Negative thermal expansion of (Al1/3Fe1/3Cr1/3)2(Mo1/2W1/2)3O12 (AFCMW) and low thermal expansion of AFCMW-(Co1/2Ni1/2)(Mo1/2W1/2) O4 with high entropy

A2Mo3O12 (A-Al, Fe, Cr) have large negative thermal expansion (NTE) coefficients and structural stability but high phase-transition temperatures (PTTs). Herein, we prepared (Al1/3Fe1/3Cr1/3)2(Mo1/2W1/2)3O12 (AFCMW), and found it to have a low NTE coefficient and a low PTT. Furthermore, combination of AFCMW with (Co1/2Ni1/ 2)(Mo1/2W1/2)O4 (CNMW) afforded an AFCMW-CNMW composite with a low thermal expansion (LTE). We determined that the PTT reductions in A2Mo3O12 are largely due to the high-entropy effect resulting from the introduction of different ions into its A and M sites. Moreover, we found that the low LTE of the AFCMW-CNMW composite is attributable to the opposite thermal expansion behaviours of AFCMW and CNMW. We suggest that the suppressed thermal expansion during the phase transition process of the AFCMW-CNMW composite could be derived from the high-entropy effect resulting from its increased diversity of polyhedra, the influence of Co2+ and Ni2+ dopants, and CNMW-induced lattice distortion.

Automated summary

In this study, researchers successfully prepared AFCMW with low thermal expansion coefficient and low phase-transition temperature, and combined it with CNMW to create an AFCMW-CNMW composite with low thermal expansion. They found that the phase-transition temperature reduction in A2Mo3O12 is mainly attributed to the high-entropy effect resulting from the introduction of different ions. Furthermore, they discovered that the low thermal expansion of the AFCMW-CNMW composite is due to the opposite thermal expansion behaviors of AFCMW and CNMW.