TaZr2.75O8 ceramics as a potential thermal barrier coating material for high-temperature applications.

• A series (1-x)ZrO 2 - x TaO 2.5 ceramics are synthesized by solid state reaction. • The final product of 0.72ZrO 2 -0.28TaO 2.5 is mainly composed of TaZr 2.75 O 8. • TaZr 2.75 O 8 has good mechanical properties and excellent phase stability. • Thermal conductivity of the TaZr 2.75 O 8 bulk is lower than that of YSZ. • TaZr 2.75 O 8 has a moderate thermal expansion coefficient, around 9.14 × 10−6 K−1. A series of TaO 2.5 -doped ZrO 2 (1-x)ZrO 2 - x TaO 2.5 (x = 0.08, 0.15, 0.2 and 0.28) ceramics were synthesized by solid state reaction at 1600 °C for 20 h. XRD results reveal that no tetragonal ZrO 2 phase forms in the TaO 2.5 –ZrO 2 system. Instead, a mixture of monoclinic ZrO 2 (m -ZrO 2) and orthorhombic TaZr 2.75 O 8 can be detected for (1-x)ZrO 2 - x TaO 2.5 ceramic within compositions x ≤ 0.2. As the doping content increases, the content of m -ZrO 2 decreases and the final product in the composition of 0.72ZrO 2 -0.28TaO 2.5 is primarily composed of TaZr 2.75 O 8. Microstructure together with the thermophysical and mechanical properties of TaZr 2.75 O 8 ceramic were investigated for possible applications as thermal barrier coatings (TBCs). The thermal conductivity with a minimum value of 1.65 W/m·K at 800 °C for TaZr 2.75 O 8 ceramic is ∼30% lower than that of dense YSZ and the dense ceramic also has a moderate average thermal expansion coefficient (TEC), about 9.14 × 10−6 K−1 from room temperature (RT) to 1300 °C. Besides, TaZr 2.75 O 8 exhibits a high microhardness (11.85 ± 0.42 GPa) and fracture toughness (3.15 MPa·m1/2). These preliminary results indicate that TaZr 2.75 O 8 can be used as an alternative material for the ceramic layer in TBCs system with respect to its superior thermal and mechanical properties. [ABSTRACT FROM AUTHOR]