Diverse Thermal Expansion Behaviors in Ferromagnetic Cr 1-δ Te 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-δ Te, containing three compounds: hexagonal CrTe, monoclinic Cr 3 Te 4 , and trigonal Cr 5 Te 8 . 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 . Cr 3 Te 4 shows the ZTE behavior over a wide temperature range of 180-320 K (α V = 0.16 × 10 -6 K -1 ). And Cr 5 Te 8 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-δ Te 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.