Relationship between oxide-ion conductivity and dielectric relaxation in the Ln2Zr2O7 system having pyrochore-type compositions (Ln = Yb, Y, Gd, Eu, Sm, Nd, La)

Ln(2)Zr(2)O(7) (Ln = Yb, Y, Gd, Eu, Sm, Nd, La) system changed from fluorite (F)-type to pyrochlore (P)-type phases when the ionic radius ratios, r(Ln(3+))/r(Zr4+), were larger than 1.26. The oxide-ion conductivity showed sharp maximum at the vicinity of the phase boundary between the F- and P-type phases. The frequency dependence of dielectric constant (epsilon'(r)) and dielectric loss factor (epsilon ''(r)) were successfully explained by the superimposition of Debye-type polarization due to dopant-vacancy associate and electrode-electrolyte interfacial polarization by the numerical calculation. The peak of dielectric loss tangent (tan delta) was ascribed to the dopant-vacancy associate. The epsilon(r)(0) and dielectric constant of the associate (epsilon(r0)) showed also the maximum values at the vicinity of the phase boundary between the F- and P-type phases. (C) 2008 Elsevier Ltd. All rights reserved.