Hybrid metal–organic frameworks (MOFs) demonstrate great promise as ideal electrode materials for energy‐related applications. Herein, a well‐organized interleaved composite of graphene‐like ...nanosheets embedded with MnO2 nanoparticles (MnO2@C‐NS) using a manganese‐based MOF and employed as a promising anode material for Li‐ion hybrid capacitor (LIHC) is engineered. This unique hybrid architecture shows intriguing electrochemical properties including high reversible specific capacity 1054 mAh g−1 (close to the theoretical capacity of MnO2, 1232 mAh g−1) at 0.1 A g−1 with remarkable rate capability and cyclic stability (90% over 1000 cycles). Such a remarkable performance may be assigned to the hierarchical porous ultrathin carbon nanosheets and tightly attached MnO2 nanoparticles, which provide structural stability and low contact resistance during repetitive lithiation/delithiation processes. Moreover, a novel LIHC is assembled using a MnO2@C‐NS anode and MOF derived ultrathin nanoporous carbon nanosheets (derived from other potassium‐based MOFs) cathode materials. The LIHC full‐cell delivers an ultrahigh specific energy of 166 Wh kg−1 at 550 W kg−1 and maintained to 49.2 Wh kg−1 even at high specific power of 3.5 kW kg−1 as well as long cycling stability (91% over 5000 cycles). This work opens new opportunities for designing advanced MOF derived electrodes for next‐generation energy storage devices.
Metal–organic framework derived electrodes for high performance Li‐ion hybrid capacitors: graphene‐like nanosheets wrap a MnO2 anode and nanoporous carbon nanosheet cathode.
The pressure dependence of octahedral distortions in rare-earth (R) orthochromites (RCrO3) has been studied using Raman scattering technique to probe the origin of the structural transition from ...orthorhombic Pnma to rhombohedral R3‾c phase in LaCrO3. The pressure-induced changes in the octahedral tilt modes demonstrate that tilt distortion is suppressed in LaCrO3 and is enhanced in the remaining members of the RCrO3 family. This crossover between the two opposite pressure behaviours occurs at a critical R-ion radius of 1.20 Å. We attempt to establish the relationship between this unusual crossover and compressibility at Cr- and R-sites by probing Raman phonon modes sensitive to the mean bond strength of Cr–O, and R–O, respectively. Finally, we study the bond length splitting of both CrO6 and RO12 polyhedra to ascertain the role of polyhedral self-distortion in determining the pressure dependent structural transition in the orthochromites.
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•Pressure dependence of Raman modes of series of rare-earth chromites (RCrO3) were studied•It was shown that fundamental perovskite distortions enhance with external pressure for all the members of RCrO3 except for LaCrO3•This crossover between the two opposite pressure behaviors occurs at a critical R-ion radius of 1.20 Å.•The role of polyhedral self distortion in determining the pressure evolution of perovskite structure was established.
In search of promising Na
ion conductors, we have detected a superionic phase in a Vantoffite mineral, Na
Co(SO
)
, at 570 °C, thus enhancing the use of minerals to produce futuristic solid state ...electrolytes. Na
Co(SO
)
crystallizes concomitantly to produce di- and tetrahydrate forms from an aqueous solution. Both the crystal forms belong to a triclinic system, space group
1. The mineral transforms to a dehydrated phase as established by
single crystal X-ray diffraction at 217 °C and is shown to be isostructural with its Mn analogue. Even though thermal analysis indicates a single structural phase transition at 450 °C, the features associated with
powder X-ray diffraction as well as
Raman spectroscopy signify a second phase transition ≈540 °C and the behavior of ionic conductivity leads to a superionic phase (σ ≈ 10
S/cm at 570 °C). These observations are significant for the development and understanding of mineral based solid electrolytes.
In two-dimensional (2D) van der Waals (vdW) layered materials the application
of pressure often induces a giant lattice collapse, which can subsequently
drive an associated Mott transition. Here, we ...investigate room-temperature
layer-dependent insulator-metal transition (IMT) and probable spin-crossover
(SCO) in vdW magnet, FePS$_3$, under high-pressure using micro-Raman
scattering. Experimentally obtained spectra, in agreement with the computed
Raman modes, indicate evidence of IMT of FePS$_3$ started with a
thickness-dependent critical pressure ($P_c$) which reduces to 1.5 GPa in
trilayer flakes compared to 10.8 GPa for the bulk counterpart. Using a
phenomenological model, we argue that strong structural anisotropy in few-layer
flakes enhances the in-plane strain under applied pressure and is, therefore,
ultimately responsible for reducing the critical pressure for the IMT with
decreasing layer numbers. Reduction of the critical pressure for phase
transition in vdW magnets to 1-2 GPa marks the possibility of using
intercalated few-layers in the field-effect transistor device architecture, and
thereby, avoiding the conventional use of the diamond anvil cell (DAC).
Temperature evolution of dielectric response, atomic structure, and lattice
dynamics in thin film of sodium niobate in the epitaxial
NaNbO$_3$/SrRuO$_3$/(001)MgO heterostructure is studied by ...dielectric
measurements, x-ray diffraction, and Raman spectroscopy. It is found that at
room temperature NaNbO$_3$ is in ferroelectric state, whereas the
temperature-dependent dielectric constant experiences a broad maximum at 440~K
on cooling and at 500~K on heating and reveals a diffuse phase transition.
Reciprocal space mapping shows the presence of both anti-phase and in-phase
tilting of oxygen octahedra. The temperature dependence of the M-point
reflections suggests reorientation of the in-phase octahedra tilting axis from
being parallel to the substrate at room temperature to perpendicular
orientation at high temperatures. The temperature evolution of the shape of the
Raman spectra reveal the decrease of the number of constituting peaks on
heating. These results are interpreted as indicating a temperature-driven
transition between two different orientations of the bulk ferroelectric Q phase
with respect to the interface, namely between the state with electric
polarization pointing at $\approx45^{\rm o}$ to the normal at room temperature
to the state with polarization parallel to the interface above the transition.
Transitions of this kind can be anticipated from theoretical considerations,
while the experimental evidences of such are yet scarce.
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