62 research outputs found
Phase Transition for Zinc Sulfide Nanosheets under High Pressure
This study describes the pressure-induced
behavior of ZnS nanosheets
by synchrotron angle-dispersive X-ray diffraction (ADXD) measurement
up to 32.7 GPa. ZnS nanosheets transform from zinc blende structure
to rock salt phase at 13.1 GPa and subsequently to a <i>Cmcm</i> structure at 20.3 GPa. The transition to the <i>Cmcm</i> structure is irreversible for ZnS nanomaterials at a much lower
critical pressure than required for ZnS bulk materials. The special
morphology of ZnS nanosheets plays a crucial role in the transition
to <i>Cmcm</i> structures at comparatively low pressure.
Continuous changes in lattice volume in the absence of volume collapse
are observed after the transition from rock salt to the <i>Cmcm</i> structure occurs
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Morphology-Tuned Phase Transitions of Horseshoe Shaped BaTiO<sub>3</sub> Nanomaterials under High Pressure
Exploring new physical
properties of nanomaterials with special
morphology have been important topics in nanoscience and nanotechnology.
Here we report a morphology-tuned structural phase transition under
high pressure in the horseshoe shaped BaTiO<sub>3</sub> nanomaterials
with an average diameter of 26 ± 4 nm. A direct structural phase
transition from the tetragonal to the cubic phase without local rhombohedral
distortion was observed at about 7.7 GPa by in situ high-pressure
X-ray diffraction and Raman spectroscopy, which is clearly different
from the phase transition processes of the BaTiO<sub>3</sub> bulks
and nanoparticles. Additionally, bulk modulus of the tetragonal and
cubic phases were determined to be 125.0 and 211.7 GPa, respectively,
obviously smaller than the estimated values for BaTiO<sub>3</sub> nanoparticles
with the same grain size. Further analysis shows that the unique phase
transition process and the enhanced structural stability of the tetragonal
horseshoe shaped BaTiO<sub>3</sub> nanomaterials, may be attributed
to the similar axes compressibility. Comparing with the high-pressure
study on BaTiO<sub>3</sub> nanoparticles, this study suggests that
the morphology plays an important role in the pressure-induced phase
transition of BaTiO<sub>3</sub> nanomaterials
Luminescence Properties of Compressed Tetraphenylethene: The Role of Intermolecular Interactions
Mechanochromic materials with aggregation-induced
enhanced emission
(AIEE) characteristic have been intensively expanded in the past few
years. In general, intermolecular interactions invariably alter photophysical
processes, while their role in the luminescence properties of these
AIEE-active molecules is difficult to fully recognize because the
pressurized samples possess amorphous nature in many cases. We now
report the high-pressure studies on a prototype AIEE-active molecule,
tetraphenylethene, using diamond anvil cell technique with associated
spectroscopic measurements. An unusual pressure-dependent color, intensity,
and lifetime change in tetraphenylethene has been detected by steady-state
photoluminescence and time-resolved emission decay measurements. The
flexible role of the aromatic C–H···π
and C–H···C contacts in structural recovery,
conformational modification, and emission efficiency modulation upon
compression is demonstrated through structure and infrared analysis
Exploration of the Hydrogen-Bonded Energetic Material Carbohydrazide at High Pressures
We
have reported the high-pressure behavior of hydrogen-bonded
energetic material carbohydrazide (CON<sub>4</sub>H<sub>6</sub>, CHZ)
via <i>in situ</i> Raman spectroscopy and angle-dispersive
X-ray diffraction (ADXRD) in a diamond anvil cell with ∼15
GPa at room temperature. Significant changes in Raman spectra provide
evidence for a pressure-induced structural phase transition in the
range of ∼8 to 10.5 GPa. ADXRD experiments confirm this phase
transition by symmetry transformation from <i>P</i>2<sub>1</sub>/<i>n</i> to a possible space group <i>P</i>1̅, which exhibits ∼23.1% higher density at 10.1 GPa
compared to phase <i>P</i>2<sub>1</sub>/<i>n</i> at ambient pressure. Moreover, the observed transition is completely
reversible when the pressure is totally released. On the basis of
the decreased number of hydrogen bonds, the shortened hydrogen bond
lengths, and the variations in the NH and NH<sub>2</sub> stretching
Raman peaks in the high-pressure phase, we propose that this phase
transition is caused by the rearrangement of the hydrogen-bonded networks
Pressure-Induced Phase Transition in N–H···O Hydrogen-Bonded Molecular Crystal Biurea: Combined Raman Scattering and X‑ray Diffraction Study
The response of biurea to high pressures
is investigated by <i>in situ</i> Raman spectroscopy and
angle-dispersive X-ray diffraction (ADXRD) in a diamond anvil cell
up to ∼5 GPa. Raman scattering measurements indicate a phase
transition occurring over the pressure range of 0.6–1.5 GPa.
Phase transition is confirmed by changes in the ADXRD spectra with
symmetry transformation from <i>C</i>2/<i>c</i> to a possible space group <i>P</i>2/<i>n</i>. Upon total release of pressure, the diffraction spectrum returns
to its initial state, which implies that the transition observed is
reversible. We discuss variations in the Raman spectra, including
splitting of modes, appearance of new modes, and abrupt changes in
the slope of the frequency shift curves at several pressures. We propose
that the phase transition observed in this study is attributed to
rearrangement of the hydrogen-bonded networks
<i>Gauche</i>–<i>trans</i> Conformational Equilibrium of Succinonitrile under High Pressure
Organic chain molecules have considerable
importance because of
their conformational stability, which is fundamental to their chemical
stability. The phase behaviors and conformational equilibrium of simple
hydrocarbons and their derivatives under extreme conditions are of
interest to research because of their applications. In situ high-pressure
Raman spectroscopy studies on succinonitrile up to 24 GPa at ambient
temperature have been conducted to investigate its structural properties
and conformational equilibria. Succinonitrile has undergone a plastic-to-crystal
phase transition around 0.7 GPa. A simultaneous conversion of <i>gauche</i> to <i>trans</i> conformation has been observed.
A crystal-to-crystal phase transition has subsequently occurred around
2.9 GPa. The second high-pressure phase has remained stable up to
24 GPa. These two crystal structural transitions have also been confirmed
by in situ high-pressure angle-dispersive X-ray diffraction experiments.
Compared with the reported low-temperature phase, the new phases under
high pressure have different molecular conformations and higher densities,
which can provide better understanding of the paths of conformational
transitions under different extreme conditions
Genome-Scale Transcriptome Analysis of the Alpine “Glasshouse” Plant <i>Rheum nobile</i> (Polygonaceae) with Special Translucent Bracts
<div><p>Background</p><p><i>Rheum nobile</i> is an alpine plant with translucent bracts concealing the inflorescence which produce a “glasshouse” effect promoting the development of fertile pollen grains in such conditions. The current understanding of the adaptation of such bracts to alpine environments mainly focuses on the phenotypic and physiological changes while the genetic basis is very limited. By sequencing the upper bract and the lower rosulate leaf from the same <i>R. nobile</i> stem, we identified candidate genes that may be involved in alpine adaption of the translucent bract in “glasshouse” plants and illustrated the changes in gene expression underlying the adaptive and complex evolution of the bracts phenotype.</p><p>Results</p><p>A total of 174.2 million paired-end reads from each transcriptome were assembled into 25,249 unigenes. By comparing the gene expression profiles, we identified 1,063 and 786 genes up-regulated respectively in the upper bract and the lower leaf. Functional enrichment analyses of these genes recovered a number of differential important pathways, including flavonoid biosynthesis, mismatch repair and photosynthesis related pathways. These pathways are mainly involved in three types of functions: 9 genes in the UV protective process, 9 mismatch repair related genes and 88 genes associated with photosynthesis.</p><p>Conclusions</p><p>This study provides the first comprehensive dataset characterizing <i>Rheum nobile</i> gene expression at the transcriptomic scale, and provides novel insights into the gene expression profiles associated with the adaptation of the “glasshouse” plant bracts. The dataset will be served as a public genetic resources for further functional and evolutionary studies of “glasshouse” plants.</p></div
New Assembly of Acetamidinium Nitrate Modulated by High Pressure
High pressure is an essential thermodynamic
parameter in exploring
the performance of condensed energetic materials. Combination of high-pressure
techniques and supramolecular chemistry opens a new avenue for synthesis
of high energy density materials. Herein, we fabricate a new high-pressure-assisted
assembly of energetic material acetamidinium nitrate (C<sub>2</sub>N<sub>2</sub>H<sub>7</sub><sup>+</sup>·NO<sub>3</sub><sup>–</sup>, AN) with <i>P</i>-1 symmetry after a 0–12 GPa–0
treatment at room temperature, which exhibits a density that is 9.8%
higher than that of the initial <i>P</i>2<sub>1</sub>/<i>m</i> phase. Evolution of intermolecular lattice modes in Raman
spectra and synchrotron X-ray diffraction (XRD) patterns provide strong
evidence for this transition in the 1.3–3.4 GPa range. The
mechanism involves relative motions between ionic pairs in the hydrogen-bonded
array and distortions of building blocks
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