Evolution of Temperature-Induced Isostructural Phase Transition in a Newly Grown Layered FeTe₂ Single Crystal

Layered FeTe2 (l-FeTe2) was supposed to be one of the most important compounds in the family of two-dimensional transition-metal dichalcogenides (2D TMDs) owing to the importance of an iron element and its predicted novel physical phenomena. However, 2D layered FeTe2 is rarely reported because of its tendency to be stabilized in three-dimensional marcasite phase structures. Here, we report, for the first time, a pure and large-size l-FeTe2 single crystal synthesized successfully in a P3̅m1 hexagonal space group using a solid-state reaction method. Thermoanalysis and X-ray diffraction (XRD) data after annealing at different temperatures indicate that l-FeTe2 is a metastable material. The results of electrical transport, magnetization, and in situ low-temperature XRD measurements confirm that l-FeTe2 undergoes a first-order isostructural phase transition from 120 to 150 K, and we established a detailed correlation among these properties of l-FeTe2. l-FeTe2 transforms from an insulating to metallic state at 120 K where the phase transition completes. In addition, the Shubnikov–de Haas (SdH) oscillation phenomenon is observed under a high magnetic field at 4 K.