Abstract
Electrical relaxation in the (CeO 2) 1− x -(Y 2O 3) x [where x = 0 to 0.2] system has been studied as a function of temperature (~ 100–600°C) using the electric modulus formalism in the frequency range 5–10 7 Hz. Two relaxation processes are observed in low Y 2O 3 (up to ~2 m o ) doped samples. One is due to long range migration of free oxygen vacancies (Process A) and the other is due to orientation relaxation of the (Y CeV o) . charged associated defects (Process B). The conductivity relaxation process is analysed using the non-exponential decay function φ(t) = exp[−( t τ o ) gb] for 0 < β ⩽ 1 , of the electric field. The relaxation parameters of undoped CeO 2 do not change with temperature suggesting the vacancies are frozen-in on cooling pure CeO 2 from sintering temperatures so guaranteeing the vacancy concentration does not change at the experimental temperatures used for the modulus studies. Undoped CeO 2 has a relaxation process close to a single relaxation but, with increasing dopant concentration, the electric modulus relaxation peak broadens. The observed activation enthalpy minimum (activation enthalpy vs m o Y 2O 3) for Process A is explained using the concept of partial dissociation of V ö o from (Y Ce V O) . defect associates and formation of higher-order defect clusters at higher m o Y 2O 3 .
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