Influence of partial substitution of Sc2O3 with Gd2O3 on the phase stability and thermal conductivity of Sc2O3-doped ZrO2

Multi-rare earth elements doping is one of effective methods to improve the phase stability and thermal barrier property of zirconia for thermal barrier coatings (TBCs) application. In this paper, the phase stability and thermo-physical properties of 7.5 mol% Sc2O3 and Gd2O3 co-doped ZrO2 (ScGdSZ) were investigated. ScGdSZ after 150 h heat-treatment at 1400 °C exhibited no monoclinic phase, showing high phase stability. The substitution of Sc2O3 with Gd2O3 increased the fraction of c-phase, however, t′-phase was still the dominant phase when the substitution amount was less than 2 mol%. The thermal conductivities of ScGdSZ gradually decreased with the increasing Gd2O3 proportion. 3.7 Sc2O3 and 3.7 Gd2O3 co-doped ZrO2 (in mol%) showed the lowest thermal conductivity, which was 20% lower than 7.5 Sc2O3-doped ZrO2 and 40% lower than 4.5 Y2O3-doped ZrO2.