High‐Entropy Anti‐Perovskites with Enhanced Negative Thermal Expansion Behavior

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. In this paper, the unique sluggish characteristics and extended optimization space in empirically screened high‐entropy anti‐perovskite (HEAP) are utilized to broaden the NTE temperature range. Typically, the NTE temperature range in Mn3Cu0.2Zn0.2Ga0.2Ge0.2Mn0.2N is broadened to ΔT = 235 K (5 K ≤ T ≤ 240 K), which is two or three times wider than that of traditional low‐entropy doping systems. The neutron diffraction analysis reveals a unique sluggish characteristic in magnetic phase transition which survives in an ultra‐wide temperature range of 5 K ≤ T ≤ 350 K (ΔT = 345 K). The sluggish characteristic is 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. The demonstration provides a unique paradigm for broadening the temperature range of NTE materials through entropy engineering. The unique sluggish characteristics and extended optimization space in high‐entropy anti‐perovskite (HEAP) are utilized to broaden the NTE temperature range. The phase separation with an ultra‐wide temperature range (5 K ≤ T ≤ 350 K) is obtained, which results in a broadened NTE with ΔT = 235 K (5 K ≤ T ≤ 240 K) in typical HEAP Mn3Cu0.2Zn0.2Ga0.2Ge0.2Mn0.2N.