Ultrafast high-temperature sintering of high-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Hf2O7 ceramics with fluorite structure

High-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Hf2O7 (5LaH) hafnate was designed and successfully prepared by the emerging ultrafast high-temperature sintering (UHS) in less than six minutes. The prepared 5LaH has an ultra-high hardness (1089 HV0.3) and an extremely low thermal conductivity of 0.93 W/(m·k), which are mainly attributed to the severe lattice distortion inside the high-entropy material. Furthermore, the grain size only grows at a rate of 0.09 μm/h at 1500 °C, which shows hugely sluggish grain growth characteristics. After annealing at 1300 °C for 30 h, the 5LaH maintains the initial fluorite structure, which exhibits excellent high-temperature phase stability owing to the higher configurational entropy that causes a decrease in the Gibbs free energy of the high-entropy material system. Therefore, 5LaH has excellent potential as the next-generation thermal barrier coating material, and the UHS has excellent prospects in developing and rapidly synthesizing new ceramic materials.