Pressure-Induced Structural Phase Transition, Anomalous Insulator-to-Metal Transition, and n–p Conduction-Type Switching in Defective, NiAs-Type Cr_1−δTe

Abstract

Cr1−δTe, 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 Cr1−δTe compounds with similar compositions but distinct crystal structures, their phase transitions, anomalous transport, and photoelectric conduction behaviors under high pressure (HP). For the three Cr1−δTe compounds with δ = 0, 0.25, 0.375, CrTe undergoes pressure-induced NiAs-to-MnP phase transition at around 15 GPa, while Cr3Te4 and Cr5Te8 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 Cr3Te4 and Cr5Te8 show unexpected metal–semiconductor–metal transitions sequentially upon compression. Besides, CrTe and Cr5Te8 exhibit pressure-induced n–p conduction-type switching at around 9 and 3 GPa, respectively, while Cr3Te4 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 Cr1−δTe 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.

Pressure-Induced Reversible and Irreversible Multistate Switching in NiAs-Type Chromium Selenides

“…Localization of carriers can usually lead to an abnormal increase in resistivity under HP. Similar phenomena have been found in Cr 5 Te 8 and MnBi 2 Te 4 . , By the measurements of Hall resistivity, it is observed that the carrier mobility is significantly decreased, which means that the carrier is more localized under HP, thus causing the resistivity increase upon compression. Such intercalated compounds with periodic vacancies seem to be prone to pressure-induced carrier localization.…”

“…This atomic-shift-type (i.e., martensitic) phase transition always leads to abrupt changes in both the electrical and magnetic properties of materials. Previous HP research studies on the Cr–Te system have shown that derivative NiAs-type compounds tend to retain their initial structures under HP but exhibit electronic transitions upon compression . Herein, we focus on the Cr–Se system and present the synthesis and HP studies of two chromium selenides, CrSe and Cr 2 Se 3 .…”

“…NiAs-type compounds tend to undergo structural phase transitions to the MnP-type structure under HP, including MnAs, MnTe, CrTe, and CoSb . This atomic-shift-type (i.e., martensitic) phase transition always leads to abrupt changes in both the electrical and magnetic properties of materials.…”

Photoelectric Properties of Functional Materials under High Pressure

“…This is the result of pressure-induced p-n switching. [80] The photothermal effect is another important mechanism for achieving IPC under high pressures. Generally, the resistance of metallic materials increases linearly with the light-induced increase in temperature, which contributes to IPC.…”

Rewritable Pressure-Driven n–p Conduction Switching in Marcasite-Type CrSb2

“…As an important thermodynamic parameter as temperature, pressure can remarkably modulate the crystal structures and physical properties of materials by changing crystallographic parameters such as bond length and bond angle . Under high pressure (HP), the materials can exhibit a series of binary conversions of physical properties, such as spin-crossover, , piezochromism, , and metal–insulator transition. , In addition, pressure-driven n – p switching has also gradually attracted research interest, which mainly occurs in materials such as elements, , metal oxides, , chalcogenides, − and pnictides. , Among them, there is one class of pressure-driven n – p switching that essentially originates from electronic transitions, typically as the Fermi surface topological changes known as Lifshitz transitions, e.g. , in Bi 2 Te 3 , while the other class is related to pressure-induced structural phase transitions, e.g.…”