Inhibition of hotspot formation by alumina addition in flash sintering of (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 high-entropy ceramic

Sintering inhomogeneities caused by hotspots are one of the factors hindering the development of flash sintering technology. Herein, to overcome this problem for a high-entropy pyrochlore-structured (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 ) 2 Zr 2 O 7 ceramic (abbreviated as RE 2 Zr 2 O 7 ), we propose a simple strategy, namely, addition of Al 2 O 3 to the ceramic and achieved a significant effect. During flash sintering, rare earth ions in RE 2 Zr 2 O 7 reacted with Al 2 O 3 to form REAlO 3 and RE 2−x Zr 2 O 7–3x/2 , which substantially improved the sintering homogeneity. With an increase in the Al 2 O 3 content, REAlO 3 transformed into REAl 11 O 18 . The crack deflection and bridging effect caused by the formation of these phases and their intrinsic high hardness and high modulus improved the mechanical properties of the composite ceramic. The use of an internal reaction to improve the electrical conductivity of a ceramic body is an economical and effective strategy to prevent hotspot formation during flash sintering.