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Sökning: WFRF:(Ivanova A) > Linköpings universitet

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2.
  • Ivanova, Mariya E., et al. (författare)
  • Functional properties of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ proton conductors where X is an alkaline earth cation
  • 2015
  • Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 35:4, s. 1239-1253
  • Tidskriftsartikel (refereegranskat)abstract
    • Lanthanum niobates with general formulas of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ (X = Mg, Ca, Sr or Ba) were synthesized via the conventional solid state reaction. Specimens with relative density above 96% were produced after sintering. Structural and phase composition studies revealed predominant monoclinic Fergusonite structure for the majority of samples. SEM and TEM studies elucidated the effect of the used dopant combinations on grain growth, micro-crack formation and secondary phase formation. Results from microstructural study were correlated to the grain interior and grain boundary conductivities for selected samples (La0.99Sr0.01Nb0.99Al0.01O4−δ and La0.99Sr0.01Nb0.99Ti0.01O4−δ). The majority of co-doped niobates exhibited appreciable protonic conductivity under humid atmospheres at intermediate temperatures. Sr- or Ca-doped compounds displayed the highest total conductivities with values for LSNA equal to 6 × 10−4 S/cm and 3 × 10−4 S/cm in wet air and in wet 4% H2–Ar (900 °C), respectively. Additionally, thermal expansion was studied to complete functional characterization of co-doped LaNbO4.
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3.
  • Palisaitis, Justinas, et al. (författare)
  • Phase homogeneity analysis of La0.99Sr0.01Nb0.99Al0.01O4−δ and La0.99Ca0.01Nb0.99Ti0.01O4−δ proton conductors by high-resolution STEM and EELS
  • 2015
  • Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 35:5, s. 1517-1525
  • Tidskriftsartikel (refereegranskat)abstract
    • The microstructural and compositional homogeneity of La0.99Ca0.01Nb0.99Ti0.01O4−δ and La0.99Sr0.01Nb0.99Al0.01O4−δ proton conductors was studied using the combination of atomic-resolution scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) and STEM image simulations. The obtained results revealed that gently doped proton conductors were predominantly composed of grains with a monoclinic lanthanum niobate crystal structure. In addition to the host phase, dopant-rich phases were also observed and identified. The La0.99Sr0.01Nb0.99Al0.01O4−δ matrix accommodated dopant-rich grains retaining an LaAlO3 cubic crystal structure with a significant fraction of Sr incorporated into them. The secondary phases embedded in the La0.99Ca0.01Nb0.99Ti0.01O4−δ matrix possessed the pyrochlore La2Ti2O7 crystal structure with Ca partially substituting La. High spatial resolution EELS revealed preferential Ca sites within the pyrochlore La2Ti2O7 crystal lattice. The origin of the secondary phase formation and the role of these phases for the transport properties of co-doped lanthanum niobates are discussed here.
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