Browsing by Author "Gaskins, John T."

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    On the thermal and mechanical properties of Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O across the high-entropy to entropy-stabilized transition
    Rost, Christina M.; Schmuckler, Daniel L.; Bumgardner, Clifton; Bin Hoque, Md Shafkat; Diercks, David R.; Gaskins, John T.; Maria, Jon-Paul; Brennecka, Geoffrey L.; Li, Xiadong; Hopkins, Patrick E. (AIP Publishing, 2022-12-16)
    As various property studies continue to emerge on high entropy and entropy-stabilized ceramics, we seek a further understanding of the property changes across the phase boundary between "high-entropy"and "entropy-stabilized"phases. The thermal and mechanical properties of bulk ceramic entropy stabilized oxide composition Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O are investigated across this critical transition temperature via the transient plane-source method, temperature-dependent x-ray diffraction, and nano-indentation. The thermal conductivity remains constant within uncertainty across the multi-to-single phase transition at a value of ≈2.5 W/mK, while the linear coefficient of thermal expansion increases nearly 24% from 10.8 to 14.1 × 10-6 K-1. Mechanical softening is also observed across the transition.
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    Size Effects on the Cross-Plane Thermal Conductivity of Transparent Conducting Indium Tin Oxide and Fluorine Tin Oxide Thin Films
    Olson, David H.; Rost, Christina M.; Gaskins, John T.; Szwejkowski, Chester J.; Braun, Jeffrey L.; Hopkins, Patrick E. (IEEE, 2018-08-06)
    Visibly transparent and electrically conductive oxides are attractive for a wide array of applications. Indium tin oxide (ITO) and fluorine tin oxide (FTO) are the subset of the larger transparent conducting oxide family and possess transmittance in the visible spectrum as well as high electrical conductivity. Even though their unique optical and electrical properties have been thoroughly examined, the thermal transport properties, namely, thermal conductivity in the cross-plane direction, have received much less attention. In this paper, using a series of ITO and FTO thin films comprising a range of thicknesses and grain sizes, we characterize the cross-plane thermal conductivity using time-domain thermoreflectance. We determine the heat capacity of the FTO films from simultaneous measurements of volumetric heat capacity and thermal conductivity on an 396-nm-thick FTO film. We show that the size effects have a considerable influence on the thermal conductivity from both the perspective of grain boundary and thin film scattering.