Pressure-Induced Abnormal Electrical Transport Transition from Pure Electronic to Mixed Ionic–Electronic in Multiferroic BiFeO₃ Ceramics

Abstract

Pressure-induced structural changes could induce changes in transport properties and lead to a better understanding of the structure−property relationship. The evolution of the carrier transport properties of BiFeO 3 (BFO) ceramics under a high pressure was investigated through impedance spectroscopy measurements at room temperature combined with first-principles calculations. A pressure-induced abnormal transition from pure electronic to mixed ionic−electronic was found in the BFO ceramics Cmmm and Pnma phases at 7.67 and 11.01 GPa, respectively. The pressure-induced structural phase transition from the R3c phase to Cmmm and then to Pnma was responsible for the change in electrical transport behavior from pure electronic to mixed ionic− electronic conduction, accompanied by a decrease in ionic resistance. The calculations of electronic structures and electron localization function from 1 atm to 40 GPa indicated that the ionic conduction in the Pnma phase resulted from the weakened Coulomb screen of the localized electron background to O 2− between Bi 3+ and O 2− . This work provides a critical insight into the understanding of the relationship between structure and conduction and facilitates the application of ferroelectric materials in photoelectric fields.

Pressure-Modulated Structural and Magnetic Phase Transitions in Two-Dimensional FeTe: Tetragonal and Hexagonal Polymorphs

“…As the key variable in thermodynamics, hydrostatic pressure has been extensively used to nondestructively modulate the lattice structure and further tune the physical properties of functional nanomaterials, 35 such as enhanced superconductivity, 36 abnormal transport behavior, 37 and magnetic phase transitions. 38,39 It has been reported that bulk t-FeTe exhibits rich structural transitions under pressure, 16,40−42 and various anomalies of its electrical resistance appear with increasing pressure, partly due to the strongly entangled structural and electronic transitions that occur.…”

“…As the key variable in thermodynamics, hydrostatic pressure has been extensively used to nondestructively modulate the lattice structure and further tune the physical properties of functional nanomaterials, such as enhanced superconductivity, abnormal transport behavior, and magnetic phase transitions. , It has been reported that bulk t -FeTe exhibits rich structural transitions under pressure, ,− and various anomalies of its electrical resistance appear with increasing pressure, partly due to the strongly entangled structural and electronic transitions that occur. ,− Meanwhile, magnetic studies of t -FeTe under hydrostatic pressure immaturely suggest the magnetic transition from low-pressure AFM order to high-pressure FM order. ,, Moreover, the experimental exploration of the electrical transport, structure, and magnetism of h -FeTe under high pressure is still sparse. 2D crystalline FeTe with tunable phases as well as magnetism is extremely rare in the TMD family. , 2D t -FeTe and h -FeTe nanosheets have an identical chemical composition yet reflect distinct lattice structures and magnetic properties, which provides us a desirable platform to explore their symmetry–magnetism correlation and even to potentially unravel the attractive mechanism in iron-based superconductors.…”