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The thermal and electrical transport properties of various spark plasma-sintered HfB 2 -and ZrB 2 -based polycrystalline ceramics were investigated experimentally over the 298-700 K temperature range. Measurements of thermal diffusivity, electrical resistivity, and Hall coefficient are reported, as well as the derived properties of thermal conductivity, charge carrier density, and charge carrier mobility. Hall coefficients were negative confirming electrons as the dominant charge carrier, with carrier densities and mobilities in the 3-5 Â 10 21 cm À3 and 100-250 cm 2 . (V . s) À1 ranges, respectively. Electrical resistivities were lower, and temperature coefficients of resistivity higher, than those typically reported for HfB 2 and ZrB 2 materials manufactured by the conventional hot pressing. A Wiedemann-Franz analysis confirms the dominance of electronic contributions to heat transport. The thermal conductivity was found to decrease with increasing temperature for all materials. Results are discussed in terms of sample morphology and compared with data previously reported in the scientific literature.

We evaluated the thermal conductivity of HfB 2 -based ultra-hightemperature ceramics from laser flash diffusivity measurements in the 251-6001C temperature range. Commercially available powders were used to prepare HfB 2 composites containing 20 vol% SiC, some including TaSi 2 (5 vol%) and Ir (0.5 or 2 vol%) additions. Samples were consolidated via conventional hot pressing or spark plasma sintering. Processing differences were shown to lead to differences in magnitude and temperature dependence of effective thermal conductivity. We compared results with measured values from heritage materials and analyzed trends using a network model of effective thermal conductivity, incorporating the effects of porosity, grain size, Kapitza resistance, and individual constituent thermal conductivities.Y. Blum-contributing editor J. Marschall's contributions were