11 research outputs found
Analyses of Microstructure and Oxygen Content Effects on Thermal Conductivity of AlN Ceramics by Using Slack’s Plot
Analysis of CO<sub>2</sub> absorption reaction of Li<sub>4</sub>SiO<sub>4</sub> on the basis of madelung potential of Li site in crystal structure
Observation of Anion Order in Pb<sub>2</sub>Ti<sub>4</sub>O<sub>9</sub>F<sub>2</sub>
The
observation of anion order is indispensable for the investigation
of oxyfluorides. However, the negligible contrast between O<sup>2–</sup> and F<sup>–</sup> in both X-ray and neutron diffraction obscures
the distinct anion sites for Rietveld refinement. Therefore, the difference
in the chemical bonding of M–O<sup>2–</sup> and M–F<sup>–</sup> is the key to determining anion order. In this study,
bond-valence-sum calculations and determination of the electron density
distribution by the maximum entropy method illustrated anion order
in the newly synthesized oxyfluoride Pb<sub>2</sub>Ti<sub>4</sub>O<sub>9</sub>F<sub>2</sub>. These results demonstrate a promising method
to determine anion order in mixed anion systems
Incorporation of sulfur ions into La2−xSrxCuO4 superconducting cuprate
The superconductivity of La2CuO4-based materials is known to be achievable by doping holes in Cu ions. In this study, the hole content was tuned by mixing anion sites with oxygen and sulfur. The substitution of La1.7Sr0.3CuO4 with sulfur led to the recovery of superconductivity from overdoped regions, a result indicative of decreased hole content. Precise structural analysis revealed that the majority of sulfur is incorporated into impurities in the SrSO4 phase, which decreases the hole content of Cu ions via a decrease in the Sr content; however, the superconductivity cannot be interpreted by this mechanism alone. Supporting evidence for the incorporation of sulfur into the La1.7Sr0.3CuO4Sx phase was obtained by an investigation of the composition dependence of the lattice parameters and X-ray photoelectron spectroscopy. Substitution of oxygen with sulfur, which served to decrease the hole content, as a means of recovering superconductivity was shown to act
Li₁₁Nd₁₈Fe₄O\u3csub\u3e39-δ\u3c/sub\u3e Revisited
The structure proposed for Li11Nd18Fe 4O39-δ (Chen et al. Inorg. Chem. 2012, 51, 8073) on the basis of diffraction and Mössbauer spectral data is compared to that determined previously for Nd18Li8Fe5O 39 (Dutton et al. Inorg. Chem.200847, 11212) using the same techniques. The Mössbauer spectrum reported by Chen et al. has been reinterpreted. The newly refined spectral parameters differ significantly from the published values but are similar to those reported for Nd 18Li8Fe5O39. The relative areas of the three components indicate that iron cations occupy the 2a, 8e, and 16i sites in space group Pm3Ì...n, in disagreement with the model determined from neutron diffraction by Chen et al. in which only the 2a and 8e sites are so occupied. The relationship between Li11Nd18Fe 4O39-δ and Nd18Li8Fe 5O39 is discussed, and it is proposed that the sample prepared by Dutton et al. is a kinetic product whereas the sample prepared by Chen et al. is the thermodynamically preferred product
Reductive Formation of a Vanadium(IV/V) Oxide Cluster Complex [V<sub>8</sub>O<sub>19</sub>(4,4′‑<sup><i>t</i></sup>Bubpy)<sub>3</sub>] Having a <i>C</i><sub>3</sub>‑Symmetric Propeller-Shaped Nonionic V<sub>8</sub>O<sub>19</sub> Core
A novel <i>C</i><sub>3</sub>-symmetric propeller-shaped vanadium(IV/V) oxide cluster
complex, [V<sub>8</sub>O<sub>19</sub>(4,4′-<sup><i>t</i></sup>Bubpy)<sub>3</sub>] (<b>V</b><sub><b>8</b></sub><b>′</b>), has been synthesized from the reaction of
the windmill-shaped vanadium(V) oxide cluster complex [V<sub>8</sub>O<sub>20</sub>(4,4′-<sup><i>t</i></sup>Bubpy)<sub>4</sub>] (<b>V</b><sub><b>8</b></sub>) with PPh<sub>3</sub> under N<sub>2</sub>, whereas refluxing <b>V</b><sub><b>8</b></sub> in methanol or ethanol under N<sub>2</sub> provides
tetranuclear oxido(alkoxido)vanadium(IV/V) complexes [V<sub>4</sub>O<sub>6</sub>(OR)<sub>6</sub>(4,4′-<sup><i>t</i></sup>Bubpy)<sub>2</sub>] [R = Me (<b>V</b><sub><b>4</b></sub><b>′-Me</b>) and Et (<b>V</b><sub><b>4</b></sub><b>′-Et</b>)]. The mixed-valent vanadium(IV/V)
clusters <b>V</b><sub><b>8</b></sub><b>′</b> and <b>V</b><sub><b>4</b></sub><b>′</b> are converted back to <b>V</b><sub><b>8</b></sub> under
O<sub>2</sub>. Interconversions of <b>V</b><sub><b>4</b></sub><b>′</b> and the oxido(alkoxido)vanadium(V) complexes
[V<sub>4</sub>O<sub>8</sub>(OMe)<sub>4</sub>(4,4′-<sup><i>t</i></sup>Bubpy)<sub>2</sub>] (<b>V</b><sub><b>4</b></sub>) and [V<sub>7</sub>O<sub>17</sub>(OEt)(4,4′-<sup><i>t</i></sup>Bubpy)<sub>3</sub>] (<b>V</b><sub><b>7</b></sub><b>-Et</b>) are also presented
Carta de Pere Pascual al prof. Ángel Morales (Universidad de Zaragoza) informant de peticions rebudes dels Drs. B. Geyer i E. M. Jigenfritz per a les Actes del IV Seminario del GIFT
Polycrystalline samples of Ln18Li8Rh 5?xFexO39 (Ln = La, Nd; 0.5 ≤ x ≤ 5) have been synthesized by a solid-state method and studied by a combination of dc and ac magnetometry, neutron diffraction, and Mössbauer spectroscopy. All compositions adopt a cubic structure (space group Pm3n, a0 ~ 12 Å) based on intersecting \u3c111\u3e chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Ln?O framework. At low values of x, iron preferentially occupies the smaller (2a) of the two distinct octahedral sites as low-spin Fe(IV). The Rh(III) on the larger (8e) octahedral site is replaced by high-spin Fe(III). Nd-containing compositions having x \u3e 1 show spin-glass-like behavior below ~5 K. La-containing compositions having x \u3e 1 show evidence of a magnetic transition at ~8 K, but the nature of the transition is unclear. This contrasting behavior demonstrates that, although the structural chemistry of the two systems is essentially the same, the magnetic character of the Ln cations plays an important role in determining the properties of these compounds
Suppressed Activation Energy for Interfacial Charge Transfer of a Prussian Blue Analog Thin Film Electrode with Hydrated Ions (Li<sup>+</sup>, Na<sup>+</sup>, and Mg<sup>2+</sup>)
Interfacial charge transfer is one
of the most important fundamental
steps in the charge and discharge processes of intercalation compounds
for rechargeable batteries. In this study, temperature-dependent electrochemical
impedance spectroscopy was carried out to clarify the origin of the
high power output of aqueous batteries with Prussian blue analog electrodes.
The activation energy for the interfacial charge transfer, <i>E</i><sub>a</sub>, was estimated from the temperature dependence
of the interfacial charge transfer resistance. The <i>E</i><sub>a</sub> values with Li<sup>+</sup> and Na<sup>+</sup> aqueous
electrolytes were considerably smaller than those with organic electrolytes.
The small <i>E</i><sub>a</sub> values with aqueous electrolytes
could result from the fact that the Coulombic repulsion at the interface
is largely suppressed by the screening effect of hydration
Electrospinning Synthesis of Wire-Structured LiCoO<sub>2</sub> for Electrode Materials of High-Power Li-Ion Batteries
An application of the Li-ion batteries to advanced transportation
systems essentially requires the enhancement of the rate capability;
thus, the fabrication of nanostructured cathode materials with the
large surface area and short Li-ion diffusion length is particularly
important. In this study, an electrospinning method was adopted for
the synthesis of wire-structured LiCoO<sub>2</sub>. The diameter of
the as-spun fiber obtained from the precursor solution with multiwalled
carbon nanotubes (vapor-grown carbon fiber, VGCF) was thinner than
that of as-spun fiber obtained from the solution without VGCF. After
the heat treatment, wire-structured LiCoO<sub>2</sub> was successfully
obtained regardless of the existence of dispersed VGCF in the precursor
solution, although the particle size of LiCoO<sub>2</sub> fabricated
with VGCF was smaller than that of LiCoO<sub>2</sub> fabricated without
VGCF. The charge/discharge and rate-capability experiments revealed
that both resulting materials show the reversible Li-ion insertion/extraction
reaction. However, due to the existence of a small irreversible capacity
at the initial cycles, the interfacial resistance increases, resulting
in the poor cyclability and lower charge/discharge rate capability,
especially for nanowire LiCoO<sub>2</sub> fabricated with VGCF
Precise Electrochemical Control of Ferromagnetism in a Cyanide-Bridged Bimetallic Coordination Polymer
Magnetic coordination polymers can exhibit controllable
magnetism
by introducing responsiveness to external stimuli. This report describes
the precise control of magnetism of a cyanide-bridged bimetallic coordination
polymer (Prussian blue analogue: PBA) through use of an electrochemical
quantitative Li ion titration technique, i.e., the galvanostatic intermittent
titration technique (GITT). K<sub>0.2</sub>Ni[Fe(CN)<sub>6</sub>]<sub>0.7</sub>·4.7H<sub>2</sub>O (NiFe-PBA) shows Li ion insertion/extraction
reversibly accompanied with reversible Fe<sup>3+</sup>/Fe<sup>2+</sup> reduction/oxidation. When Li ion is inserted quantitatively into
NiFe-PBA, the ferromagnetic transition temperature <i>T</i><sub>C</sub> gradually decreases due to reduction of paramagnetic
Fe<sup>3+</sup> to diamagnetic Fe<sup>2+</sup>, and the ferromagnetic
transition is completely suppressed for Li<sub>0.6</sub>(NiFe-PBA).
On the other hand, <i>T</i><sub>C</sub> increases continuously
as Li ion is extracted due to oxidation of diamagnetic Fe<sup>2+</sup> to paramagnetic Fe<sup>3+</sup>, and the ferromagnetic transition
is nearly recovered for Li<sub>0</sub>(NiFe-PBA). Furthermore, the
plots of <i>T</i><sub>C</sub> as a function of the amount
of inserted/extracted Li ion <i>x</i> are well consistent
with the theoretical values calculated by the molecular-field approximation