Microstructure and ionic conductivity of SrTiO3 heterogeneously doped YSZ composite ceramics

Abstract

To improve the ionic conductivity of ZrO 2 stabilized by 8 mol% of Y 2 O 3 (8YSZ), the SrTiO 3 heterogeneously doped 8YSZ composite ceramics with different volumetric fractions of SrTiO 3 were prepared through powder sintering at 1400 °C and 1450 °C in air. The phase compositions, microstructures, electrical conductivities and ion transference numbers of the composites were investigated by X-ray diffraction, scanning electron microscopy, complex impedance and Hebb–Wagner polarization method, respectively. The composite ceramics only consist of cubic YSZ and SrTiO 3 . The deviations of the typical diffraction peak positions in XRD spectra and the variations in unit cell parameters of both SrTiO 3 and YSZ in composites have occurred due to the elemental inter-diffusion between both phases. The grain boundaries between these two heterogeneous phases do not exhibit any presence of a segregated impurity phase, and the heterogeneous doping of SrTiO 3 can suppress the growth of YSZ grains at higher doping levels. The apparent conductivities of the composites show a peak at 5 vol.% of SrTiO 3 addition. The activation energies for the oxygen ion transport of 8YSZ doped with 0–15 vol.% of SrTiO 3 all fall into the range of 101.71–104.93 kJ/mol. The ion transference numbers of the composites with 1–15 vol.% of SrTiO 3 are all higher than 0.99, demonstrating that the electrical conductivity is almost pure ionic in nature. By analyzing the effects of SrTiO 3 additions on the normalized conductivities of the composites, the SrTiO 3 /YSZ heterogeneous interfacial effects on the conductivity improvement can be proposed. • SrTiO 3 heterogeneously doped 8YSZ composites are prepared by sintering in air. • Elemental diffusions between SrTiO 3 and YSZ occur after powder sintering. • The SrTiO 3 /YSZ heterogeneous interface can enhance the conductivity of composites. • Electrical conductivities of YSZ doped with 1–15 vol.% of SrTiO 3 are ionic in nature.