Nina Orlovskaya

Ferroelasticity in mixed conducting LaCoO3 based perovskites: a ferroelastic phase transition

Abstract The defect structure of LaCoO 3 based ferroic perovskites has been studied by TEM. The dynamics of the temperature-induced ferroelastic to paraelastic phase transition was directly monitored by in-situ TEM during thermal cycles from room temperature to 700 °C. Different types of structural features of LaCoO 3 based perovskites have been observed, such as twins, antiphase domains, stacking faults, and dislocations. Domain motion and de-twinning during heating, and the reappearance of twins during cooling have been demonstrated. This is important for the understanding of ferroelastic hysteretic behavior of LaCoO 3 based perovskite ceramics.

Mechanical properties of LaCoO3 based ceramics

Abstract Mechanical characteristics of LaCoO 3 based ceramics have been measured over the temperature range from room temperature (RT) to 850°C. The bending strength is in the range of 53 MPa for 83% dense LaCoO 3 , 76 MPa for 90% dense La 0.8 Sr 0.2 CoO 3 , and 150 MPa for 99% dense La 0.8 Ca 0.2 CoO 3 ceramics at RT. The strength of LaCoO 3 and La 0.8 Sr 0.2 CoO 3 was relatively independent of temperature up to 850°C. The strength of the dense La 0.8 Ca 0.2 CoO 3 material decreased linearly to 850°C, where the strength at 850°C is only about 50% of the strength at RT. The fracture mode of this material is changed from fully transgranular at RT to mixed trans- and intergranular at 850°C. Hardness in the range of 7–9 GPa for 90% dense La 0.8 Sr 0.2 CoO 3 and 9–11 GPa for fully dense La 0.8 Ca 0.2 CoO 3 ceramics have been observed. The fracture toughness is calculated to be 0.73±0.08 MPa m 1/2 for 90% dense La 0.8 Sr 0.2 CoO 3 , and 0.98±0.09 MPa m 1/2 for fully dense La 0.8 Ca 0.2 CoO 3 ceramics. Youngs modulus for dense La 0.8 Ca 0.2 CoO 3 was measured to be 112±3 GPa.

Ferroelasticity and hysteresis in LaCoO3 based perovskites

Perovskite-type ABO3 (where A La, Ca; B Co) ceramics are very promising materials for oxygen separation membrane and solid oxide fuel cells applications. However, their mechanical behavior has not yet been adequately studied. We studied the mechanical performance of perovskite ceramics using a combination of microindentation, compression, and bending. Our work demonstrated ferroelastic hysteretic behavior during indentation and compression loading in LaCoO3 based perovskites. This behavior can be caused by domain reorientation and/or phase transformation. Domain switching under the compression loading in LaCoO3 based perovskites has been demonstrated by XRD. Nonlinearity during fracture toughness measurements was observed in the dense La0.8Ca0.2CoO3 perovskite. Such nonlinearity can be assigned to the domain switching or the phase transformation during crack propagation. This might be a reason of a higher fracture toughness of this material compared to non-ferroelastic composition.  2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Mixed ionic electronic conducting perovskites for advanced energy systems

Contributing Authors. Preface. Acknowledgements. Oxide Components for the Solid Oxide Fuel Cell J.B. Goodenough. Vacancy Segregation at Grain Boundaries in Ceramic Oxides N.D. Browning, et al. Metallic Conductivity and Magnetism: The Great Potential of Manganese and Cobalt Perovskites B. Raveau. Raman Diagnostics of LaCoO3 Based Properties N. Orlovskaya, D. Steinmetz. Mobility and Reactivity of the Surface and Lattice Oxygen of Some Complex Oxides with Perovskite Structure V.A. Sadykov, et al. LaFeO3 and LaCoO3 Based Perovskites: Preparation and Properties of Dense Oxygen Permeable Membranes K. Wiik, et al. Optimisation of Perovskite Materials for Fuel Electrodes S.W. Tao, J.T.S. Irvine. Single Crystal Growth of Oxides and Refractory Materials G. Balakrishnan, et al. Ionic Transport in Perovskite-Related Mixed Conductors: Ferrite-, Cobaltite-, Nickelate- and Gallate-Based Systems A. Kovalevsky, et al. Structural/Property Relationships of the Mixed Electronic/Ionic Conductors Based on Lanthanum Gallate N. Sammes. Microwave-Assisted Regeneration of Soot Filters Y. Zhang-Steenwinkel, et al. Microheterogeneous Solid Solutions in Perovskites: Formation, Microstructure and Catalytic Activity L.A. Isupova, et al. Phase Transitions and Ion Transport in SrFe1-xMx)2.5, Where M = Ga, Cr M.V. Patrakeev, et al. Connection of Giant Volume Magnetostriction with Colossal Magnetoresistance in Manganites L.I. Koroleva. SOFC Perspectives in Ukraine O.D. Vasylyev. Measurement of Oxygen Ionic Transport in Mixed Conductors E. Naumovich, et al. A New Approach to the Defect Chemistry of Doped La1-DeltaMnO3+delta K. Nakamura. Structure, Microstructure and Transport Properties of Mixed Conducting Lanthanum Gallate Based Perovskite Ceramics E.D. Politova, et al. Synthesis Structure Peculiarities of (La, Sr)MnO3 Based Nanomanganites I. Danilenko, et al. Nanoscale Magnetism and Magnetotransport Phenomena of (LaSr)MnO Compact V. Krivoruchko, et al. LSGM Single Crystals: Crystal Structure, Thermal Expansion, Phase Transitions and Conductivity L. Vasylechko, et al. Real Structure of LSGMO Crystal Studied by Laue Method D. Savytskii, et al. Microwave Regeneration of Diesel Soot Filters L.M. van der Zande, et al. Oxygen Transport in Composite Materials for Oxygen Separators and Syngas Membranes M. Dhallu, et al. Pulsed Lased Deposition of MIEC Sr4Fe6O13+-d Epitaxial Thin Films J.A. Pardo, et al. The Development of Gas Tight Thin Films of (La,Sr)(Ga,Fe)O3, (La,Sr)(Co,Fe)O3, and La2NiO4 for Oxygen Separation R. Muydinov, et al. Investigation into Thermal Expansion and Sintering of La2Mo4+d (Ln = La, Pr and M = Ni, Co) I.J.E. Brooks, et al. Oxide Ion Transport in Novel K2NiF4-Type Oxides C.N. Munnings, et al. Conductivity and Electronic Structure of Lanthanum Nickelites A.V. Zyrin, et al. Defect Chemistry of Mixed Ionic/Electronic P-Type Oxides H.U. Anderson, et al. Authors Index. Notes.

Crack bifurcation features in laminar specimens with fixed total thickness

A method to analyze the crack bifurcation behavior of symmetric two-component layered composites had been developed. With the method it is possible to compute the layer thickness at which cracks bifurcate. The thickness necessary for cracks to bifurcate depends on the elastic constants of the layers, the number of layers, the difference of thermal expansion coefficients and the temperature gradient. Further, the thickness ratios at which crack bifurcation can occur for layers with tensile and compressive residual stresses were computed. In the work the important case of specimens with fixed total thickness is considered. There are some features of crack bifurcation under these conditions. # 2002 Elsevier Science Ltd. All rights reserved.

Mechanical properties of ZrB2–SiC ceramic composites: room temperature instantaneous behaviour

Abstract Abstract The mechanical properties of ZrB2–30 wt-%SiC ultra high temperature ceramic composites have been studied. The composite was processed by hot pressing at 2100°C, 30 MPa and 45 min dwell time to achieve a good densification. Young’s modulus, single edge V notch beam fracture toughness, hardness, stress–strain deformation, four-point bending strength and Weibull parameters were measured. Fractography and microstructure analyses of ZrB2–30 wt-%SiC ceramic composite were also performed.

Phase Stability and Sintering Behavior of 10mol%Sc2O3–1mol%CeO2–ZrO2 Ceramics

The phase composition and sintering behavior of two commercially available 10 mol % Sc 2 O 3 -1 mol % CeO 2 -ZrO 2 ceramics produced by Daiichi Kigenso Kagaku Kogyo (DKKK) and Praxair have been studied. DKKK powders have been manufactured using a wet coprecipitation chemical route, and Praxair powders have been produced by spray pyrolysis. The morphology of the powders, as studied by scanning electron microscopy, has been very different. DKKK powders were presented as soft (∼100 μm) spherical agglomerates containing 60-100 nm crystalline particles, whereas the Praxair powders were presented as sintered platelet agglomerates, up to 30 μm long and 3-4 μm thick, which consisted of smaller 100-200 nm crystalline particles. X-ray diffraction analysis has shown that both DKKK and Praxair powders contained a mixture of cubic (c) and rhombohedral (r) phases: 79% cubic +21% rhombohedral for DKKK powders and 88% cubic +12% rhombohedral for Praxair powders. Higher quantities of the Si impurity level have been detected in Praxair powder as compared to DKKK powder by secondary ion mass spectroscopy. The morphological features, along with differences in composition and the impurity level of both powders, resulted in significantly different sintering behaviors. The DKKK powders showed a more active sintering behavior than of Praxair powders, reaching 93-95% of theoretical density when sintered at 1300°C for 2 h. Comparatively, the Praxair powders required high sintering temperatures at 1500-1600°C. However, even at such high sintering temperatures, a significant amount of porosity was observed. Both DKKK and Praxair ceramics sintered at 1300°C or above exist in a cubic phase at room temperature. However, if sintered at 1100 °C and 1200°C, the DKKK ceramics exist in a rhombohedral phase at room temperature. The DKKK ceramics sintered at 1300° C or above exhibit cubic to rhombohedral and back to cubic phase transitions upon heating at a 300-500°C temperature range, while Praxair ceramics exist in a pure cubic phase upon heating from room temperature to 900° C. However, if heated rather fast, the cubic to rhombohedral phase transformation could be avoided. Thus it is not expected that the observed phase transitions play a significant role in developing transformation stresses in SCCeZrO 2 electrolyte upon heating and cooling down from the operation temperatures.

Macrostructural engineering of ceramic-matrix layered composites

Abstract A method of computer simulation of the fracture of layered composites during a 3-point bending test is developed. A model of failure is considered which can be applied to two-component brittle layered composites (in particular ceramic-matrix composites). This particular model is executed for composites with the number of layers N=3, 7 and 15. The model is applied for the description of mechanical behaviour of two-component ceramic-matrix layered composites. The trends of the theoretical calculations agree with data obtained from 3-point bending test of real ceramic-matrix layered composites.

Enhanced Photoelectrocatalytic Reduction of Oxygen Using Au@TiO2 Plasmonic Film

Novel Au@TiO2 plasmonic films were fabricated by individually placing Au nanoparticles into TiO2 nanocavity arrays through a sputtering and dewetting process. These discrete Au nanoparticles in TiO2 nanocavities showed strong visible-light absorption due to the plasmonic resonance. Photoelectrochemical studies demonstrated that the developed Au@TiO2 plasmonic films exhibited significantly enhanced catalytic activities toward oxygen reduction reactions with an onset potential of 0.92 V (vs reversible hydrogen electrode), electron transfer number of 3.94, and limiting current density of 5.2 mA cm-2. A superior ORR activity of 310 mA mg-1 is achieved using low Au loading mass. The isolated Au nanoparticle size remarkably affected the catalytic activities of Au@TiO2, and TiO2 coated with 5 nm Au (Au5@TiO2) exhibited the best catalytic function to reduce oxygen. The plasmon-enhanced reductive activity is attributed to the surface plasmonic resonance of isolated Au nanoparticles in TiO2 nanocavities and suppressed electron recombination. This work provides comprehensive understanding of a novel plasmonic system using isolated noble metals into nanostructured semiconductor films as a potential alternative catalyst for oxygen reduction reaction.

Inelastic deformation behavior of La0.6Sr0.4FeO3 perovskite

Inelastic deformation behavior of the rhombohedral La0.6Sr0.4FeO3 perovskite is reported. Such behavior is very similar to the ferroelastic deformation of LaCoO3 or lead zirconate titanate perovskites, except that no twin structure was found to exist in La0.6Sr0.4FeO3. The possible mechanisms responsible for such nonlinear deformation behavior are discussed.