Cation Defect Mediated Phase Transition in Potassium Tungsten Bronze

Abstract

Applying in situ transmission electron microscopy, the phase instability in potassium tungsten bronze (K x WO 3 , 0.18 < x < 0.57) induced by heating was investigated. The atomistic phase transition pathway of monoclinic K 0.20 WO 3 → hexagonal K m WO 3 (0.18 < m < 0.20) → cubic WO 3 induced by cationic defects (K and W vacancies) was directly revealed. Unexpectedly, a K + -rich tetragonal K n WO 3 (0.40 < n < 0.57) phase would nucleate as well, which may result from the blockage of K + diffusion at the grain boundaries. Our results point out the critical role of the cationic defects in mediating the crystal structures in K x WO 3 , which provide reference to rational structural design for extensive hightemperature applications.

Layer-Dependent NO2-Sensing Performance in MoS2 for Room-Temperature Monitoring

“…The atomic structures of materials can be resolved by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). − Figure a represents the experimental and simulated HAADF-STEM images of ML MoS 2 , where chalcogen columns with two S atoms ( Z = 16) appear darker than metallic columns with one Mo atom ( Z = 42). Such a distinction is reflected in the experimental and simulated intensity profiles featured in Figure b, which indicate the hexagonal 2H-phase atomic patterns (Mo–S 2 –Mo).…”

Diverse Defects in Alkali Niobate Thin Films: Understanding at Atomic Scales and Their Implications on Properties

“…[43,44] These large interstices also allow for various cation accommodations as observed in Figure 5b-e, and offer rich ground for ionic diffusion similar to tetragonal tungsten bronzes (TTBs) which show the same atomic arrangements. [46,47,48,94] Taking into account the diverse range of optoelectronic, electrochromic, catalytic, and conductive properties of TTBs, [48][49][50][51] these line defects can be utilized to create engineered materials with nanoscale functionalities for a multitude of applications. Hence, the identification of the novel interstitial pentagonal line defect opens a new avenue for further investigation and engineering of extended 1D defects in ferroelectric KNN films.…”

Na+ Migration Mediated Phase Transitions Induced by Electric Field in the Framework Structured Tungsten Bronze

“…27 However, the latest in situ transmission electron microscopy (TEM) results demonstrate that the TTB structure nucleates based on the hexagonal tungsten bronze (HTB) structure, while the TTB changes into CTB structure at high temperatures. 28 Nevertheless, the transformation mechanisms are still unclear.…”

“…It was reported that the TTB structure could be obtained by rotating four adjacent WO 6 octahedra in the cubic tungsten bronze (CTB) structure by 45° around their centers, and then forming pentagonal channels with the other surrounding octahedra . However, the latest in situ transmission electron microscopy (TEM) results demonstrate that the TTB structure nucleates based on the hexagonal tungsten bronze (HTB) structure, while the TTB changes into CTB structure at high temperatures . Nevertheless, the transformation mechanisms are still unclear.…”

“…The theoretical calculations predict the detailed structural transformation pathways that involve the twist of structural units and reconstruction of the framework structure. This work offers detailed information on the phase stability of Na 0.36 WO 3.14 within the voltage range during the charging/discharging cycles of SIBs, ,, which could also serve as a guidance for probing the phase instability in other framework structure materials and tungsten bronzes, e.g., K x WO 3 , Cs x WO 3 , etc. ,− …”