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

Ln2Zr2O7 (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(Ln3+)/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 (εr′) and dielectric loss factor (εr″) 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 δ) was ascribed to the dopant-vacancy associate. The εr(0) and dielectric constant of the associate (εr0) showed also the maximum values at the vicinity of the phase boundary between the F- and P-type phases.