Influence of additives on phase stabilization of scandia-doped zirconia

Eliana Navarro Dos Santos Muccillo,Shirley Leite Dos Reis,Reginaldo Muccillo,Robson Lopes Grosso

doi:10.1590/s1517-707620170002.0154

Abstract

The effects of small additions of tin, zinc, calcium and boron oxides on phase composition and electrical conductivity of zirconia-10 mol% scandia were investigated. Compounds containing 1 mol% zinc, tin and calcium oxides and 1, 3 and 5 wt.% boron oxide were prepared by solid state reaction and characterized by X-ray diffraction, density measurements, scanning electron microscopy and impedance spectroscopy. Full stabilization of the cubic structure at room temperature was obtained with additions of 1 mol% calcium oxide and 2 wt.% boron oxide. Partially stabilized compounds exhibit herringbone structure, characteristic of the β-rhombohedric phase. Specimens with calcium as additive show total conductivity of 23.8 mS.cm-1 at 750ºC with activation energy of 1.13 eV. Liquid phase sintering by boron oxide addition is effective to enhance the densification of the solid electrolyte.

Highlights

Full stabilization of the cubic structure at room temperature was obtained with additions of 1 mol% calcium oxide and 2 wt.% boron oxide
The combination of high ionic conductivity, wide electrolytic domain and low electronic conductivity turns the scandia stabilized zirconia, ScSZ, solid electrolyte a promising candidate for replacing yttria stabilized zirconia for application in solid oxide fuel cells operating at intermediate temperatures, typically 800oC [1-3]
Small amounts of tin, zinc and calcium oxides as phase stabilizer, and boron oxide as sintering aid were added to zirconia-10 mol% scandia and their effects on structure, microstructure and ionic conductivity were investigated

Summary

INTRODUCTION

The combination of high ionic conductivity, wide electrolytic domain and low electronic conductivity turns the scandia stabilized zirconia, ScSZ, solid electrolyte a promising candidate for replacing yttria stabilized zirconia for application in solid oxide fuel cells operating at intermediate temperatures, typically 800oC [1-3]. It was found that the cubic phase transforms on the surface of the solid electrolyte to monoclinic via tetragonal phase during operation at 900oC of a tubular-type SOFC [13]. Conductivity degradation of this electrolyte was observed at 600oC during long-term operation in humidified mixture of H2/N2 and humidified H2 [14]. Small amounts of tin, zinc and calcium oxides as phase stabilizer, and boron oxide as sintering aid were added to zirconia-10 mol% scandia and their effects on structure, microstructure and ionic conductivity were investigated

Materials preparation

RESULTS AND DISCUSSION

CONCLUSIONS