibits the power density at 0.7 V of 235 mW cm⁻² at 800 °C. The ohmic resistance (R_S) and polarization resistance (R_P) are 0.373 and 0.452 Ω cm², respectively. Compared to that of the cell with the LNO cathode sintered in air, the sintering processes of the cell with the LNO cathode sintered in nitrogen atmosphere can result in better electrochemical performance of the cell mainly due to the decrease in R_S. The microstructures of the cells reveal a good adhesion between each layer.     

Atmospheric plasma spraying to fabricate metal-supported solid oxide fuel cells with open-channel porous metal support

Metal-supported solid oxide fuel cells (MS-SOFCs) have been fabricated by applying phase-inversion tape-casting and atmospheric plasma spraying (APS). The effect of the binder amount of the phase-inversion slurries on the microstructure development of the 430L stainless steel metal support was investigated. The pore structures, the viscosity of the slurry, porosity and permeability of the as-prepared metal supports are significantly influenced by the amount of the binder. NiO–scandia-stabilized zirconia (ScSZ) anode, ScSZ electrolyte and La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) cathode layers were consecutively deposited on the metal support with an ideal microstructure by APS process. The effect of plasma power of the APS on the microstructure of the electrolyte and cathode was investigated. A dense electrolyte layer and a porous cathode layer were successfully obtained at 40 and 6 kW of the APS plasma power, respectively. MS-SOFCs, with a cell configuration of 430L/Ni-ScSZ/ScSZ/LSCF, achieved a maximum cell power density of 1079 mW cm⁻² at 700°C using humidified H₂ as fuel and ambient air as oxidant. The corresponding ohmic resistance and total resistance of MS-SOFCs was 0.14 and 0.32 Ω cm², respectively. This work demonstrates the feasibility of fabricating high-performance MS-SOFCs with economical and scalable techniques.     

The Influence of La Doping and Heterogeneity on the Thermoelectric Properties of Sr3Ti2O7 Ceramics

La‐doping mechanisms and thermoelectric properties of Sr₃Ti₂O₇ Ruddlesden–Popper (RP) ceramics sintered under air and flowing 5% H₂ at 1773 K for 6 h have been investigated. Changes in lattice parameters and conductivity revealed a limited interstitial anion mechanism (~1 at.%) based on La³⁺ + ½O^2?→Sr²⁺, which resulted in insulating samples when processed in air. In contrast, electronic donor‐doping (La³⁺ + e^? → Sr²⁺) and oxygen loss [O^2? → ½ O₂ (g) + 2 e^?] are the dominant mechanism(s) in 5% H₂‐sintered ceramics with a solution limit of ~5 at.%. The increased solubility limit is attributed to the formation of Ti³⁺ during reduction, which compensates for the extra positive charge associated with La on the A‐site and also to the occurrence of oxygen loss due to the reducing conditions. For 5% H₂‐sintered samples, an insulating surface layer was formed associated with SrO volatilization and oxygen uptake (during cooling) from the sintering. Unless removed, the insulating layer masked the conductive nature of the ceramics. In the bulk, significantly higher power factors were obtained for ceramics that were phase mixtures containing highly conductive perovskite‐based (Sr,La)TiO_3?δ (ST). This highlights the superior power factor properties of reduced perovskite‐type ST phases compared to reduced RP‐type Sr₃Ti₂O₇ and serves as a precaution for the need to identify low levels of highly conducting perovskite phases when exploring rare‐earth doping mechanisms in RP‐type phases.     

Structure,stability, and ionic conductivity of perovskite Li2x-ySr1-x-yLayTiO3 solid electrolytes

Solid electrolytes with high lithium-ion conductivity and superior stability are key components in the development of all-solid-state lithium-ion batteries. In this study, novel quaternary solid electrolytes Li_2x-ySr_1-x-yLa_yTiO₃ (x = 3y/4, y = 1/7, 2/7, 3/7, 1/2, 15/28, and 4/7) were synthesized by conventional solid-state reaction approach. X-ray diffraction analysis revealed that with the increase in La³⁺ content, Li_2x−ySr_1−x−yLa_yTiO₃ structure changes from cubic to tetragonal perovskite-type structure. Electrochemical impedance spectroscopy revealed that with the increase in y-value, enhanced conductivity was initial observed, followed by a decrease. Li_15/56Sr_1/16La_15/28TiO₃ electrolyte exhibited optimal total Li-ion conductivity of 4.84 × 10⁻⁴ S cm⁻¹, electronic conductivity of 6.84 × 10⁻¹⁰ S cm⁻¹, and activation energy of 0.29 eV. On the other hand, cyclic voltammetry revealed unstable Li_1/8Sr_1/8La_1/2TiO₃, Li_15/56Sr_1/16La_15/28TiO₃, and Li_2/7La_4/7TiO₃ specimens at voltages of less than ~2 V, indicative of their incompatibility with lithium metal or Li₄Ti₅O₁₂ in all-solid-state batteries. Charge-discharge tests confirmed the utility of electrolytes as solid separators with good performance in semi-solid-state batteries. Overall, these results are beneficial for future research on solid electrolytes and their applications in all-solid-state lithium-ion batteries.     

Sintering temperature dependency on sodium-ion conductivity for Na2Zn2TeO6 solid electrolyte

We investigated the sintering temperature dependency on the properties of Na₂Zn₂TeO₆ (NZTO) solid electrolyte synthesized via a conventional solid-state reaction method. Sintering temperature of calcined NZTO powder, which was obtained by the calcination of precursor at 850℃, was changed in the range from 650 to 850℃. X-ray diffraction analysis showed that P2-type layered NZTO phase was formed in all sintered samples without forming any secondary phases. The relative densities of sintered NZTO samples were approximately 83%−85% for the samples sintered at 700℃ or higher. The all sintered samples showed sodium-ion conductivity above 10⁻⁴ S cm⁻¹ at room temperature and the highest conductivity of 4.0 × 10⁻⁴ S cm⁻¹ in the sample sintered at 750℃. The sintering temperature to obtain the highest room temperature conductivity is 100℃ lower than that used in previous works. Such low sintering temperature compared to other Na-based oxide solid electrolytes could be useful for co-sintering with electrode active materials for fabrication of all-solid-state sodium-ion battery.     

Electrical characterization of La9.33Si2Ge4O26 oxyapatite for prospective intermediate-temperature solid oxide fuel cells

La_9.33Si₂Ge₄O₂₆ materials have been fabricated from La₂O₃, SiO₂ and GeO₂ powders by high speed mechanical alloying followed by conventional and microwave hybrid sintering at different temperatures and holding times. XRD data showed that the apatite phase is formed after 1 h of mechanical alloying at 850 rpm. This phase remained stable after conventional sintering in an electric furnace with density increasing as sintering temperatures and holding times were increased. However, the highest density was achieved for samples sintered in the microwave furnace (5.44 g cm⁻³), corresponding to a relative density of 98%. The electrical conductivity of the samples microwave sintered at 700 and 800 ºC are 4.72×10⁻³ and 1.93×10⁻² S.cm⁻¹, respectively, with a correspondent activation energy of 0.952 eV.     

A novel cobalt–free La0.5Ba0.5Fe0.95Mo0.05O3–δ electrode for symmetric solid oxide fuel cell

Cobalt − free perovskite oxide La_0.5Ba_0.5Fe_0.95Mo_0.05O_3−δ (LBFMo) was investigated as the electrode of symmetric solid oxide fuel cell (S − SOFC) based on 300−um − thick La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. The electrochemical performance of the S − SOFC with LBFMo|LSGM|LBFMo configuration was evaluated using ambient air as oxidant and H₂ as fuel. The maximum power density (P_max) of the S − SOFC achieves as high as 0.96 W cm⁻² at 800 °C; meanwhile, the total polarization resistance (R_pt) of the S − SOFC (including the contributions of both cathode and anode) is only ∼0.12 Ω cm². Impedance spectra analysis indicates the polarization associated with anode plays a more rate − limiting role in the whole electrochemical reaction process of the S − SOFC. In addition, using LBFMo as symmetric electrode, the S − SOFC also exhibits good cell stability. All results indicate that the LBFMo is a very potential candidate for S − SOFC electrode.     

Study of the ionic conductivity of Li0.5La0.5TiO3 laser-sintered ceramics

This work explores a chemical synthesis route and, for the first time, laser processing of ionic conductor Li_0.5La_0.5TiO₃ (LLTO) ceramics. The laser sintering technique has been efficient in producing highly dense single-phase ceramics in just a few minutes, starting from an amorphous precursor powder. As comparison, conventionally sintered ceramics were also prepared. Both methods yield polycrystals with long-range structure compatible with a single cubic perovskite, as confirmed by Rietveld refinement of the powder XRD pattern. In contrast, Raman spectroscopy has revealed non-cubic symmetry, indicating the formation of ordered nanodomains. At room temperature, high ionic conductivity of ∼0.5 mS/cm was achieved for the bulk of laser and conventionally sintered samples. However, the grain boundary conductivity changed from 1⋅10⁻³ mS⋅cm⁻¹ (laser-sintered) to 6⋅10⁻³ mS⋅cm⁻¹ (conventionally sintered), which was attributed to changes in the microstructural characteristics of the ceramics.     

MgO or Al2O3 crucible: Which is better for the preparation of LLZ-based solid electrolytes?

Lithium lanthanum zirconate (Li₇La₃Zr₂O₁₂, LLZ) solid electrolytes were usually prepared by using Al₂O₃ crucibles and/or Al³⁺ dopants in order to stablize the formation of cubic garnet phase. In this work, we argue that Al-free MgO crucible could be better for the preparation of LLZ-based solid electrolytes through a detailed comparison of LLZ-Ga_0.2 samples prepared respectively by using MgO and Al₂O₃ crucibles. The solid-state reaction method was firstly used to prepare Li_7-3xGa_xLa₃Zr₂O₁₂ (x = 0–0.4) pellets by using Al-free MgO crucibles, which were sintered at 1100 °C for 12 h. The highly conductive cubic phase was obtained at Ga³⁺ doping content as low as x = 0.05 and the highest room-temperature conductivity was obtained at x = 0.2. Al₂O₃ crucible was then used to prepare the LLZ-Ga_0.2 pellet for comparing the influence of these two different crucibles. The results show that a higher lattice parameter (a = 12.9762 (8) Å), a higher relative density (95.5%) and a higher room-temperature ionic conductivity (1.352 (3) mS/cm) were achieved by using the MgO crucible.     

Fabrication and Characterization of Anode‐Supported Low‐Temperature SOFC Based on Gd‐Doped Ceria Electrolyte

Large‐size, 9.5 cm × 9.5 cm, Ni‐Gd_0.1Ce_0.9O_1.95 (Ni‐GDC) anode‐supported solid oxide fuel cell (SOFC) has been successfully fabricated with NiO‐GDC anode substrate prepared by tape casting method and thin‐film GDC electrolyte fabricated by screen‐printing method. Influence of the sintering shrinkage behavior of NiO‐GDC anode substrate on the densification of thin GDC electrolyte film and on the flatness of the co‐sintered electrolyte/anode bi‐layer was studied. The increase in the pore‐former content in the anode substrate improved the densification of GDC electrolyte film. Pre‐sintering temperature of the anode substrate was optimized to obtain a homogeneous electrolyte film, significantly reducing the mismatch between the electrolyte and anode substrate and improving the electrolyte quality. Dense GDC electrolyte film and flat electrolyte/anode bi‐layer can be fabricated by adding 10 wt.% of pore‐former into the composite anode and pre‐sintering it at 1,100 °C for 2 h. Composite cathode, La_0.6Sr_0.4Fe_0.8Co_0.2O₃, and GDC (LSCF‐GDC), was screen‐printed on the as‐prepared electrolyte surface and sintered to form a complete single cell. The maximum power density of the single cell reached 497 mW cm^–2 at 600 °C and 953 mW cm^–2 at 650 °C with hydrogen as fuel and air as oxidant.     

Investigation on La3+ and Dy3+ co-doped ceria ceramics with an optimized average atomic number of dopants for electrolytes in IT-SOFCs

In the present study, we investigate the fundamental properties of CeO₂ by selecting La³⁺ (57), and Dy³⁺ (66) as dopants with optimized average atomic number of 61.5, which lies in between Pm³⁺ (62) and Sm³⁺ (62) in accordance with the criteria for optimum doping. A system of co-doped ceria ceramics Ce_1–x–yLa_xDy_yO_2-δ ((x, y) = (0.00, 0.00), (0.025, 0.025), (0.05, 0.05), (0.075, 0.075), (0.10, 0.10), (0.00, 0.20) and (0.20, 0.00)) as electrolytes for intermediate temperature solid oxide fuel cells were successfully prepared by a well-known sol-gel auto-combustion route. In order to obtain dense samples, the prepared pellets were sintered in air at 1300 °C for 4 h using conventional furnace and relative densities of all the samples were found to be higher than 95%. Single phase cubic structure, microstructural density and elemental composition analysis of all the samples were studied by powder X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy techniques, respectively. Raman spectroscopy analysis confirmed the formation of concentrated O^2-–vacancies in the co-doped ceria system. Impedance spectroscopy measurements revealed the high value of total ionic conductivity and low activation energy for the composition Ce_0.85La_0.075Dy_0.075O_2?δ i.e., 2.08 × 10^–2 S cm^–1 and 0.58 eV, respectively. Linear thermal expansion analyses of all the samples revealed the matched thermal expansion coefficients. Finally, these results recommend that the Ce_0.85La_0.075Dy_0.075O_2?δ sample can be useful as a solid electrolyte in IT-SOFC applications.