Aliovalent doping of La2Zr2O7 with Al³ ⁺ and Ta⁵⁺ for CTE tuning

In this work, the influence of aliovalent doping with Al 3 + and Ta 5+ cations on the structure and thermal properties of La 2 Zr 2 O 7 (LZO) was investigated and the solubility of Al 3+ and Ta 5+ in LZO separately and jointly was studied for the first time. The samples were synthesized by mechanochemical activation followed by sintering at 1200 °C and 1500 °C. It was established that doping maintains the pyrochlore-type structure (space group Fd 3 ¯ m ) within observed solubility limits (Al 3+ up to x ≈ 0.12 and Ta 5+ up to y ≈ 0.48). While the CTE of pure LZO increases with temperature (from 7.97 at 25°C to 11.50 ×10⁻⁶ °C⁻¹ at 1300°C), co-doping with Al 3+ and Ta 5+ , specifically for the La 1.96 Al 0.09 Ta 0.25 Zr 1.7 O 7.075 composition, resulted in a remarkably stable CTE (from 9.09 at 25°C to 9.82 ×10⁻⁶ °C⁻¹ at 1300°C) over a wide temperature range, a critical factor for thermal barrier coatings.