Person: Sparks, Taylor David
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Sparks
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Taylor David
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Sparks, Taylor David
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Publication Anisotropic Thermal Diffusivity and Conductivity in La-Doped Strontium Niobate Sr2Nb2O7(Wiley-Blackwell, 2010) Sparks, Taylor David; Fuierer, Paul A.; Clarke, DavidThe thermal diffusivity of the La-doped layered perovskite Sr2Nb2O7 parallel and perpendicular to the perovskite layers is reported from room temperature up to 1000°C. The anisotropy persists through an incommensurate-normal ferroelectric phase transformation at 215°C and up to 1000°C, the maximum temperature of our measurements. The thermal conductivity perpendicular to the perovskite layers, derived from the diffusivity in the same direction, calculated using the density and measured heat capacity, has a constant value of 1.05±0.05 W/mK up to 1000°C. Possible explanations for the low thermal conductivity and anisotropy are described.Publication Thermal Conductivity of the Rare-Earth Strontium Aluminates(Wiley-Blackwell, 2010) Wan, Chunlei; Sparks, Taylor David; Wei, Pan; Clarke, DavidThe thermal conductivity of a series of complex aluminates, RE2SrAl2O7, with different rare-earth (RE) ions, has been measured up to 1000°C. There is a strong dependence on the atomic number of the RE ion, ranging from an approximately 1/T dependence for the lanthanum strontium aluminate to an almost temperature-independent behavior of the dysprosium strontium aluminate. The latter conductivity is comparable with that of yttria-stabilized zirconia, the current material of choice for thermal barrier coatings. The temperature dependence of the thermal conductivities of all the aluminates studied can be fit to a standard phonon–phonon scattering model, modified to account for a minimum phonon mean free path, in which the difference in behavior is attributed to increased phonon–phonon scattering with the atomic mass of the RE ion. Although a satisfactory parametric fit is obtained, the model does not take into account either the detailed layer structure of the aluminates, consisting of alternating rock-salt and perovskite layers in a natural superlattice structure, or the site preferences of the RE ion. This suggests that further model development is warranted.