  The negative thermal expansion (NTE) materials, which can act as
thermal-expansion compensators to counteract the positive thermal expansion,
have great applications merit in precision engineering. However, the
exploration of NTE behavior with a wide temperature range has reached its upper
ceiling through traditional doping strategies due to composition limitations.
The unique sluggish characteristic in phase transition and extended
optimization space in recent high entropy systems has great potential to
broaden the temperature range in electronic transitions-induced NTE materials.
Mn-based anti-perovskites offer an ideal platform for the exploration of high
entropy NTE material due to their abundant element selection and controllable
NTE performance. In this paper, the high entropy strategy is first introduced
to broaden the NTE temperature range by relaxing the abrupt phase transition in
Mn-based anti-perovskite nitride. We propose an empirical screening method to
synthesize the high-entropy anti-perovskite (HEAP). it is found that magnetic
phase separation from anti-ferromagnetic CII to paramagnetic CI surviving in an
ultra-wide temperature range of 5K<=T<=350K (Delta_T=345K), revealing a unique
sluggish characteristic. Consequently, a remarkable NTE behavior (up to
Delta_T=235K, 5K<=T<=240K) with a coefficient of thermal expansion of
-4.7x10-6/K, has been obtained in HEAP. It is worth noting that the temperature
range is two/three times wider than that of low-entropy systems. The sluggish
characteristic has been further experimentally proved to come from disturbed
phase transition dynamics due to distortion in atomic spacing and chemical
environmental fluctuation observed by the spherical aberration-corrected
electron microscope. Our demonstration provides a unique paradigm for
broadening the temperature range of NTE materials induced by phase transition
through entropy engineering.
