Improvement on thermophysical and mechanincal properties of LaMgAl11O19 magnetoplumbite by Nd2O3 and Sc2O3 co-doping

Abstract

LaMgAl11O19-type magnetoplumbite holds great promise to be used above 1300 °C as thermal barrier coatings (TBCs), but its practical application has been restricted because of inferior thermophysical properties. Herein, we focus on optimizing the thermophysical properties of LaMgAl11O19 by simultaneously substituting La3+ and Al3+ ions with Nd3+ and Sc3+ ions, respectively. Results show that the effects of co-substitution on reducing thermal conductivity are pronounced. The thermal conductivities of La1-xNdxMgAl11-xScxO19 (x = 0, 0.1, 0.2, 0.3) ceramics decrease progressively with dopant concentration and a lowest thermal conductivity of 2.04 W/(m·K) is achieved with x = 0.3 at 1000 °C, which is a value superior to pure LMA and even lower than YSZ. The mechanisms behind the lowered thermal conductivity are investigated. Increase of the thermal expansion coefficient is also realized (8.53 × 10−6 K−1 for pure LMA, 9.07 × 10−6 K−1 for x = 0.3, 1300 °C). Most importantly, Nd3+ and Sc3+ combination doping indeed facilitates mechanical properties of La1-xNdxMgAl11-xScxO19 solid solutions as well. It should be noted that Sc3+ doping at Al3+ site plays more effective role in improving thermal properties than Nd3+ does at La3+ site. This work provides a path to simultaneously integrate low thermal conductivity, good phase stability, moderate thermal expansion behavior and excellent mechanical properties on LMA for the next generation TBCs.