Pressure-Induced Reversible Phase Transformation in Nanostructured Bi₂Te₃ with Reduced Transition Pressure

Abstract

High-pressure research on nanostructured materials has been of considerable interest owing to the quantum confinement effect and intrinsic defects in the nanocrystals. Here, we report a pressure-induced reversible structural phase transition in nanostructured Bi 2 Te 3 hierarchical architectures (HAs) that were prepared via a facile solution-phase method. Therein, distinct phases I−IV by respectively adopting crystal structures of rhombohedral (I), monoclinic (II, III), and cubic (IV) were experimentally identified with increasing pressure up to 20.2 GPa in a diamond anvil cell (DAC). It is worthwhile to notice that nanostructured Bi 2 Te 3 HAs ultimately evolved into a fascinating Bi−Te substitutional nonmetallic alloy at pressure even as low as 15.0 GPa, approximately 10 GPa lower than that of the corresponding bulk counterpart. The synergistic effect involving large volume collapse and the unique one-dimensional nanostructures with intrinsic antisite defects was proposed to be responsible for the reduction of transition pressure that is contrary to the general model for most nanomaterials. Our findings may pave a potential pathway for developing future multifunctional nanoalloys that are composed of nonmetallic elements. ■ INTRODUCTIONAlloys have been anticipated to be widely utilized in engineering and industry owing to their extraordinary properties, such as much stronger hardness and toughness, depressed electric and thermal conductivity, and lower melting point than each separated constituent alone. 1,2 These unique characteristics of an alloy are able to render people manufacture the target material with desired properties for a given practical application. However, most alloys are composed of metal elements; thus, searching for other alternatives of new and enhanced functional alloys as well as their prepared strategy is of great interest and remains challenging.Applications of high pressure have proven to be a powerful tool in tailoring the material's properties, especially since the development in the 1950s of the diamond anvil cell (DAC), which made it possible to generate pressures even above 100 GPa. 3−6 Intriguingly, nanomaterials subjected to high-pressure conditions can greatly increase opportunities of exploring novel physical phenomena because of the quantum confinement effect and intrinsic defects yielded by the stark decrease in size. 7−13 In this respect, Tolbert and Alivisatos, as pioneers in 1994, systematically investigated in situ high-pressure structural phase transition of monodispersed CdSe nanoparticles by applying DAC apparatus. 14 Inspired by the size effect of nanomaterials, Wang et al. have recently reported a critical sizedependent amorphization of nanoscale Y 2 O 3 particles at high pressure. 15 Meanwhile, Fan's group further developed high pressure as a potential means for morphology regulation of noble metal nanocrystals. 16−18 Our group has also made a progress in high-pressure nanomaterial studies over the different stabilities and phase transition routines for nanosized YP...

Strategies and challenges of high-pressure methods applied to thermoelectric materials

“…1), and near 6-7 GPa or somewhat above they all undergo a phase transition to the monoclinic C2/m lattice. 30,53,[75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91] As shown by studies on high-quality single crystals of Bi 2 Te 3 , the pressure behavior of its Seebeck coefficient depends strongly on carrier concentration. 51,53 For example, in undoped p-type crystals with carrier concentrations of about 10 17 cm −3 and below, an applied pressure of 2-4 GPa induces a double p-n-p sign inversion [ p-Bi 2 Te 3 (1) in Fig.…”

“…4(a)], an n-p sign inversion can be observed just before the phase transition to the C2/m lattice near 6-7 GPa. [75][76][77][78][79][80][81][82][83][84][85] These anomalies and the n-p sign inversions can be linked to particular changes in band structure and to redistribution of charge carriers between different bands. 97,98 For polycrystalline samples of n-Bi 2 Te 3 , p-BiSbTe 3 , and p-Sb 2 Te 3 , the thermopower curves do not exhibit any particular FIG.…”

High-Pressure Phase Transitions of Morphologically Distinct Zn2SnO4 Nanostructures

“…23−31 The thermodynamics of phase transformations and relative stabilities of the phases have also been noted in several studies. 24−26,30−33 Although there are conflicting trends in the reported transition pressures relating to the Hall–Petch effect that is found as bulk materials are reduced to smaller crystallites, a significant influence from nanosized particles or grains has been commonly suggested as the cause for the dissimilar types of nucleation, growth dynamics, phase transition pathways, and even sequences of the phase transitions or amorphizations of semiconducting materials under high pressure. 31,32,34,35 A specific size, at which the typical nanoscale effects start to occur in materials, has also been defined as their respective “critical size” in several cases.…”

“…27,32,34 The contributions of the nanoscale-induced differences in the surface energies of the relevant phases mainly account for the stabilities of the corresponding structures. 24,33 In this context, the impacts of various microstructural features, for instance, the distinct shape or morphology, dimension, and homogeneity, of the materials are often found to coincide with the size effects of the nanocrystals in many studies. 9,14,33,36−39 The microstructure-induced strains appearing at the contact points of the grains of the materials may cause significant structural distortions, which also contribute to the transition pressure and phase stability.…”

2D Materials Based on Main Group Element Compounds: Phases, Synthesis, Characterization, and Applications

“…In a pressure‐induced reversible process, many distinct structural phases such as rhombohedral (I), monoclinic (II, III), and cubic (IV) were observed in nanostructured Bi 2 Te 3 . [ 266 ] A facile solution‐phase method was observed to be effective in synthesizing the nanostructure of Bi 2 Te 3 . Pressure‐induced phase transformations from rhombohedral (I) through monoclinic (II, III) up to cubic (IV) was observed after the pressure was increased to 20.2 GPa.…”