4 research outputs found
Pressure-Induced Ferroelastic Transition Drives a Large Shape Change in a Ni(II) Complex Single Crystal
Crystals with significant length
reduction at an accessible low
pressure are highly desirable for piezo-responsive devices. Here,
we show a molecular crystal [Ni(en)3](ox) (en = ethylenediamine
and ox = oxalate anion) that exhibits an abrupt shape change with
a contraction rate of ∼4.7% along its c axis
near the phase transition pressure of ∼0.2 GPa. High-pressure
single-crystal X-ray diffraction and Raman spectroscopy measurements
reveal that this material undergoes a first-order ferroelastic transition
from high-symmetry trigonal P3̀…1c to low-symmetry monoclinic P21/n at ∼0.2 GPa. The oxalate anions serve as unique
components, and their disorder–order transformation and rotation
of 90° through cooperative intermolecular hydrogen bonding triggered
unconventional anisotropic microsize contraction under compression,
which can be appreciated visually. Such a prominent directional deformation
at a low pressure driven by molecular motors of oxalate anions provides
insights for the design of novel molecular crystal-based piezo-responsive
switches and actuators in deep-sea environments
Pressure-Induced Ferroelastic Transition Drives a Large Shape Change in a Ni(II) Complex Single Crystal
Crystals with significant length
reduction at an accessible low
pressure are highly desirable for piezo-responsive devices. Here,
we show a molecular crystal [Ni(en)3](ox) (en = ethylenediamine
and ox = oxalate anion) that exhibits an abrupt shape change with
a contraction rate of ∼4.7% along its c axis
near the phase transition pressure of ∼0.2 GPa. High-pressure
single-crystal X-ray diffraction and Raman spectroscopy measurements
reveal that this material undergoes a first-order ferroelastic transition
from high-symmetry trigonal P3̀…1c to low-symmetry monoclinic P21/n at ∼0.2 GPa. The oxalate anions serve as unique
components, and their disorder–order transformation and rotation
of 90° through cooperative intermolecular hydrogen bonding triggered
unconventional anisotropic microsize contraction under compression,
which can be appreciated visually. Such a prominent directional deformation
at a low pressure driven by molecular motors of oxalate anions provides
insights for the design of novel molecular crystal-based piezo-responsive
switches and actuators in deep-sea environments
Pressure-Induced Ferroelastic Transition Drives a Large Shape Change in a Ni(II) Complex Single Crystal
Crystals with significant length
reduction at an accessible low
pressure are highly desirable for piezo-responsive devices. Here,
we show a molecular crystal [Ni(en)3](ox) (en = ethylenediamine
and ox = oxalate anion) that exhibits an abrupt shape change with
a contraction rate of ∼4.7% along its c axis
near the phase transition pressure of ∼0.2 GPa. High-pressure
single-crystal X-ray diffraction and Raman spectroscopy measurements
reveal that this material undergoes a first-order ferroelastic transition
from high-symmetry trigonal P3̀…1c to low-symmetry monoclinic P21/n at ∼0.2 GPa. The oxalate anions serve as unique
components, and their disorder–order transformation and rotation
of 90° through cooperative intermolecular hydrogen bonding triggered
unconventional anisotropic microsize contraction under compression,
which can be appreciated visually. Such a prominent directional deformation
at a low pressure driven by molecular motors of oxalate anions provides
insights for the design of novel molecular crystal-based piezo-responsive
switches and actuators in deep-sea environments
Correlated High-Pressure Phase Sequence of VO<sub>2</sub> under Strong Compression
Understanding
how the structures of a crystal behave under compression
is a fundamental issue both for condensed matter physics and for geoscience.
Traditional description of a crystal as the stacking of a unit cell
with special symmetry has gained much success on the analysis of physical
properties. Unfortunately, it is hard to reveal the relationship between
the compressed phases. Taking the family of metal dioxides (MO<sub>2</sub>) as an example, the structural evolution, subject to fixed
chemical formula and highly confined space, often appears as a set
of random and uncorrelated events. Here we provide an alternative
way to treat the crystal as the stacking of the coordination polyhedron
and then discover a unified structure transition pattern, in our case
VO<sub>2</sub>. X-ray diffraction (XRD) experiments and first-principles
calculations show that the coordination increase happens only at one
apex of the V-centered octahedron in an orderly fashion, leaving the
base plane and the other apex topologically intact. The polyhedron
evolves toward increasing their sharing, indicating a general rule
for the chemical bonds of MO<sub>2</sub> to give away the ionicity
in exchange for covalency under pressure