We use cookies to ensure that we give you the best experience on our website. By continuing to browse this repository, you give consent for essential cookies to be used. You can read more about our Privacy and Cookie Policy.

Durham e-Theses
You are in:

Electrical properties of hot-pressed nitrogen ceramics

Sharif, Rafiqul Aslam (1977) Electrical properties of hot-pressed nitrogen ceramics. Doctoral thesis, Durham University.



Some electrical properties of hot-pressed Si(_3)N(_4), 5 W/o MgO/Si(_3)N(_4) and two sialons, Si(_6-z). Al(_z).O(_z).N(_8-z) having Z = 3.2 and Z = 4.0 have been measured, using a variety of techniques, between 18 c and l000 C. The electrical behaviour of all the materials showed similar general features. The d.c. conductivities were in the range of 10(^-15)-10(^-16)Ω(^-1)cm(^-1) at 18 C and rose to 10(^-6)-10(^-5)Ω(^-1)cm(^-1) at 1000 C. The current density-field (J3-E) characteristics were ohmic in applied fields of less than 3 x 10(^3) volt cm(^-1), conductivity increased with electric field above that range. Above about 280 C, o(_dc) was independent of E, its temperature dependence following log o(_dc) aT(^-1). Below about 230 c conductivity fitted a o α exp ((^-B/)T(^1/4)) law in both low and high fields. The activation energies were in the range of 1.45-1.80 eV and 0.05-0.15 eV at above 300 C and near room temperatures respectively. Time dependent charging (I(_C)) and discharging (I(_D) currents were observed which followed a I(t)α t(^-n) law with n = 0.7-0.8 at room temperature. The exponent n for I(_C) decreased with increasing temperature. Hall effect and thermoelectric power measurements enabled the Hall mobility to be estimated as less than 10(^-4) cm(^2)v(^-1)sec(^-1) at above 400 C and showed that the materials were all p-type between 400 and 900 C and n-type above 900 C. The drift mobility obtained from observations of transit time effects was 1 x 10(^-8)-5 x 10(^-9) cm(^2)v(^-1)sec(^-1). Various hopping models to explain the data are considered. At room temperature the variation of conductivity (o’ (w) α w(^n) with frequency over the range 200 Hz to 9.3 GHz followed the o’(w) α w(^n) law with n = 0.9. The dielectric constant (Σ') and loss (tano) both fell slightly over this frequency range, the average values at 10(^5) Hz being about 9.5 and 5 X 10(^-3) respectively. At temperatures up to 500 C the data fits well with the 'Universal dielectric law' Σ"(w) α w(^n-1) and approximately fits the Kramers-Kronig relation Σ"(w)/(_Σ’(w) – Σ). = cot ((^nπ)/(_2)) with 0.5 < n < 1. The exponent n decreases with increasing temperature. The effects may be caused by either non-Debye dipolar or hopping charge phenomena. Similar studies of electrical properties for 30 m/o Li-sialon and 14.3 m/o Y-sialon were also made in an attempt to relate the electrical properties and compositions of pure and doped sialons.

Item Type:Thesis (Doctoral)
Award:Doctor of Philosophy
Thesis Date:1977
Copyright:Copyright of this thesis is held by the author
Deposited On:18 Sep 2013 15:53

Social bookmarking: del.icio.usConnoteaBibSonomyCiteULikeFacebookTwitter