Reactive spark plasma sintering of high-entropy (La1/7Nd1/7Sm1/7Eu1/7Gd1/7Dy1/7Ho1/7)2Zr2O7 pyrochlore ceramic

In this work, an efficient method for the synthesis of high-entropy pyrochlore ceramic (La1/7Nd1/7Sm1/7Eu1/7Gd1/7Dy1/7Ho1/7)2Zr2O7 (7RE2Zr2O7) was developed via reactive spark plasma sintering. The sintering reactivity, phase composition, microstructure, and mechanical properties of 7RE2Zr2O7 were systematically investigated. With the aid of uniaxial pressure and direct current (DC) pulse voltage, the entire sintering process was greatly shortened to less than 1 h. Owing to the synergistic effects of the compositional complexity and severe lattice distortion, 7RE2Zr2O7 exhibited a reduced average grain size of only 1.45 μm, which is approximately 1/6 of that for Gd2Zr2O7 prepared using the same sintering process. Furthermore, 7RE2Zr2O7 possessed a high hardness of up to 13.86 GPa, while a low fracture toughness of 1.1 MPa m1/2, which can be mainly attributed to the severe internal stress and defects originated from the fast-sintering process. This work is expected to provide a guidance for the highly efficient and rapid preparation of high-entropy A2B2O7 oxides, especially for those compositions that are difficult to densify.