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We investigated single crystals of ${\mathrm{Ba}}_{3\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Nb}}_{5}{\mathrm{O}}_{15}$ with a tetragonal tungsten bronze (TTB) structure, which exhibits a metal-insulator transition with $x$. We found that there is a one-dimensional anisotropy with a higher dc conductivity along the $c$ axis in the metallic phase, but it disappears in the insulating phase. The optical conductivity spectra of the metallic samples show similar anisotropy to the dc conductivity, but the anisotropy persists even in the insulating phase. These experimental results, together with the result of magnetic susceptibility, indicate that the disorder caused by the Sr ions loosely bound to the surrounding oxygen ions plays an important role in the metal-insulator transition.

The authors show that the nonvolatile positive magnetoresistance observed in a ferrimagnet La${}_{5}$Mo${}_{4}$O${}_{16}$ is caused by the electrical conduction along the magnetic domain walls.

We investigated the structural, magnetic, transport, and high-temperature thermoelectric properties of single crystals of the pseudobrookite ${\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{2+x}{\mathrm{O}}_{5}$ for $0\ensuremath{\le}x\ensuremath{\le}1$ grown using a floating zone. We found a correlation of spin-singlet ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{3+}$ dimers coupled with the lattice even in the conductive $\ensuremath{\alpha}$ and $\ensuremath{\lambda}$ phases which develops with increasing $x$. This developing dimer correlation reduces the number of unpaired ${\mathrm{Ti}}^{3+}$ ions, which makes the compound more conductive owing to the suppression of disorder for $x$ up to about 0.75. The dimer fluctuation causes a critical enhancement of the magnetic susceptibility at around 150 K in the $\ensuremath{\lambda}$ phase near the boundary ($x\ensuremath{\sim}0.9$) between the $\ensuremath{\lambda}$ and the $\ensuremath{\beta}$ phases. Such a correlation of the spin-singlet ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{3+}$ dimers may produce a high Seebeck coefficient in the conductive $\ensuremath{\alpha}$ and $\ensuremath{\lambda}$ phases leading to a large thermoelectric power factor at high temperatures.

We performed a pump–probe optical reflectivity measurement with an applied uniaxial strain for bulk single crystals of BaV10O15 at room temperature. We found that with a compressive strain of ΔL/L ...

We studied single crystals of orthorhombic ${\mathrm{Sr}}_{2}{\mathrm{VO}}_{4}$ containing spin-singlet dimers of ${\mathrm{V}}^{4+}\phantom{\rule{0.28em}{0ex}}(3{d}^{1})$ and those with Ti or Nb substituted for V. We found that both Ti and Nb dopings induce the evolution of a Curie-Weiss component in the magnetic susceptibility, but the rate of evolution with doping is several times higher for Nb doping. We also found that Nb doping induces the conduction of $d$ electrons. These results can be explained by the hybridization of the Nb $4d$ states with the $3d$ states of the neighboring V ions, possibly causing rearrangement of the $d$ electron in the doubly degenerate $e$ states in the V ion.

By using a technique of thermoreflectance that can precisely measure the thermal conductivity of thin films, we found that the thermal conductivity of ${\mathrm{SrVO}}_{3}\text{\ensuremath{-}}{\mathrm{SrTiO}}_{3}$ multilayer thin films normal to the surface was substantially reduced by decreasing the thickness of each layer. This indicates that a large intrinsic thermal resistance exists at the interface between ${\mathrm{SrVO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$ in spite of the similar phononic properties for these two compounds.

${\mathrm{Ba}}_{0.9}{\mathrm{Sr}}_{0.1}{\mathrm{V}}_{13}{\mathrm{O}}_{18}$ exhibits two ordered phases caused by the charge/orbital ordering of the $d$ electrons on the V ions. We have succeeded in observing photoinduced phase transitions over three phases in this compound: a transition from the low-temperature phase to the high-temperature phase within 0.3 ps, followed by a transition to the intermediate-temperature phase within 2 ps. The relationship between the symmetry at each of the three phases plays a key role in the dynamics of the photoinduced phase transitions in such a compound.