Diverse Thermal Expansion Behaviors in Ferromagnetic Cr_1-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 Cr_1-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 α_V = -27.6 × 10^-6 K^-1. Cr₃Te₄ shows the ZTE behavior over a wide temperature range of 180-320 K (α_V = 0.16 × 10^-6 K^-1). And Cr₅Te₈ holds the PTE behavior over the whole temperature range (α_V = 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 Cr_1-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.