Synthesis and phase stability of the ZrO2-(Y2O3, Nd2O3)-Ta2O5 compositions for high tetragonality zirconia-based thermal barrier coatings

As a part of a new thermal barrier coating (TBC) material development projects some co-doped compositions were proved to be very promising. Usually in the co-doped compositions the primary component is yttria and the secondary is rare-earth oxide, both components being stabilizers for zirconia. These compositions were shown to be effective in decreasing thermal conductivity, but their fracture toughness was decreased too. On that reason there is a trend on zirconia doping with destabilizing oxides to increase the tetragonality index and have low thermal conductivity at the same time.

The present paper focuses on the co-precipitation synthesis and properties of the yttrium (YTaO₄) or neodymium (NdTaO₄) tantalate powder and tantalate-stabilized zirconia powders ZrO₂-YTaO₄ or ZrO₂-NdTaO₄. Their phase composition was investigated at different calcination temperatures. Both yttrium and neodymium tantalates were shown to have two types of monoclinic structures (M and M’). As to zirconia-based compositions, both single and multi-phase samples were obtained depending on the tantalate amount and calcination temperature. Tetragonality indexes up to 1,027 were obtained.