Pressure-Induced Structural Phase Transition, Anomalous Insulator-to-Metal Transition, and n-p Conduction-Type Switching in Defective, NiAs-Type CrTe.

CrTe, as a unique series of defective compounds with a NiAs-type structure and periodic metal vacancies, has attracted intensive research interest because of its diversity in structure and property dependent on the tunable stoichiometric ratio. Another feature of these compounds is their ability to switch between NiAs- and MnP-type structures, in which there often exist composition-, temperature-, or pressure-induced phase transitions accompanied by intriguing physical property switching. Herein, we report the syntheses of a series of CrTe compounds with similar compositions but distinct crystal structures, their phase transitions, anomalous transport, and photoelectric conduction behaviors under high pressure (HP). For the three CrTe compounds with δ = 0, 0.25, 0.375, CrTe undergoes pressure-induced NiAs-to-MnP phase transition at around 15 GPa, while CrTe and CrTe undergo isostructural phase transitions at around 12 and 11 GPa, respectively. Electrical transport measurements indicate anomalous conduction behaviors: CrTe undergoes a semiconductor-to-metal transition at around 24 GPa, while CrTe and CrTe show unexpected metal-semiconductor-metal transitions sequentially upon compression. Besides, CrTe and CrTe exhibit pressure-induced n-p conduction-type switching at around 9 and 3 GPa, respectively, while CrTe shows p-type conductivity in the full pressure range. Local structure analyses based on in situ HP Raman spectra are performed to understand the structure and property evolutions of CrTe under HP. Defective transition-metal chalcogenides with pressure-induced NiAs-to-MnP phase transition and conduction-type conversion provide a potential platform for the rational design of photoelectric conversion devices.