Abstract
The a.c. and d.c. electrical conductivities of some hot-pressed polycrystalline nitrogen ceramics have been measured between 400 and 1000° C. The materials examined were Si3N4, 5.0% MgO/Si3N4 and two sialons, Si(6−z) · Al z · O z · N(8−z) having z ≈ 3.2 and z ≈ 4.0 respectively. The electrical behaviour of all the materials showed similar general features. The d.c. conductivities were about 10−10 Ω−1 cm−1 at 400° C and rose to between 10−6 and 10−5 Ω−1 cm−1 at 1000° C. The a.c. Data, taken over the frequency range 15 Hz to 5 kHz showed that below about 500° C the a.c. conductivity (σ a.c.) varied with frequency as σ a.c. ∝ ω s where 0.7 <s <1 indicative of a hopping process; in this temperature range the d.c. conductivity (σ d.c.) agreed well with the relation σ d.c. = A exp(−B/T 1/4). Above 700° C both the a.c. and d.c. conductivities followed log σ ∝ T −1. Hall effect and thermoelectric power measurements enabled the Hall mobility to be estimated as less than 10−4 cm2 V−1 sec−1 at 400° C and showed that the materials were all p-type below 900° C and n-type above 900° C. The electrical properties of all four materials are consistent with the presence of a glassy phase.
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Thorp, J.S., Sharif, R.I. Electrical conductivity in hot-pressed nitrogen ceramics. J Mater Sci 11, 1494–1500 (1976). https://doi.org/10.1007/BF00540883
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DOI: https://doi.org/10.1007/BF00540883