La0.8Sr0.2Ga0.8Mg0.2O3-δ Research Articles

A limiting current oxygen sensor with La0.8Sr0.2(Ga0.8Mg0.2)1-x Fe x O3-δ dense diffusion barrier

La0.8Sr0.2(Ga0.8Mg0.2)1-x Fe x O3-δ (LSGMF, x = 0.2–0.9) was prepared by a solid-state reaction method, and the characterization was investigated. Limiting current oxygen sensors were fabricated with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) as solid electrolyte and La0.8Sr0.2(Ga0.8Mg0.2)0.1Fe0.9O3-δ (LSGMF9) as dense diffusion barrier. The influences of temperature, oxygen concentration, and the thickness of dense diffusion barrier (L) on sensing properties of oxygen sensors were investigated. The results show that the crystal structure of samples is perovskite. The electrical conductivity increases with increasing x. A transition from semiconductive to pseudometallic behavior which is associated with oxygen losses from the lattice is observed with an increase of temperature for x = 0.3, 0.5, and 0.7. The thermal expansion coefficient (TEC) in the temperature range 300–1000 °C increases to a maximum and then decreases with increasing x. TECs between LSGMF9 and LSGM are close. The limiting current oxygen sensor exhibits an excellent sensing performance, and the limiting current responses depend linearly on the oxygen concentration. As the L value increases, the limiting current decreases. The polarization resistance of the sensor decreases with increasing oxygen concentration.

Enhanced sintering of Ce0.8Nd0.2O2−δ-La0.8Sr0.2Ga0.8Mg0.2O3−δ using CoO as a sintering aid

Ce0.8Nd0.2O1.9 (NDC) and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolytes were prepared using a sol-gel method. NDC-LSGM composite electrolytes were subsequently prepared by adding 5% (w, mass fraction) precalcined LSGM powders to NDC sols. The electrolyte materials of NDC-Co and NDC-LSGM-Co were obtained by adding 1mol% CoO to NDC sols and NDC-LSGM composite electrolytes, respectively. The microstructure and phase composition of the pellets were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS). The electrical conductivities of the pellets were measured using alternative current (AC) impedance spectroscopy. The results indicate that a single perovskite phase is observed for the LSGM ceramic, while NDC-Co, NDC-LSGM and NDC-LSGM-Co have a cubic fluorite structure similar to that of NDC. As a sintering aid, CoO can further promote grain growth and increase relative density (＞95%) of the NDC-LSGM composite electrolyte. The enhancement of the total conductivity is primarily attributed to the large increase in the conductivity of the grain boundary. However, the slight decrease of the grain boundary conductivity of the NDC-LSGM-Co electrolyte is caused by the presence of trace amounts of impurity phases in the grain boundaries.

Electrochemical Performance of La1.5Sr0.5Ni1-xFexO4+δ Cathode for IT-SOFCs

La1.5Sr0.5Ni1-xFexO4+δ (LSNF, x=0, 0.3, 0.5) series materials are synthesized as potential cathode materials for intermediate-temperature solid fuel cells by an EDTA-citrate complexation process. The effects of Fe substitution for Ni on the structure, transport property and electrochemical performances are investigated. X-ray diffraction shows that all samples with Fe-doping are identified as single phase materials with a tetragonal I4/mmm space group. Fe-doping decreases electrical conductivity of La1.5Sr0.5Ni1-xFexO4+δ. The study of symmetrical cells with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) as an electrolyte shows a decreasing tendency of polarization resistance (Rp) of La1.5Sr0.5Ni1-xFexO4+δ with increasing Fe content. The impedance data at different oxygen partial pressures reveal that the electrode reaction is controlled by the molecular oxygen dissociation and charge transfer processes. The substitution of Fe improves the electrode kinetics and enhances the electrochemical performance of LSNF electrode significantly. The LSGM electrolyte (400μm) supported single cell with La1.5Sr0.5Ni0.5Fe0.5O4+δ as cathode and Ni-Gd0.1Ce0.9O2-δ as anode delivers relatively high power density of 282mWcm−2 at 800°C.

Superior electrochemical performance of non-precious Co-Ni-Mo alloy catalyst-impregnated Sr2FeMoO6-δ as an electrode material for symmetric solid oxide fuel cells

Double perovskite-based Sr2FeMoO6-δ (SFM), as an electrode material for symmetric solid oxide fuel cells (SOFCs), has been synthesized by a sucrose-modified combustion technique. SFM showed metallic conducting behavior with a conductivity of 215.72Scm−1 in dry H2 at 800°C. The polarization resistance (Rp) for H2 oxidation, evaluated using half-cell symmetry, was recorded as 0.192Ωcm2 under humidified H2 at 800°C. Improved catalytic activity was accomplished by impregnation of Pd or Co-Ni-Mo (0.1:5:1 molar ratio, CNM) via a glycine-mediated impregnation technique. The Rp values for the Pd- and CNM-impregnated SFM were 0.087 and 0.060Ωcm2, respectively, under humidified H2 at 800°C. The symmetric SOFC with an La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte and a CNM-impregnated SFM electrode showed maximum power densities of 1066mWcm−2 and 480mWcm−2 at 800°C under humidified H2 and CH4, respectively.

Copper-doped lanthanum ferrites for symmetric SOFCs

Structure stability and electrical conductivity of La1-xSrxFe0.8Cu0.2O3-δ with x = 0.2, 0.4 were investigated both in air and in hydrogen to explore their potential applications as symmetric electrodes for solid oxide fuel cells. La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte supported symmetric fuel cells were fabricated and tested in air/hydrogen ambient in 650–800 °C temperature range achieving a maximum power density of 162 mW cm−2. To improve the cell performance, a composite electrode (70 wt% La1-xSrxFe0.8Cu0.2O3-δ −30 wt% Gd0.2Ce0.8O3-δ) was successfully evaluated both at the anode and the cathode sides decreasing the cell polarization resistance to 0.454 Ω cm2 at 800 °C and reaching a single cell maximum power density of 294 mW cm−2.

Flash-Sintering and Characterization of La0.8Sr0.2Ga0.8Mg0.2O3-δ Electrolytes for Solid Oxide Fuel Cells

La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM), a promising electrolyte material for intermediate temperature solid oxide fuel cells, can be sintered to a fully dense state by a flash-sintering technique. In this work, LSGM is sintered by the current-limiting flash-sintering process at 690°C under an electric field of 100Vcm−1, in comparison with up to 1400°C or even higher temperature in conventional furnace sintering. The resultant LSGM samples are investigated by scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy. The SEM images exhibit well-densified microstructures while XRD results show that the perovskite structure after flash-sintering does not changed. EIS results show that the conductivity of LSGM sintered by the current-limiting flash-sintering process increases with sintering current density value. The conductivity of samples sintered at 120mAmm−2 reaches 0.049σcm−1at 800°C, which is approximate to the value of conventional sintered LSGM samples at 1400°C. Additionally, the flash-sintering process is interpreted by Joule heating theory. Therefore, the current-limiting flash-sintering technique is proved to be an energy-efficient and eligible approach for the densification of LSGM and other materials requiring high sintering temperature.

Evaluation of MIEC Ce0.8Y0.1Mn0.1O2-δ Anode in Electrolyte-Supported SOFC

In this study, the electrochemical performance of a single phase, mixed ion and electron conducting (MIEC) Ce0.8Y0.1Mn0.1O2-δ (10CYMO) anode was evaluated using symmetrical half-cell and full-cell configurations under humidified H2, 10 ppm H2S/H2, and CH4. An yttria-stabilized zirconia (YSZ) electrolyte support layer was used in this work, as ac impedance spectroscopy revealed that the 10CYMO/YSZ/10CYMO cell gave the lowest area specific polarization resistance (ASR) of 0.23 Ωcm2 at 800°C in wet H2, compared to La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) and Zr0.89Sc0.1Ce0.01O2-δ (ScSZ). Exposure of the 10CYMO anodes to 10 ppm H2S/H2, either in a half-cell or full cell configuration, showed slight enhancement on the electrochemical performance, which was explained using a concept describing the sulfur and ceria interaction. The performance of a 10CYMO/YSZ/La0.8Sr0.2MnO3-δ _ YSZ full cell was evaluated under 90%H2-N2/3%H2O, giving a power density of 75 mW/cm2 at 800°C and is better than seen for other fluorite-based anodes reported in the literature.

Substrate Temperature and La<sub>0.9</sub>Sr<sub>0.1</sub>Ga<sub>0.8</sub>Mg<sub>0.2</sub>O<sub>3-δ</sub> Electrolyte Film Growth by Radio Frequency Magnetron Sputtering

La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte thin films were fabricated on La0.7Sr0.3Cr0.5Mn0.5O2.75 (LSCM) porous anode substrates by Radio Frequency (RF) magnetron sputtering method. The compatibility between LSGM and LSCM was examined. Microstructures of LSGM thin films fabricated were observed by scanning electron microscope (SEM). The effect of substrate temperature on LSGM thin films was clarified by X-ray Diffraction (XRD). Deposition rate increases firstly at the range of 50°C~150°C, and then decreases at the range of 150°C ~300°C. After annealing, perovskite structure with the same growth orientation forms at different substrate temperature. Crystallite size decreases at first, to the minimum point at 150°C, then increases as substrate temperature rises.

Shape-Dependent Activity of Ceria for Hydrogen Electro-Oxidation in Reduced-Temperature Solid Oxide Fuel Cells.

Single crystalline ceria nanooctahedra, nanocubes, and nanorods are hydrothermally synthesized, colloidally impregnated into the porous La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) scaffolds, and electrochemically evaluated as the anode catalysts for reduced temperature solid oxide fuel cells (SOFCs). Well-defined surface terminations are confirmed by the high-resolution transmission electron microscopy--(111) for nanooctahedra, (100) for nanocubes, and both (110) and (100) for nanorods. Temperature-programmed reduction in H2 shows the highest reducibility for nanorods, followed sequentially by nanocubes and nanooctahedra. Measurements of the anode polarization resistances and the fuel cell power densities reveal different orders of activity of ceria nanocrystals at high and low temperatures for hydrogen electro-oxidation, i.e., nanorods > nanocubes > nanooctahedra at T ≤ 450 °C and nanooctahedra > nanorods > nanocubes at T ≥ 500 °C. Such shape-dependent activities of these ceria nanocrystals have been correlated to their difference in the local structure distortions and thus in the reducibility. These findings will open up a new strategy for design of advanced catalysts for reduced-temperature SOFCs by elaborately engineering the shape of nanocrystals and thus selectively exposing the crystal facets.

LSGM-based Cells for IT-SOFC Applications

Solid Oxide Fuel Cells have still many technical problems related to its high operating temperature (800–1000 °C). The most recent studies deal with reducing the operation temperature increasing at the same time the durability of the device. The use of La0.8Sr0.2Ga0.8Mg0.2O3-δ(LSGM) perovskite as electrolyte, could be a very promising solution for IT-SOFC operating at 600°C. In this work, LSGM bilayers constituted by a thicker porous layer (namely the anode scaffold) and a dense electrolyte were produce by co-firing using two different techniques: i) die-pressing + spin coating, ii) tape casting + lamination. In both cases the nature and amount of pore former needed to obtained an anode scaffold with a porous network suitable for the Ni impregnation process were deeply investigated. In the die-pressing + spin coating method, supporting anodes were prepared pressing LSGM commercial powder with a proper amount of binder and a tailored mixture of pore forming agents. Onto the pre-sintered anode support, an electrolyte layer was deposited by spin coating. In the tape casting + lamination route, the starting ceramic suspensions with and without pore formers were carefully optimized to produce the anodic and electrolytic green tape respectively, while the lamination parameters, in terms of temperature, time and pressure, were adjusted to obtain defect-free bilayers. The sintering conditions were also optimized in order to achieve the best compromise in terms of density of the electrolyte and porosity of the anode scaffold. Structural and morphological characterizations of the produced bilayers as well as the electrochemical performances of the cells in the temperature range 600-750°C will be reported. The potentialities and disadvantages of the two processing approaches will be thoroughly discussed.

LSGM-based Cells for IT-SOFC Applications

Solid Oxide Fuel Cells have still many technical problems related to its high operating temperature (800–1000 °C). The most recent studies deal with reducing the operation temperature increasing at the same time the durability of the device. The use of La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) perovskite as electrolyte, could be a very promising solution for IT-SOFC operating at 600°C. In this work, LSGM bilayers constituted by a thicker porous layer (namely the anode scaffold) and a dense electrolyte were produced by tape casting. The critical issues to obtain flexible and crack-free green tapes suitable for lamination were carefully examined. In particular, the nature and amount of pore former needed to obtain an anode scaffold with a porous network suitable for the catalysts impregnation process were deeply investigated.

Influence of Substrate on Conductivity of Sr and Mg Doped Lanthanum Gallate Thin Film Electrolyte for Solid Oxide Fuel Cell

In order to reveal the influence of substrate on the conductivity change of La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) thin film from the bulk, we prepared LSGM thin films on the sapphire and the quartz substrates by radio frequency magnetron sputtering, and evaluated the crystallinity, the microstructure, and the conductivity. The lattice constant of 0.6 μm thick film was different between the substrates. Compared with the bulk, the lattice constant of the thin film on the sapphire substrate was decreased 1.3%, and that on the quartz substrate was increased 0.7%. The grains in the thin film on the quartz substrate were approximately 0.2 μm in size, and those on the sapphire substrate were approximately 0.1 μm in size. The conductivity was measured at 710 °C by electrochemical impedance spectroscopy. The conductivity of the thin film on the quartz substrate was σ = 2.2 × 10-3 Scm-1 and that on the sapphire substrate was 9.0 × 10-4 Scm-1. The reason why the thin film on the quartz substrate had higher ion conductivity than that on the sapphire substrate can be attributed to the higher density of the grain boundaries which govern the total resistivity of the film on the quartz substrate than that on the sapphire substrate.

Grain Size Effect on Conductivity of LSGM Thin Film Electrolyte for Solid Oxide Fuel Cell

The grain size effect of La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte thin film was investigated in order to clarify the mechanism of the change of ion conductivity of thin film. The film was deposited on a LaSrGaO4 (LSGO) substrate by radio frequency magnetron sputtering and then annealed at 900 oC or 1100 oC to change the grain size in the film. The mean grain size in the films annealed at 900 oC and 1100 oC was 80 nm and 281 nm, respectively. The ion conductivity was measured by electrochemical impedance spectroscopy (EIS). The ion conductivity values of the film of the mean grain size of 80 and 281 nm at 800oC were σ=1.34×10-2 and 1.81×10-2 S/cm, respectively. The activation energy value of both films was 1.08 eV. The grain boundary conductivity obtained by applying the Brick-layer model was nearly two orders of magnitude lower than the bulk conductivity. The activation energy value of the grain boundary conductivity was 1.33 eV. The resistance to transport the ions across the grain boundary should be high. The higher conductivity of the 1100 oC annealed film derives from the decrease of the high resistive grain boundary density.

Li/Na Modified Ni-SDC Anode for Methane-Fueled Solid Oxide Fuel Cells

A facile chemically lithium/sodium insertion method has been developed to prepare Li/Na modified-NiO composites (Li/Na-NiO). The single cells were fabricated with a Li/Na modified NiO-Ce0.8Sm0.2O1.9 (SDC) composite anode screened on a 300µm La0.9Sr0.1Ga0.8Mg0.2O3-δ(LSGM) electrolyte and a composite cathode consisting of Sr0.95Ce0.05CoO3-δ and SDC (30wt%). The cells with Li/Na modified Ni-SDC anode material deliver much higher open circuit voltages (OCV) than that of the cell with pure Ni-SDC anode. When wet CH4 was used as fuel, the peak power densities of the cells with the Li and Na modified Ni-SDC anode reach about 212mW cm-2 and 231mW cm-2 at 800oC, respectively, which were much higher than that with the pristine Ni-SDC anode. In addition, the cells with Li/Na modified Ni-SDC anode materials show better long-term stability at 800oC. The preliminary results demonstrate that the Li/Na modified Ni-SDC anode materials are promising alternative anode for hydrocarbon-fueled solid oxide fuel cells.

Kinetic Study of La0.75Sr0.25Cr0.5Mn0.5O3-Δ Nanoelectrodes for Symmetrical-SOFC

One of the main technological challenges of the solid oxide fuel cells (SOFC) is to reduce its operating temperature. Nanostructured materials open this possibility since the microstructure plays a fundamental role on the electrocatalytic activity of the electrodes. In this context, the understanding of the limiting mechanism steps for both O2 reduction and H2 oxidation reactions is a main objective in order to improve the design of the nanostructured electrodes. La0.75Sr0.25Cr0.5Mn0.5O3- δ (LSCM) perovskite has demonstrated a promising combination of properties for its employ as electrode (anode and cathode, simultaneously) in symmetrical-SOFC, among which it can mention: phase and dimensional stability, high electrochemical activity in both reducing and oxidizing atmospheres, and chemical compatibility with various solid electrolytes. In recent works, we present the synthesis by combustion of pure-phase LSCM nanocrystallites [1], and the bottom-up building process of nanostructured LSCM electrodes employing La0.8Sr0.2Ga0.8Mg0.2O3-δ(LSGM) as electrolyte [2]. In particular, the influence of the electrode crystallite size on the electrochemistry behavior as both anode and cathode was studied by electrochemical impedance spectroscopy (EIS). In this work, we present an electrode kinetics study of the nanostructured LSCM material by employing EIS measurements in different oxidizing and reducing atmospheres. Figures (a) and (b) present the EIS spectra of LSCM/LSGM/LSCM cell varying the oxygen and hydrogen partial pressures, i.e. pO2 and pH2 respectively. As it can be observed, when both pO2 and pH2 increase the electrode polarization resistance decrease, which indicates that the LSCM nanocrystallites are electrocatalytically active both for the oxygen reduction as well as hydrogen oxidation. Figures (c) and (d) show the evolution of the polarization resistance with the pO2 and pH2 obtained by fitting of the EIS spectra by using Electrical Equivalent Circuits. In both cases, two EIS arcs at high and low frequency (HF and LF, respectively) can be resolved showing complex mechanisms. In the H2 oxidation, the HF contribution with n ≈ 0 is independent of H2 concentration, probably due to a charge transfer process, while the LF contribution with n ≈ 0.5 could involve atomic species, e.g. H2-dissociative adsorption or H-surface diffusion [3]. On the other hand, in the O2 reduction, the HF contribution with n ≈ 0.25 is typically assigned to O-surface transport process whereas the LF arc with n ≈ 1 is generally attributed to O2 mass transfer in the gas phase [4].

Study of Electrode Performance for Nanosized La0.4Sr0.6Co0.8Fe0.2O3-Δ IT-SOFC Cathode

La0.4Sr0.6Co0.8Fe0.2O3-δ (LSCF4682) perovskites were successfully synthesized by an assisted ammonium nitrate combustion method. The sample shows a sponge-like structure with meso and macro-pores channels distributed between interconnected nanosized particles (~45 nm) with a high specific surface area. Cathode performance of LSCF4682 was investigated in the intermediate temperature range of 400°C-700°C by using symmetrical cell configuration on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. The cathode polarization resistances Rc,p are 0.067 and 0.035 Ω·cm2 at 600°C and 700 °C, respectively. The long-term behavior of Rc,p was studied by applying an accelerate aging at 800 °C and testing the polarization resistance at 700°C as a function of time. After 500 h of aging, a degradation rate of (1/RC,P)(dRC,P/dt)= 0.002 h-1 raises the Rc,p to 0.1 Ω·cm2 at 700°C. A maximum power density of 1.23 Wcm-2 was achieved at 650 °C testing the LSCF cathode deposited on a porous SLT-LSGM supported multilayer cell. The results demonstrate that this material is a competitive SOFC cathodes for the intermediate temperature operation.

Solid oxide fuel cells with (La,Sr)(Ga,Mg)O3-δ electrolyte film deposited by radio-frequency magnetron sputtering

In this study, solid oxide fuel cells (SOFCs) containing a high quality La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) film deposited on anode supported substrate using RF magnetron sputtering are successfully prepared. The anode substrate is composed of two functional NiO/Sm0.2Ce0.8O2-δ (SDC) composite layers with ratios of 60/40 wt% and 50/50 wt% and a current collector layer of pure NiO. The as-deposited LSGM film appears to be amorphous in nature. After post-annealing at 1000 °C, a uniform and dense polycrystalline film with a composition of La0.87Sr0.13Ga0.85Mg0.15O3-δ and a thickness of 3.8 μm is obtained, which was well adhered to the anode substrate. A composite LSGM/La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) layer, with a ratio of 30/70 wt%, is used as the cathode. The SOFC prepared reveals a good mechanical integrity with no sign of cracking, delamination, or discontinuity among the interfaces. The total cell resistance of a single cell with LSGM electrolyte film declines from 0.60 to 0.10 Ω cm2 as the temperature escalates from 600 to 800 °C and the open circuit voltage (OCV) ranges from 0.85 to 0.95 V. The maximum power density (MPD) of the single cell is reported as 0.65, 1.02, 1.30, 1.42, and 1.38 W cm−2 at 600, 650, 700, 750, and 800 °C, respectively. The good cell performance leads to the conclusion that RF magnetron sputtering is a feasible deposition method for preparing good quality LSGM films in SOFCs.

Symmetric electrodes for solid oxide fuel cells based on Zr-doped SrFeO3−δ

SrFe1−xZrxO3−δ (0 ≤ x ≤ 0.35) compounds have been investigated as potential symmetric electrode materials for solid oxide fuel cells (SOFCs). The crystal structure changes from orthorhombic to cubic perovskite when iron is partially replaced by Zr4+. The compounds with Zr-content x ≥ 0.1 are structurally stable under reducing atmospheres up to 800 °C. The oxygen nonstoichiometry and thermal expansion coefficients of the compounds are determined by thermogravimetric analysis and high temperature X-ray diffraction respectively, and both decrease with increasing Zr-content, indicating that Zr4+ improves the redox stability of SrFeO3−δ. Total conductivity and area specific resistance (ASR) are determined in air and 5% H2–Ar. SrFe0.75Zr0.25O3-δ exhibits ASR values as low as 0.1 and 0.17 Ω scm2 in air and 5% H2–Ar at 750 °C respectively. The performance of these compounds as both cathode and anode materials is tested in a single cell with 400 μm-thick La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte, reaching a maximum power density of 425 mW cm−2 at 800 °C.

The Preparation of Pervoskite Oxide Powders Adopted in ITSOFC via Inductively Coupled Plasma Technique

The Sm0.5Sr0.5CoO3-δ (SSC), La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) perovskite oxide powders commonly used as electrode and/or electrolyte materials of intermediate temperature solid oxide fuel cells (ITSOFCs) are successfully synthesized by inductively coupled plasma (ICP) synthesis technique in this study. These powders synthesized from the well chelating precursor solutions at the torch powers from 16.2 to 22.2 kW and calcined at the temperatures from 900 to 1400℃ are in a highly pure phase. The XRD results of these calcined powders indicate the S/P ratios (the ratio of the mostly intense diffraction intensity of secondary phase to that of primary phase) are all less than 3%. The morphology and particle sizes of synthesized oxide powders were observed by electron microscopy. The results show that the primary particle sizes of as-synthesied powders are all about 5-50 nm.

Electrochemical Characterization of La0.9Sr0.1Ga0.8Mg0.2O3-δ Thin Film Electrolyte Deposited by Radio Frequency Magnetron Sputtering

To reveal the mechanism of the conductivity change of La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) thin film from the bulk, the LSGM thin films with different thickness deposited on sapphire substrate by radio frequency magnetron sputtering was studied. The grains in thick (1.8 μm~) film had a nearly sphere shape and approximately 0.3 μm in size. The grains in thin (~0.6 μm) film had a nearly spatulate and approximately 0.1 μm in size. The lattice constant of the 0.6 μm thickness film was decreased from that of the bulk by the influence of the substrate. The conductivity values in 3.0 and 0.6 μm thickness film at 700 oC were 2.3×10-3 and 1.1×10-3 Scm-1, respectively. Their activation energy were 1.07 and 1.26 eV, respectively. The thicker the film is, the conductivity increases and the activation energy decreases. This should be caused by the smaller bulk resistivity than the grain boundary resistivity.