Elevated temperature electrical resistivity measurements of zirconium diboride using the van der Pauw Method

A novel electrical testing assembly was designed, fabricated, and validated to allow elevated temperature electrical resistivity measurements using the van der Pauw method up to 2173 K. The assembly consisted of h-BN insulators, ZrB2-based fixture components, and W signal wires. The assembly was installed in a refractory metal element furnace for temperature control and an oxygen gettering system was utilized to control the oxygen activity of the process gas. The system was validated using high-purity Mo as a reference standard, demonstrating good agreement with accepted electrical resistivity values for Mo. The system was utilized to measure the electrical resistivity of a ZrB2 ceramic that was produced from commercially available ZrB2 powder using C and ZrH2 as sintering aids and densified by hot-pressing at 2423 K. The resulting ZrB2 ceramic was ~96% dense with ~0.2 wt.% ZrO2 secondary phase and a grain size of ~40 mu m. Electrical resistivity of ZrB2 was measured from room temperature to 2133 K. The electrical resistivity of the ZrB2 exhibited distinct linear behavior with respect to temperature, increasing from 7.3 mu omega-cm at 298 K to 35.7 mu omega-cm at 1223 K (~0.031 mu omega-cm/K), and then further increasing to 76.0 mu omega-cm at 2133 K (~0.044 mu omega-cm/K). To the knowledge of the authors, these measurements were performed at the highest temperatures ever reported using this method.