Electrical resistivity of ZrCx is plotted as a function of temperature in Figure 16. Room temperature resistivity ranges from 60 to 200 pQ cm, depending on C/Zr ratio and microstructure. In an intermediate temperature range from approximately 100 to 2000 K, resistivity increases linearly with temperature.45,46,56,57 Modine et a/58 measured resistivity of single crystal ZrCx (x = 0.89, 0.93, and 0.98) between 4 and 1000 K. The authors deemed the data well represented by the Bloch-Gruneisen model for temperature depen­dence of resistivity of metals, with resistivity varying as T5 at low temperatures (4-100 K) and linearly at intermediate temperatures. At a high enough tem­perature (1000-2000 K), resistivity deviates from linear behavior and tends to saturate at a constant value which decreases with C/Zr ratio. The higher — temperature measurements on single-crystal ZrC0.93 of Hinrichs et a/.59 are consistent with the trend established for single crystal ZrC0.93 at lower tem­peratures by Modine et a/. (Figure 16).

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Temperature (K)

Figure 16 Electrical resistivity of ZrCx as a function of temperature.

The resistivity of single crystals exceeds that of polycrystals up to 2200-2500 K where the former begins to saturate; resistivity of polycrystalline ZrCx saturates only near the melting temperature, although few measurements have been made in this tempera­ture range. The effects of free carbon and oxygen/ nitrogen impurities on resistivity have not been explored. Measurements on pyrolytic ZrCx53 lie in the same range as those of other polycrystalline speci­mens, but a detailed study of the effects of grain size, texture, porosity, and other microstructural factors on electrical resistivity is needed.

Room temperature electrical resistivity as a function of C/Zr ratio is plotted in Figure 17. Resis­tivity is lowest for near-stoichiometric compositions and increases with deviation from stoichiometry. A decrease in C/Zr ratio increases the concentration ofcarbon vacancies, which scatter conduction electrons. Storms and Wagner35 fit the available experimental data to the formula 1 1

0.00382 +

55 + where p is electrical resistivity (p. Q cm) and x is C/Zr ratio, which is plotted in Figure 17.