Crystal structure and high-temperature electrical conductivity of novel perovskite-related gallium and indium oxides (original) (raw)
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The total electrical conductivity and the Seebeck coefficient of perovskite phases La 0.3 Sr 0.7 Fe 1Àx Ga x O 2.65+d (x ¼ 020:4) were determined as functions of oxygen nonstoichiometry in the temperature range 650-9501C at oxygen partial pressures varying from 10 À4 to 0.5 atm. Doping with gallium was found to decrease oxygen content, p-type electronic conduction and mobility of electron holes. The results on the oxygen nonstoichiometry and electrical properties clearly show that the role of gallium cations in the lattice is not passive, as it could be expected from the constant oxidation state of Ga 3+ . The nonstoichiometry dependencies of the partial molar enthalpy and entropy of oxygen in La 0.3 Sr 0.7 (Fe,Ga)O 2.65+d are indicative of local inhomogeneities, such as local lattice distortions or defect clusters, induced by gallium incorporation. Due to B-site cation disorder, this effect may be responsible for suppressing longrange ordering of oxygen vacancies and for enhanced stability of the perovskite phases at low oxygen pressures, confirmed by high-temperature X-ray diffraction and Seebeck coefficient data. The values of the electron-hole mobility in La 0.3 Sr 0.7 (Fe,Ga)O 2.65+d , which increases with temperature, suggest a small-polaron conduction mechanism. # 2002 Elsevier Science (USA)
Mixed oxide ion and electronic conductivity in perovskite-type SrSnO3 by Fe substitution
Materials Science and Engineering: B, 2003
The electrical conductivity properties of Fe-substituted SrSnO 3 perovskite-type oxides as a function of temperature and oxygen partial pressure are presented. SrSn 1(x Fe x O 3(d (05/x 5/1) was prepared by conventional solid state reaction in air using SrCO 3 , SnO 2 and FeC 2 O 4 ×/ 2H 2 O. The total electrical conductivity increases with increasing Fe content. Compounds containing low Fe contents (x B/0.5) are mixed oxide ion and electronic conductors in the oxygen partial pressure range between 10 (23 and 0.21 atm with predominant n-type and p-type electronic conduction at low and high oxygen partial pressure, respectively. SrSn 1(x Fe x O 3(d with high Fe-content (x !/0.5) is found to be a predominant electronic conductor over the entire oxygen partial pressure regime (10 (23 Á/0.21 atm). The average oxide ion transference number is found to be in the range 0.1 Á/0.5 at 600 Á/850 8C for x 0/0.1 Á/0.2. #
Inorganic Chemistry, 2017
Oxygen deficient Sr2ScGaO5 single-crystals with cubic perovskite structure were grown by the floating-zone technique. The transparent crystals of this pure 3D oxygen electrolyte are metastable at ambient temperature, showing 1/6 of all oxygen positions vacant. While neutron single crystal diffraction, followed by Maximum Entropy analysis, revealed a strong anharmonic displacements for the oxygen atoms, a predominant formation of ScO6 octahedra and GaO4 tetrahedra is indicated by Raman spectroscopic studies, resulting in a complex oxygen defect structure with short range order. Temperature dependent X-ray diffraction powder diffraction (XPD) and neutron powder diffraction (NPD) studies reveal the cubic Sr2ScGaO5 to be thermodynamically stable only above 1400°C, while the stable modification below this temperature shows the brownmillerite framework with orthorhombic symmetry. Cubic Sr2ScGaO5 remains surprisingly kinematically stable upon heating from ambient to 1300°C, indicating a huge inertia for the retransformation towards the thermodynamically stable brownmillerite phase. Ionic conductivity investigated by impedance spectroscopy was found to be 10-4 S/cm at 600°C, while oxygen 18 O/ 16 O isotope exchange indicates a free oxygen mobility to set in at around 500°C.
ECS Proceedings Volumes
The electrical conductivity properties of Ti-doped Lao.45Pro.45Sro.1Gao.8Mgo.2O2.85 (Pr-LSGM) and Fe-substituted SrSnO3 perovskite-type oxides as a function of temperature and oxygen partial pressure are presented. The oxides were prepared by solid-state reaction in air using stoichiometric amounts of metal oxides at elevated temperatures. The total electrical conductivity decreases with increasing Ti-content in Lao.45Pro.45Sro.1Gao.8-xTixMgo.2O2.85 and increases with increasing Fecontent in SrSni.xFexO3-8 Compounds containing low Fe contents (x < 0.5) are mixed oxide ion and electronic conductors in the oxygen partial pressure range between 10'23 and 0.21 atm with predominant n-type and ptype electronic conduction at low and high oxygen partial pressure, respectively. SrSni.xFexO3^ with high Fe-content (x > 0.5) is found to be a predominant electronic conductor over the entire oxygen partial pressure regime (IO 23-0.21 atm). The average oxide ion transference number for this range is found to be 0.1-0.5 at 5OO-8OO°C for x = 0.1 to 0.2.
Ionic and electronic conduction in stoichiometric and sub-stoichiometric perovskites
Solid State Ionics, 2000
A-site stoichiometric and sub-stoichiometric (La,Sr) (Ga,Cr)O perovskites, with y 5 0 or 0.05 and variable Cr 12y 32d content, were prepared by the ceramic route. Structural characterisation was carried out by X-ray diffraction (XRD). Electrical conductivity of samples was determined by impedance spectroscopy and dc measurements, as a function of temperature and oxygen partial pressure, in order to study the role of composition on the electrical properties. Cr content affects the activation energy of the electrical conductivity, and a transition from dominant ionic conduction to electronic conduction is observed. p-type conductivity is believed to dominate in air for materials with Cr content equal or higher than 20%. A-site sub-stoichiometry had no effect on improving the electrical properties.
Dalton transactions (Cambridge, England : 2003), 2014
Aliovalent substitution of Nb(5+) by Ti(4+) in Sr2LuNbO6 is limited to 10% of Nb atoms. A full structural determination by NPD confirms this and reveals that the structure is better described as a superstructure of the simple cubic perovskite (as previously reported) with the monoclinic cell 2(1/2)ap× 2(1/2)ap× 2ap and β≈ 90° (S.G. P21/n). The substituted materials present both oxygen-vacancies induced by charge compensation and Sr-deficiency. Therefore, their formula should be given as Sr2-yLuNb1-xTixO6-δ. Electrical properties can be fully understood considering these compositional defects. The parent compound Sr2LuNbO6 presents low electrical conductivity in air, which improves by more than one order of magnitude upon Ti substitution. In any case, the title oxides show low electrical conductivity in a wide oxygen partial pressure (pO2) range (10(-25) atm ≤pO2≤ 10(-1) atm). At high pO2 the conductivity increases with pO2 due to oxygen-vacancy annihilation and hole creation, accord...
Mixed conductivity and stability of A-site-deficient Sr(Fe,Ti)O 3–δ perovskites
Journal of Solid State Electrochemistry, 2002
Deficiency in the A sublattice of perovskite-type Sr1–y Fe0.8Ti0.2O3–δ (y=0–0.06) leads to suppression of oxygen-vacancy ordering and to increasing oxygen ionic conductivity, unit cell volume, thermal expansion, and stability in CO2-containing atmospheres. The total electrical conductivity, predominantly p-type electronic in air, decreases with increasing A-site deficiency at 300–700 K and is essentially independent of the cation vacancy concentration at higher temperatures. Oxygen ion transference numbers for Sr1–y Fe0.8Ti0.2O3–δ in air, estimated from the faradaic efficiency and oxygen permeation data, vary in the range from 0.002 to 0.015 at 1073–1223 K, increasing with temperature. The maximum ionic conductivity was observed for Sr0.97Fe0.8Ti0.2O3–δ ceramics. In the system Sr0.97Fe1–x Tix O3–δ (x=0.1–0.6), thermal expansion and electron-hole conductivity both decrease with x. Moderate additions of titanium (up to 20%) in Sr0.97(Fe,Ti)O3–δ result in higher ionic conductivity and lower activation energy for ionic transport, owing to disordering in the oxygen sublattice; further doping decreases the ionic conduction. It was shown that time degradation of the oxygen permeability, characteristic of Sr(Fe,Ti)O3–δ membranes and resulting from partial ordering processes, can be reduced by cycling of the oxygen pressure at the membrane permeate side. Thermal expansion coefficients of Sr1–y Ti1–x Fex O3–δ (x=0.10–0.60, y=0–0.06) in air are in the range (11.7–16.5)×10–6 K–1 at 350–750 K and (16.6–31.1)×10–6 K–1 at 750–1050 K.
Mixed conductivity and stability of A-site-deficient Sr(Fe,Ti)O 3-δ perovskites
Journal of Solid State Electrochemistry, 2002
Deficiency in the A sublattice of perovskitetype Sr 1-y Fe 0.8 Ti 0.2 O 3-d (y=0-0.06) leads to suppression of oxygen-vacancy ordering and to increasing oxygen ionic conductivity, unit cell volume, thermal expansion, and stability in CO 2 -containing atmospheres. The total electrical conductivity, predominantly p-type electronic in air, decreases with increasing A-site deficiency at 300-700 K and is essentially independent of the cation vacancy concentration at higher temperatures. Oxygen ion transference numbers for Sr 1-y Fe 0.8 Ti 0.2 O 3-d in air, estimated from the faradaic efficiency and oxygen permeation data, vary in the range from 0.002 to 0.015 at 1073-1223 K, increasing with temperature. The maximum ionic conductivity was observed for Sr 0.97 Fe 0.8-Ti 0.2 O 3-d ceramics. In the system Sr 0.97 Fe 1-x Ti x O 3-d (x=0.1-0.6), thermal expansion and electron-hole conductivity both decrease with x. Moderate additions of titanium (up to 20%) in Sr 0.97 (Fe,Ti)O 3-d result in higher ionic conductivity and lower activation energy for ionic transport, owing to disordering in the oxygen sublattice; further doping decreases the ionic conduction. It was shown that time degradation of the oxygen permeability, characteristic of Sr(Fe,Ti)O 3-d membranes and resulting from partial ordering processes, can be reduced by cycling of the oxygen pressure at the membrane permeate side. Thermal expansion coefficients of Sr 1-y Ti 1-x Fe x O 3-d (x=0.10-0.60, y=0-0.06) in air are in the range (11.7-16.5)·10 -6 K -1 at 350-750 K and (16.6-31.1)·10 -6 K -1 at 750-1050 K.