Electrical Properties of Yttria-Stabilized Zirconia, YSZ Single Crystal: Local AC and Long Range DC Conduction

Abstract

Widely-used complex plane analysis of impedance data is insufficiently sensitive to characterize fully the bulk properties of YSZ single crystal. Instead, more extensive data analysis is needed which uses a combination of parallel, admittance-based formalisms and series, impedance-based formalisms. Bulk electrical properties are measured at higher frequencies and contain contributions from both long range conduction and local dielectric relaxation. At lower frequencies, electrode-sample contact impedances are measured and are included in full equivalent circuit analysis. The impedance of YSZ crystal of composition 8 mol% Y 2 O 3 in the (110) orientation, with Pt electrodes, was measured over the temperature range 150-750 • C and frequency range 0.01 Hz-3 MHz. Full data analysis required (i) a parallel constant phase element (CPE)-resistance (R) combination to model the electrode response, (ii) a series R-C element to represent local reorientation of defect dipoles and (iii) a R-C-CPE element to represent long range oxide-ion conduction; (ii) and (iii) together model the bulk response. The dielectric element underpins all discussions about defect structure and properties of YSZ but has not been included previously in analysis of impedance data. The new equivalent circuit that is proposed should allow better separation of bulk and grain boundary impedances of YSZ ceramics. Yttria-stabilized zirconia (YSZ) is a very well-known oxide ion conductor that is used as the solid electrolyte in solid oxide fuel cells and oxygen gas sensors.1-3 It usually takes the form of a high-density ceramic in which the bulk resistance in series with a grain boundary resistance gives the overall sample resistance. 4 In almost all cases, the grain boundary resistance is present and cannot be eliminated readily by attention to ceramic processing conditions. The nature of the grain boundary impedance is often unclear, although significant compositional differences from the bulk, associated with dopant segregation, may be involved. 5,6 In order to measure sample impedances, sample-electrode contacts are necessary and therefore, appropriate consideration of their associated impedances forms part of the overall impedance analysis. For YSZ, contact impedances include contributions from the blocking of oxide ions at the sample-electrode interface, charge transfer resistances associated with the O 2− /O 2 redox couple and the diffusion of O 2 molecules between the surrounding atmosphere and the sampleelectrode interface. Usually, electrode contact impedances are wellseparated on a frequency scale from bulk/grain boundary impedances because they have much higher associated capacitances, C: typically (1-10) × 10 −6 F for the electrode contact compared with ∼ 1 × 10 −10 F for a grain boundary capacitance and (2-3) × 10 −12 F for a bulk capacitance. Relaxation frequencies, ω, are given ideally by ωτ = 1, where τ = RC and therefore, the frequency maxima of impedance semicircles, arcs or peaks associated with bulk/grain boundary impedances are usuall...

Field-induced p-n transition in yttria-stabilized zirconia

“…3 for impedance measurements at (a) 610 and (b) 800 °C in dry N 2 [ p O 2 ∼ (1–2)x10 −4 atm] and at (c) 800 °C in dry O 2 [ p O 2 ∼1 atm]. Data at 610 °C show a broad impedance arc which, from accurate fitting to the equivalent circuit shown as the inset in (a), contains as the major component, the bulk dc resistance, R 1 of the sample together with a parallel resistance, R 2 associated with a dipole relaxation process 42 , Figs. S1–S3 and Table S1.…”

CO Oxidation on Ceria Studied by Electrochemical Impedance Spectroscopy

“…Corrected data were analyzed and modelled using Zview (Scriber Associates Inc.) software. Details of the impedance analysis can be found extendedly in the literature [39,50–53] . For the sake of convenience, we have added a brief introduction to EIS and to the analysis of EIS data in the supplementary information file.…”

Realistic dielectric response of high temperature sintered ZnO ceramic: a microscopic and spectroscopic approach

“…However, Z* plot on linear scale offers unnecessary weighting to the largest resistances in a sample and effectively ignores from view the conductive grain cores surrounded by resistive grain boundaries. 54 A comprehensive analysis of impedance data that sidesteps such weighting is presented by demonstrating the same impedance data in at least two of the four formalisms: impedance Z*, admittance Y*, electric modulus M* and permittivity 3*.…”

“…Log Y 0 vs. log f plot provides an equivalent credit to the different conducting elements and in particular emphasizes the existence of a high frequency dispersion modeled by the bulk constant phase element (CPE). 54 Fig. 6 shows admittance or conductivity plot (log Y 0 vs. log f) for ZnO sintered samples.…”