정성훈 교수

Electrical conductivity at the microscopic grain level has been measured in densely sintered polycrystalline samples of and using a four-point microcontact technique. The absolute value of conductivity as well as its spatial variability have been measured, and are consistent with previously reported bulk measurements. The results support the interpretation of the conductivity increase upon doping of as a lattice effect. © 2003 The Electrochemical Society. All rights reserved.

We visualize the antisite exchange defects in LiFePO4 crystals with an ordered olivine structure by using annular dark-field scanning transmission electron microscopy (STEM). A recognizable bright contrast is observed in some of the Li columns of STEM images in a sample annealed at a lower temperature, which directly demonstrates the disordered occupations by Fe atoms. Furthermore, such exchange defects appear to be locally aggregated rather than homogeneously dispersed in the lattice, although

We provide general descriptions regarding the structure–stability correlations of iridium-based complex-oxide catalysts for oxygen evolution reaction in acid media.

Aggregated antisite cations of iron (see picture, red) in the lithium sites of doped lithium iron phosphate (LiFePO4) are arranged preferentially along the b axis. To probe the peculiar array of the defects, Z-contrast STEM with a spherical-aberration correction is utilized. The images obtained using Z-contrast STEM suggest that the distribution of antisite defects in LiFePO4 can be adjusted for improved lithium ion transport. Detailed facts of importance to specialist readers are published as ”

Abstract Due to unparalleled theoretical capacity and operation voltage, metallic Li is considered as the most attractive candidate for lithium‐ion battery anodes. However, Li metal electrodes suffer from uncontrolled dendrite growth and consequent interfacial instability, which result in an unacceptable level of performance in cycling stability and safety. Herein, it is reported that a marginal amount (1.5 at%) of magnesium (Mg) doping alters the surface properties of Li metal foil drastically

Organosulfur polymers have emerged as promising electrode materials for lithium–sulfur (Li–S) batteries, mainly because of their ability to incorporate and stabilize high sulfur content. The low ionic and electronic conductivity of these polymers, however, limit their cycling performance at high active mass loadings. Moreover, Li–polysulfide (Li–PS) shuttling, a fatal phenomenon in the cyclability of Li–S batteries, can be mitigated via the entrapment of Li–PS by utilizing various supramolecular

By comparison between amorphous and crystalline phases, we elucidate that the local structural factor of Fe–O has an impactful contribution to the electronic states of Fe boosting of OER catalytic activity in perovskite-type nickel oxides.

The nonlinear current-voltage relationship and the subsequent threshold voltage in polycrystalline CaCu3Ti4O12 are found to be easily controlled by simply doping a small amount of supervalent cations, Nb5+ and Ta5+. The authors show that the dopants have a significant effect on the reduction of the electrostatic potential at the grain boundaries, scarcely changing the conductance of the bulk grains. Through microcontact analysis and impedance spectroscopy, the control of the potential barrier at

It is shown that CaCu3Ti4O12 grains in a polycrystalline specimen have domains and comparatively thick domain walls. The orientations of the domains within a grain were observed to be slightly tilted toward each other, suggesting the presence of lattice distortions. Multiple reflection spots in the electron diffraction pattern and misfit dislocations were also found in the domain walls. Kelvin probe force microscopy showed the variation in the surface potential of a grain by external electric fi

Abstract A grain boundary forms as an internal interface when two crystalline grains with mutually different crystallographic orientations are in direct contact with each other. As a result, atomic arrangement at grain boundaries differs from that of the bulk, showing serious displacements deviating from the original symmetric positions. As these symmetry‐broken configurations are difficult to achieve in the bulk crystals, grain boundaries are considered distinctive platforms that can exhibit ne

By using a combination of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, ab initio density-functional theory calculations, and neutron powder diffraction techniques, We have found completely different configurations of the antisite exchange defects in LiMnPO4 and LiFePO4, with a random distribution of the exchange pairs without aggregation in the former and with zigzag-type clustering behavior preferred in the latter. Recalling the compositional ana