Diverse Thermal Expansion Behaviors in Ferromagnetic Cr1−δTe with NiAs-Type, Defective Structures

Negative thermal expansion (NTE) and zero thermal expansion (ZTE) properties are of great significance for the long-life stable operation of precision equipment. However, there are still existing challenges in finding new materials that exhibit NTE or ZTE over a wide temperature range. Here, we report negative, zero, and positive thermal expansion in NiAs-type, defective Cr1−δTe, containing three compounds: hexagonal CrTe, monoclinic Cr3Te4, and trigonal Cr5Te8. CrTe shows the NTE behavior from 280 to 340 K with the volume coefficient of thermal expansion αV = −27.6 × 10–6 K–1. Cr3Te4 shows the ZTE behavior over a wide temperature range of 180–320 K (αV = 0.16 × 10–6 K–1). And Cr5Te8 holds the PTE behavior over the whole temperature range (αV = 38.5 × 10–6 K–1). All of the samples show obvious anisotropic thermal expansion on heating. Combined with the magnetic measurements, it can be confirmed that the NTE and ZTE properties in ferromagnetic Cr1−δTe originate from the magnetovolume effect (MVE). Such NiAs-type, defective compounds with similar compositions but different structures provide a new perspective for tuning the NTE properties of materials and searching for new materials with ZTE over a wide temperature range.