Metal oxide semiconductors (MOSs) are attractive candidates as functional parts and connections in nanodevices. Upon spatial dimensionality reduction, the ubiquitous strain encountered in physical reality may result in structural instability and thus degrade the performance of MOS. Hence, the basic insight into the structural evolutions of low-dimensional MOS is a prerequisite for extensive applications, which unfortunately remains largely unexplored. Herein, we review the recent progress regarding the mechanical deformation mechanisms in MOSs, such as CuO and ZnO nanowires (NWs). We report the phase transformation of CuO NWs resulting from oxygen vacancy migration under compressive stress and the tensile strain-induced phase transition in ZnO NWs. Moreover, the influence of electron beam irradiation on interpreting the mechanical behaviors is discussed.
Framework
structured tungsten bronzes serve as promising candidates
for electrode materials in sodium-ion batteries (SIBs). However, the
tungsten bronze framework structure changes drastically as mediated
by the sodium ion concentration at high temperatures. While the three-dimensional
ion channels facilitate fast ion storage and transport capabilities,
the structural instability induced by Na+ migration is
a big concern regarding the battery performance and safety, which
unfortunately remains elusive. Here, we show the real-time experimental
evidence of the phase transitions in framework structured Na0.36WO3.14 (triclinic phase) by applying different external
voltages. The Na+-rich (Na0.48WO3, tetragonal phase) or -deficient (Na
x
WO3, x < 0.36, hexagonal phase) phase
nucleates under the positive or negative bias, respectively. Combined
with the theoretical calculations, the atomistic phase transition
mechanisms associated with the Na+ migration are directly
uncovered. Our work sheds light on the phase instability in sodium
tungsten bronzes and paves the way for designing advanced SIBs with
high-stability.
Due to the violation of the valence
electron counting (VEC) rule
as well as the excess Sn introduced in the synthesis, cubic In5S4 has been recognized as In4SnS4. However, recent reports have indicated the presence of In5S4 via X-ray diffraction characterization, and
no extra Sn participates in the synthesis. Through density functional
theory calculation, we find that In5S4 obeys
the VEC rule by partly forming S1– in the S–S
dimer configuration. Even though In5S4 is found
to be theoretically unstable against InS and In secondary phases,
the phonon dispersion and ab initio molecular dynamics simulation
show that In5S4 exhibits dynamic stability,
indicating that the nonequilibrium conditions (high pressure and high
temperature) could help stabilize In5S4. Benefiting
from low-lying p states of S–S dimer as well
as s and p states from [In5]7+ tetrahedron in conduction bands, In5S4 exhibits a small direct band gap of 1.33 eV and strong visible
light absorption. Our results provide a new perspective of charge
balance on the stability issue of In5S4 and
prove that it has great potential to be applied in the ultimate optoelectrical
application.
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