RESEARCH SPOTLIGHT: Metals – Solid Oxide Fuel Cells, Shape Memory, Toughening

Описание: Investigating the Effects of Aliovalent Doping on the Phase Transformation and Thermal Expansion Properties of Rare Earth Orthoniobate Materials

Rare earth orthoniobate materials are interesting candidates for proton conducting solid oxide fuel cell, shape memory, and transformation toughening applications. The rare earth niobates are known to undergo a reversible pure second order ferroelastic phase transformation from a low temperature monoclinic structure to a high temperature tetragonal structure. For proton conduction and toughening applications it is preferable to have the material in the high temperature tetragonal structure, as such a thorough understanding of the phase transformation and thermal expansion behavior of these materials is needed. Two doping strategies were investigated in pursuit of this understanding. First, aliovalent doping of lanthanum and dysprosium niobates by partial replacement of the rare earth cation with 2+ valency alkaline earth cations and secondly, co-substitution of the rare earth and niobium cations with zirconium. The purpose of this study was to understand the effect of these doping strategies on the phase transformation and thermal expansion properties of lanthanum niobate, yttrium niobate, and dysprosium niobate materials. To study these material properties differential scanning calorimetry and in situ high temperature x-ray diffraction methods were utilized. These experimental methods are uniquely suited to study the rare earth niobates due to the second order phase transformation, which cannot be stabilized through quenching, and the highly anisotropic thermal expansion behavior due to the low symmetry monoclinic crystal structure. Insights into the phase transformation and thermal expansion properties of these materials will be presented as a function of composition and temperature.

PRESENTED BY
Daniel R. Lowry, Ph.D.