Tsuyoshi Takami

The crystal structures of the perovskites ${R}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Co}{\mathrm{O}}_{3}$ ($R=\mathrm{La}$, Pr, and Nd) with $0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.3$ were refined from x-ray powder diffraction spectra with the Rietveld method. The result of the Rietveld analyses indicates the presence of three unequal Co-O bonds with different lengths for all samples, and we found that the difference between the two Co-O(2) bond lengths increases with temperature a

We studied the thermoelectric properties of polycrystalline samples of the n=1–5 members of the homologous series An+2Con+1O3n+3, where A represents Ca, Sr, or an appropriate combination of Sr and Ba. The electrical resistivity (ρ) decreased monotonically with increasing temperature in all samples. With increasing temperature, the Seebeck coefficient (S) of the n=1 sample decreased, while S of the n=2–5 samples increased up to about 900 K. The power factor (=S2/ρ) increased with temperature in a

All-solid-state fluoride-ion batteries (FIBs) are expected to become the next generation of battery systems owing to their outstanding energy storage characteristics. However, the volume expansion of the cathode that accompanies the insertion of fluoride ions remains an urgent issue to be addressed. Even if an intercalation-type cathode is applied in FIBs, fluoride-ion insertion into the interstitial sites of two-dimensional materials such as LaSrMnO4 still leads to non-negligible volume expansi

Electronics, which harnesses the properties of electrons, has made remarkable progress since its inception and is a cornerstone of modern society. Ionics, which exploits the properties of ions, has also had a profound impact, as demonstrated by the award of the Nobel Prize in Chemistry in 2019 for achievements related to lithium-ion batteries (LIBs). Ionic conduction in solids is the flow of carrier ions through a solid owing to an electrical or chemical bias. Some ionic materials have been stud

We synthesize a Bi0.7Fe1.3O1.5F1.7 (BFOF) phase via a non-topochemical reaction with a fluorination agent. The crystal structure is refined by Rietveld refinement on the neutron diffraction patterns as a hexagonal lattice in the R3¯ space group, along with the defect structure. The sudden decrease in magnetic susceptibility below 250 K and the linear relationship between the magnetization and the magnetic field indicate that BFOF is an antiferromagnetic material. When BFOF is used as a cathode i

We report on the preparation of conventional and nanosized crystals of the quasi-one-dimensional compounds, ${\text{Ca}}_{3}{\text{Co}}_{2}{\text{O}}_{6}$ and ${\text{Sr}}_{6}{\text{Co}}_{5}{\text{O}}_{15}$, which are potential candidates for thermoelectric materials at higher temperatures; phonon scattering in nanosized crystals reduces the thermal conductivity. Simultaneous modification of the particle size and the oxygen content by milling processes is found to be critical not only for reduci

For the past decade or so, oxide electrolytes have been more intensively investigated as solid electrolytes instead of liquid ones because of their safer handling, more sophisticated device architectures, and potentially higher energy/power densities. Among them, however, studies on transition metal ion-bearing oxide electrolytes have been so far limited to the family of compounds characterized by d0 valence states such as La2/3–xLi3xTiO3, Li7La3Zr2O12, and LixLa(1–x)/3NbO3. Unfortunately, other

This book explores why cobalt oxides have drawn interest as functional materials due to their peculiar physical properties partially originating from a rich variety of the valence and spin state of cobalt ions. The book starts with the basics of condensed matter physics and advances toward the strong electron correlation system stage. It also provi

The valence and spin–state distributions of Co ions and the complex structure of antiferromagnetic Ba 2 Co 9 O 14 have led to the suggestion that doped Ba 2 Co 9 O 14 compounds may be good thermoelectric materials. We have checked this suggestion by measuring the magnetic properties as well as the transport properties of nominal Ba 1.9 A 0.1 Co 9 O 14 ( A =La or Na). We show that although all compounds are indicated to be single phase by powder X-ray diffraction analysis, they are all p -type po

Fluoride cathode materials that undergo conversion reactions such as FeF3 have attracted increasing interest owing to their high energy density. However, the ability of FeF3 to maintain a high capacity over repeated cycles and the decisive factor dominating conversion reactions have yet to be elucidated. By optimizing the choice of lithium salts and electrolyte solutions, we are able to achieve good capacity retention for an FeF3-based cathode, that is, 4.5-fold enhancement compared with a model

We studied the magnetic and thermoelectric properties of the homologous series An+2CoBnO3n+3 (A=Ca,Sr, B=Co,Rh,Ir; n=1–3), which possess one-dimensional chain structures consisting of one CoO6 trigonal prism and n BO6 octahedra. Both Ca3CoRhO6 and Ca3CoIrO6, the n=1 members, exhibited an abrupt drop in the magnetic susceptibility (χ) at around 35K with decreasing temperature. A broad peak was observed in the χ-T curves at 13 and 5K, respectively, for the n=2 and 3 samples of the B=Rh series. The

$^{59}\text{C}\text{o}$ nuclear magnetic resonance (NMR) measurements have been performed to study the local magnetic properties of the misfit layered cobalt dioxides (MLCO's) with the ${\text{CoO}}_{2}$ and rock-salt layers, ${[{\text{Ca}}_{2}{\text{CoO}}_{3}]}_{0.62}{\text{CoO}}_{2}$ $(\ensuremath{\equiv}{\text{Ca}}_{3}{\text{Co}}_{3.92}{\text{O}}_{9.34})$ and ${\text{Ca}}_{3}{\text{Co}}_{3.92}{\text{O}}_{9.34\ensuremath{-}\ensuremath{\delta}}$ with oxygen nonstoichiometry. The $^{59}\text{C}\