Dielectric properties of some hot-pressed nitrogen ceramics

The dielectric properties of some hot-pressed nitrogen ceramics have been measured at room temperature over the frequency range 200 Hz to 75 MHz and also at 9.3 GHz; low frequency measurements were also made at temperatures up to 500° C. The materials examined were Si₃N₄, 5.0 wt % MgO/Si₃N₄ and two sialons Si_(6–z)·Al_z·O_z·N_(8–z) havingz = 4.0 and 3.2 respectively. At room temperature, the variation of the real part of the conductivity with frequency over the range 200 Hz to 9.3 GHz followed () ⁿ, withn = 0.9. The dielectric constant , and loss tan , both fell slightly over this frequency range, the average values at 10⁵ Hz being about 9.5 and 5.5 × 10^–3, respectively. The data fits well with the universal dielectric law, ^–1 (n < 1) and approximately fits the Kramers-Kronig relation ()/(() – = cot(n/2). This behaviour applies also at temperatures up to 500° C except that the value ofn decreases as the temperature increases. The effects may be caused by either dipolar or hopping charge phenomena.