Characterisation of conductivity of the (Ce xY0.2-x)Sc0.6 Zr3.2O8-δ (0 < x < 0.2) system and composition Ce0.04Y0.02Sc0.67Zr3.27O 7.66 as function of time

Abstract

EXPERIMENTALThe powders were prepared by a sol-gel combustion method [12]. Scandia powders (TTE Metals, 99.9% purity) were dissolved in nitric acid (Fisher Scientific, 70%) and hydrogen peroxide (Fisher Scientific, N30% wv). Separately, cerium (III) nitrate hexahydrate (Aldrich, 99% purity), AbstractThe conductivity behaviour of the (Ce x Y 0.2-x )Sc 0.6 Zr 3.2 O 8-d (0 ≤ x ≤ 0.2) system and composition Ce 0.04 Y 0.02 Sc 0.67 Zr 3.27 O 7.66 have been investigated as function of time using impedance spectroscopy. All samples were prepared by sol-gel and combustion process, sintered at 1500 °C for 12 h and the densities obtained were between 92 and 97%. The electrical measurements were performed at 600 °C. The conductivity values were fairly stable during the first 1800 h of the experiment but after this time the conductivity decreases. For some compositions of the system a semi-circle is detected through time, with capacitance values of an order of magnitude lower, 10 -8 F/cm. This semi-circle becomes well defined with time. After the experiment, SEM pictures show that grain boundary is well defined and an increase of pore inside grains, in some cases the surface is damaged showing cracks and fissures indicating microstructure deterioration. Keywords: scandia-zirconia, ac impedance, ageing. Resumo