Data for: Optimisation of growth parameters to obtain epitaxial Y-doped BaZrO3 proton conducting thin films

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Structural transitions and conductivity of BaPrO3 and BaPr_0.9Y_0.1O_3-&#948

The temperature dependence of the crystal structures of the perovskites BaPrO3 and BaPr0.9Y0.1O3-d has been determined between room temperature and 900 \ub0C using time-of-flight neutron powder diffraction data. The orthorhombic room temperature structures evolve to a primitive cubic cell via three changes of symmetry Pnma -> Imma -> R-3c -> Pm-3m which occur at T~240, ~375, and ~860 \ub0C for BaPrO3. The stability fields of the Pnma and Pm-3m structures are lowered markedly by the presence of yttrium on the B-site. The first and last structural transitions are assigned as continuous events, and analysis of the octahedral tilt angle order parameter suggests the latter is tricritical in nature. The Imma -> R-3c transition is expected to be discontinuous first order and hysteresis effects in dilatometry data support this assignment although no discontinuity is found in the refined structural parameters. Conductivity data collected under dry, oxidising conditions reveal significantly higher conductivity levels in 10% acceptor (Y or Gd) substituted samples compared to undoped BaPrO3. For the acceptor substituted samples electron holes are the dominant charge carriers and the conductivity is weakly influenced by the changing crystal structure. In the undoped BaPrO3, a crossover, probably between extrinsic (impurity-derived) and intrinsic electronic conductivity, coincides with the high temperature rhombohedral to cubic transition

Influence of ZrO2 doping on microstructure and permeability of mesoporous TiO2 membrane

The influence of up to 30 mol% zirconia doping on microstructure, liquid permeability, thermal and chemical stability of mesoporous composite titania/zirconia membranes was investigated. It was demonstrated that zirconia retards the phase transformation of anatase until at least 700 °C. The pore size decreased gradually to 3.6 nm by addition of up to 20 mol% zirconia, while nitrogen sorption experiments showed that the porosity, BET surface area and pore connectivity increased. Chemical stability tests showed that undoped titania and composite titania/zirconia materials were stable in the pH range 1–13 at room temperature. The mechanical strength of titania membranes was significantly improved by addition of zirconia. The permeability of titania and titania/zirconia composite membranes was eight times larger than that of γ-alumina. The permeability was not affected by the level of zirconia doping or by the nature of the permeating liquid

Reduced long term electrical resistance in Ce/Co-coated ferritic stainless steel for solid oxide fuel cell metallic interconnects

The present study is focused on the influence of selected coatings on a ferritic stainless steel (Sanergy HT (TM), Sandvik) on the evolution of the area specific resistance (ASR) as a function of time at high temperature. The samples are exposed in humidified air at 850 degrees C for up to 4200 h. It combines long-term ASR measurements with the thermogravimetric behavior and microstructural analysis of the cross sections by scanning electron microscopy. The results show that uncoated and Co-coated Sanergy HT (TM) exhibit similar oxidation kinetics and comparable ASRs, while a combined Ce/Co coating improves oxidation resistance and, consequently, reduces the ASR significantly. Other reports have earlier shown that Co- (and Ce/Co)-coated Sanergy HT (TM) reduces the evaporation of volatile chromium species. Overall, the study indicates that Ce/Co-coatings will render substantially improved performance for ferritic steel interconnects for solid oxide fuel cells

Synthesis and electrical conductivity of gd-doped bapro3 powders

BaPrl-xGdxO3-d (GBP) was first discovered and proposed as potential proton conducting electrolyte in IT-SOFC in 1998. Its conductivity was reported to be the highest among all protonic conductors reported to date, even higher than doped BaCeO3. In the present work, GBP has been synthesized by using the acrylamide combustion method, which renders a final material with lower particle size, lower temperature sintering and better homogeneity than those obtained by the classical solid state method. Phase purity was achieved after a single thermal treatment of the precursor powder at 1000 °C during 5 hours. The material was characterized by X-ray diffraction, SEM, BET and thermogravimetric and thermodifferential analysis. SEM revealed the nanometric particles (∼ 150 nm) and BET confirmed partial sintering among them (2.85 m2/g; ∼320 nm). Sintering of bulk material is easily achieved using conventional uniaxial pressing. Stability tests under 5% H2/Ar and pure O2 are presented. The crystal structure remains unaltered under O2, but decomposition under H2 atmosphere occurs beyond 420°C. AC impedance spectroscopy has been also performed on dense samples in 5% H2/Ar and pure O2, both dry and wet, well below 420°C, the decomposition temperature in reducing conditions. It was noted that in all these measurements, the total conductivity is dominated by hole conduction. The different behaviour of the conductivity of the material under different conditions is discussed.</p

Synthesis and electrical conductivity of gd-doped bapro3 powders

BaPrl-xGdxO3-d (GBP) was first discovered and proposed as potential proton conducting electrolyte in IT-SOFC in 1998. Its conductivity was reported to be the highest among all protonic conductors reported to date, even higher than doped BaCeO3. In the present work, GBP has been synthesized by using the acrylamide combustion method, which renders a final material with lower particle size, lower temperature sintering and better homogeneity than those obtained by the classical solid state method. Phase purity was achieved after a single thermal treatment of the precursor powder at 1000 °C during 5 hours. The material was characterized by X-ray diffraction, SEM, BET and thermogravimetric and thermodifferential analysis. SEM revealed the nanometric particles (∼ 150 nm) and BET confirmed partial sintering among them (2.85 m2/g; ∼320 nm). Sintering of bulk material is easily achieved using conventional uniaxial pressing. Stability tests under 5% H2/Ar and pure O2 are presented. The crystal structure remains unaltered under O2, but decomposition under H2 atmosphere occurs beyond 420°C. AC impedance spectroscopy has been also performed on dense samples in 5% H2/Ar and pure O2, both dry and wet, well below 420°C, the decomposition temperature in reducing conditions. It was noted that in all these measurements, the total conductivity is dominated by hole conduction. The different behaviour of the conductivity of the material under different conditions is discussed.</p

In situ high temperature powder neutron diffraction study of undoped and Ca-doped La28-xW4+xO54+3x/2 (x=0.85)

In situ neutron diffraction experiments of 2% Ca-doped and nominally undoped lanthanum tungstate (La28-xW4+xO54+3x/2, with x = 0.85) have been carried out under controlled pD(2)O and pO(2) at elevated temperatures. All the diffraction patterns could be refined using an average cubic fluorite-related structure, in accordance with recent reports. The material exhibits disorder of the oxygen and the cation sublattices. Splitting of the oxygen sites around tungsten from the 32f to 96k Wyckoff position in the Fm (3) over barm space group improves the model and can better represent the oxygen disorder. No phase transition was detected from room temperature up to 800 degrees C under any of the studied conditions. Expansion of the unit cell constants in the presence of water at intermediate and low temperatures was correlated with the formation of protonic defects. The thermal expansion coefficient for lanthanum tungstate is rather linear under all studied conditions (similar to 11 x 10(-6) K-1). The in situ diffraction studies are correlated with dilatometry investigations and conductivity measurements

In situ high temperature powder neutron diffraction study of undoped and Ca-doped La28-xW4+xO54+3x/2 (x=0.85)

In situ neutron diffraction experiments of 2% Ca-doped and nominally undoped lanthanum tungstate (La28-xW4+xO54+3x/2, with x = 0.85) have been carried out under controlled pD(2)O and pO(2) at elevated temperatures. All the diffraction patterns could be refined using an average cubic fluorite-related structure, in accordance with recent reports. The material exhibits disorder of the oxygen and the cation sublattices. Splitting of the oxygen sites around tungsten from the 32f to 96k Wyckoff position in the Fm (3) over barm space group improves the model and can better represent the oxygen disorder. No phase transition was detected from room temperature up to 800 degrees C under any of the studied conditions. Expansion of the unit cell constants in the presence of water at intermediate and low temperatures was correlated with the formation of protonic defects. The thermal expansion coefficient for lanthanum tungstate is rather linear under all studied conditions (similar to 11 x 10(-6) K-1). The in situ diffraction studies are correlated with dilatometry investigations and conductivity measurements