Synthesis and Thermophysical Properties of La₂Zr₂O₇/SrZrO₃ Composite as a New Thermal Barrier Coating Material

The La₂Zr₂O₇/SrZrO₃ composite with a mol ratio of 1:2 named (La_0.5Sr_0.5)ZrO_3.25 (LSZ) was in-situ synthesized by co-precipitation method using ammonia and ammonium oxalate as precipitants. The synthesized LSZ powder showed good phase stability not only from room temperature to 1400°C but also at higher temperature of 1450°C for a long period, as analyzed by thermogravimetry, differential scanning calorimetry and X-ray diffraction, respectively. The bulk LSZ with relative density >95% was prepared by pressureless sintering at 1500°C for 2 h and spark plasma sintering (SPS) at 1300°C for 5 min, respectively. The fracture toughness of the bulk LSZ prepared by both pressureless sintering and SPS were 1.80±0.20 MPa·m^1/2 and 1.95±0.09 MPa·m^1/2, respectively, which are higher than that of both bulk SrZrO₃ and La₂Zr₂O₇. The coefficients of thermal expansion (CTEs) of the bulk LSZ were 8.4-9.5×10^-6 K^-1 in a temperature range of 200-1200°C, which are higher than that of La₂Zr₂O₇ but lower than that of SrZrO₃. The thermal conductivity of the bulk LSZ prepared by pressureless sintering was ~1.1 W·m^-1·K^-1 at 1000°C, which is lower than that of both bulk SrZrO₃ and La₂Zr₂O₇. The LSZ composite is considered as a promising thermal barrier coating material.