Masatomo Yashima 교수

A structural phase transition between the cubic (space group, Fm 3 m) and tetragonal (space group, P 4 2 /nmc) phases in a zirconia–ceria solid solution (Zr 1−x Ce x O 2 ) has been observed by Raman spectroscopy. The cubic–tetragonal ( c–t″ ) phase boundary in compositionally homogeneous samples exists at a composition X 0 (0.8 < X 0 < 0.9) at room temperature, where t ″ is defined as a tetragonal phase whose axial ratio c/a equals unity. The axial ratio c/a decreases with an increase of c

We report the results of a neutron powder diffraction study of the La(0.62)Li(0.16)TiO3 perovskite that determined the diffusion path of lithium cations at room temperature. At 77 K, the Li cations are located at the 2c site (Wycoff notation of the Cmmm space group) on the (002) La deficient layer, while, at room temperature, they are spread over a wide area and migrate following the 2c-4f-2c or 2c-2d-2c tie line on the (002) layer. The probability density of Li cations has a minimum between the

In the ZrO 2 -YO 1.5 solid solutions, the phase changes among the cubic phase (Fm3m, Z=4), the t″ form and the t' form were investigated by neutron and X-ray powder diffraction, where the t″ and t' forms are defined as tetragonal phases (P4 2 /nmc, Z=2) with axial ratios of c/a f =1 and c/a f >1, respectively, which were prepared by a diffusionless transition from the high-temperature cubic phase during quenching. a f is the lattice parameter of the pseudo-fluorite cell

A size effect on crystal structure has been investigated for barium titanate (BaTiO3) nanoparticles of 40-, 140-, and 430-nm sizes, by means of neutron and high-resolution synchrotron x-ray powder-diffraction and Raman-scattering techniques. These samples were prepared by a modified two-step thermal decomposition method from barium titanyl oxalate, resulting in very few lattice impurities. Rietveld analysis of the neutron-diffraction data for the 430-nm- and 140-nm-sized BaTiO3 particles was per

Crystal structure of ferroelectric silver niobate AgNbO3 was determined (Pmc21) by convergent beam electron, electron, neutron, and synchrotron diffraction techniques and first-principles calculations. The atomic displacements along the c axis in Pmc21 AgNbO3 are responsible for the spontaneous polarization, ferroelectricity, and the paraelectric−ferroelectric phase transition.

MEM nuclear density analysis from neutron diffraction data measured in situ at 1015.6 degrees C has indicated the two-dimensional network of curved O2-O3-O2 oxide-ion diffusion paths on the (Pr,La)-O layer in a K2NiF4-type structured oxide-ionic and electronic mixed conductor (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+delta.

Oxide-ion conductors are important in various applications such as solid-oxide fuel cells. Although zirconia-based materials are widely utilized, there remains a strong motivation to discover electrolyte materials with higher conductivity that lowers the working temperature of fuel cells, reducing cost. Oxide-ion conductors with hexagonal perovskite related structures are rare. Herein, we report oxide-ion conductors based on a hexagonal perovskite-related oxide Ba₇Nb₄MoO<su

Zirconia–ceria solid solutions of tetragonal symmetry ( t ’ZrO 2 ) containing 30 to 65 mol% ceria were prepared by annealing c ′‐ZrO 2 at 627°C samples sintered at 1660–1760°C, where c ′‐ZrO 2 is defined as a cubic or tetragonal phase whose axial ratio c/a (tetragonality) is equal to 1. The lattice parameters and the cube root of the unit cell volumes of the annealed samples increased linearly with the ceria content but, on the other hand, the axial ratio c/a (tetragonality) decreased to 1.000 a

High-resolution neutron-diffraction experiments have been performed to study the structural changes of ${\mathrm{ZrO}}_{2}$ induced by ${\mathrm{CeO}}_{2}$ doping. The crystal structures of monoclinic [P${2}_{1}$/c, Z=4] and tetragonal [P${4}_{2}$/nmc, Z=2] phases for ${\mathrm{ZrO}}_{2}$--X mol % ${\mathrm{CeO}}_{2}$ (X=0, 2, 5, 8, 10, 12, and 15) have been refined by the Rietveld analysis of the diffraction patterns measured at 298 K. The unit-cell parameters change anisotropically with an inc