Thermal properties of perovskite RCeO 3 (R = Ba, Sr (original) (raw)
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Diffusion and Defect Data Pt.B: Solid State Phenomena, 2011
From neutron diffraction it is known that the BaCeO 3 perovskite undergoes a sequence of phase transformations from high temperature cubic C to rhombohedral R, to orthorhombic O1 (Imma) and to orthorhombic O2 (Pnma). Doping Y 3+ on the Ce 4+ site introduces charge compensating O vacancies (V O ) that may be partially filled with OH complexes with exposition to H 2 O, so making the material an ionic conductor.
Properties of Perovskite-Type Proton Conductors
2013
Investigations of perovskite-type BaCeO3 and SrCeO2 with various dopants (Y, Gd, Nd, and Ni) indicate that their microstructures and electrical properties are strongly influenced by the type and amount of dopants. Grain growth and densification of sintered samples are influenced by dopant level and A:B site nonstoichiometry. The conductivity of BaCe1_Y039 increases with the yttrium content in hydrogen and wet Ar; and exhibits a maximum in oxygen at an yttrium content of 10 to 20%. BaCe08Y0203_1 has the highest conductivity in a hydrogen atmosphere:-4.54 X 10-2 11' cm' at 600°C, and-4.16 >< 10 fl1 cm1 at 800°C. The effect of BaO excess depends on the concentration of dopant. Compared with BaCe091Y01503_0, doped BaCeO3 with BaO excess (Ba00.90Ce020.025Y203) has a higher total conductivity in all atmospheres studied (02, H2, and wet Ar), whereas the conductivity of BaCeO3 with excess BaO (Ba00.85Ce020.05Y203) is lower than that of BaCe09Y61O26. BaCeO3 based materials have higher conductivities than those of SrCeO2 based materials, whereas SrCeO3 based materials show higher proton transference numbers.
Computer Simulations of Thermal Expansion in Lanthanum-Based Perovskites
Journal of Solid State Chemistry, 2001
Di4erential thermal expansion is important when two strongly bonded ceramics are subjected to high temperatures, as in solid oxide fuel cells. Free energy minimization (EM) and molecular dynamics (MD) techniques were used to simulate the thermal expansion of the perovskites (La, Ca)CrO 3 and (La, Sr) (Co, Fe)O 3 on the atomistic scale. This paper explores the use of empirical partial charge interatomic potentials to represent the partially covalent bonding in these materials. The EM simulations underpredicted the thermal expansion coe7cients (CTEs) by up to 26% due to limitations in the potentials. The MD simulations predicted the CTEs to within 17% of experimental data for (La,Ca)CrO 3. MD predictions of the CTEs for (La,Sr)(Co,Fe)O 3 were signi5cantly lower than the experimental data due to the approximate nature of the Co 4؉ and Fe 4؉ interatomic potentials. Improvements in these results are possible if more extensive databases become available for re5ning the potentials and e4ective charges.
First principles calculations on the thermodynamic properties of PbTaO 3 and SnAlO 3 in a temperature range from 0 K to 800 K and pressure range from 0 GPa to 30 GPa have been carried out within the framework of density functional theory (DFT). The band structures of these oxides at different pressures display an increase in metallic character with a concomitant decrease in lattice constants, while the bulk modulus increases with increasing pressure. The thermal concert of these materials has been analyzed in terms of the temperature and pressure variation in Debye temperature, thermal expansion, entropy, and the Grü neisen parameter. Debye temperatures have been calculated from the elastic parameters as well as the quasi-harmonic Debye model, which are 339.07 GPa for PbTaO 3 and 714.36 GPa for SnAlO 3 .
Structural studies of the distorted perovskite proton conductors Sr 3Ca 1+ x Nb 2- x O 9- d
Solid State Ionics, 2002
The family of perovskites Sr 3 Ca 1 + x B 2 À x O 9 À d (B = Zr, Ta, Nb.. .) offer considerable potential as proton-conducting electrolytes that are relatively resistant to carbonation. In this study, we discuss the important structural features of these oxides and demonstrate that the structures of hydrated proton-conducting oxides differ quite significantly from those of unhydrated samples. Subtle changes in unit cell symmetry due to octahedral tilting/distortion, oxygen vacancy filling/creation and cation displacements are all important features accompanying water uptake/loss and play an intrinsic role in the level of proton conduction and mechanism of proton transfer.
Structural studies of the distorted perovskite proton conductors Sr 3 Ca 1+ x Nb 2− x O 9− δ
The family of perovskites Sr 3 Ca 1 + x B 2 À x O 9 À d (B = Zr, Ta, Nb.. .) offer considerable potential as proton-conducting electrolytes that are relatively resistant to carbonation. In this study, we discuss the important structural features of these oxides and demonstrate that the structures of hydrated proton-conducting oxides differ quite significantly from those of unhydrated samples. Subtle changes in unit cell symmetry due to octahedral tilting/distortion, oxygen vacancy filling/creation and cation displacements are all important features accompanying water uptake/loss and play an intrinsic role in the level of proton conduction and mechanism of proton transfer.
Journal of the European Ceramic Society, 2011
High-temperature proton conducting perovskite oxides have been fabricated by directional solidification using a laser-heated floating zone (LHFZ) method. Several families of compositions were selected: SrCe 1−x Y x O 3−δ (with x = 0.1, 0.2), BaCe 1−x M x O 3−δ (with M = Y, Yb and Ca; x = 0.05, 0.2), Sr 3 Ca 1.18 Nb 1.82 O 9−δ , SrZr 0.8 Y 0.2 O 3−δ and SrTi 0.95 Sc 0.05 O 3−δ. The resulting microstructures were characterized by electron microscopy and X-ray diffraction. The compounds exhibit a singular microstructure consisting of strongly textured crystalline cells surrounded by an intercellular amorphous phase. Compressive mechanical tests were performed at elevated temperatures in air at constant strain rate to evaluate the creep resistance. The results are discussed in terms of ionic radius, degree of aliovalence and content of dopant cations.
Solid State Ionics, 1999
The compounds BaCa Nb Nd O , SrCa Nb O with x 5 0.24 and Sr(Zr Ce) In O were 0.3 0.6 0.1 32d (11x) / 3 (22x) / 3 32x / 2 0.8 0.2 0.8 0.2 32d analyzed by thermogravimetry regarding their water uptake capacity. Solution enthalpies, entropies and maximum proton contents were extracted from the data. The compounds were also characterized by XRD. As expected, all compounds absorb water vapor and may be expected to show high-temperature proton conductivity. The first compound is derived from the complex perovskite BCN18 introduced by Nowick et al., the second one is the complex perovskite designated SCN24 by the same authors and the third is a new compound with partial substitution of Zr by Ce and trivalent doping.
Tritium conductivity and isotope effect in proton-conducting perovskites
Journal of the …, 1999
High temperature protonic-conducting oxides based on the perovskite structure have been studied extensively since their discovery in 1981. The hydrogen and deuterium isotope conductivities in these oxides have been evaluated 2,3 recently, and their potential application as hydrogen separation membranes has been discussed. However, there are no reported studies on the tritium ion-conduction in these perovskites. In this paper, we report the hydrogen (H), deuterium (D), and tritium (T) conductivities of three protonic conducting perovskites, viz. SrZr 0.9 Yb 0.1 O 2.95 , BaCe 0.9 Yb 0.1 O 2.95 , and SrCe 0.95 Yb 0.05 O 2.975 . The conductivity of tritium ions through these perovskites not only gives fundamental information regarding the hydrogen transport in these perovskites, but also allows for the exciting possibility of tritium separation using these oxides as an electrochemical membrane.
Powders of BaCe0.95Yb0.05O3-δ were synthesized using the standard solid-state reaction method. The produced materials were characterized by XRD, SEM, and Raman spectrometry. The absorption kinetics of hydrogen was studied using the TA-TQ500 TGA. The chemical and self-diffusion coefficients were computed, showing a three time increase of the diffusion coefficient from 1223 K to 1273. To explain these results we proposed the hypothesis that at high enough temperature the proton could have a high coordination number and could be interstitially located in tetrahedral and/or octahedral sites. Because, at high temperatures and during hydrogen absorption, there will be sufficient electrons in the conduction band to screen the proton and permit it to have a high coordination number and be interstitially located in the tetrahedral and octahedral sites. Then, there will be enough electrons in the conduction band to screen the proton. Moreover, The tested perovskite, during hydrogen diffusion at 1273 K, exhibited a cell expansion (Δa) of the cubic structure and consequently an increase in the cell volume. This cell expansion was the result of the inclusion of hydrogen in the perovskite framework, that produced the increment in the cell volume, merely by the existence of another constituent in the perovskite framework. At 1073 K and 1173 K, was not appreciated a variation of the unit cell parameters during hydrogen diffusion. We explain the cell expansion, during hydrogen chemical diffusion at 1273 K, as the result of the inclusion of hydrogen in the perovskite framework. This effect produced the cell volume increment, simply by the presence of an additional component included in the perovskite framework.