arXiv subjects

Hiroki Taniguchi

Publications and source records attributed to Hiroki Taniguchi.

23 records · Page 2Linked to original sources

arXiv2013

X-ray crystal structure analysis and the Ru valence of Ba4Ru3O10 single crystals

We present the single-crystalline x-ray diffraction study on the Ba4Ru3O10 consisting of the corner-shared Ru3O12 trimers. The crystal structure is re-determined from 78 to 300 K across an antiferromagnetic transition at 105 K. The orthorhombic symmetry (Cmca, space group No. 64) is preserved at all temperatures measured. This structure presents exceptionally long Ru-O distances characterized by a significant distribution within the Ru3O12 trimer. A bond valence sum calculation suggests that the charge disproportionation within the Ru3O12 trimer emerges even at room temperature, which we ascribe to molecular orbital formation in the Ru3O12 trimer, as supported by recent theoretical calculations. Based on the analyzed crystal structure, the electronic states and the nature of the phase transition at 105 K are discussed.

cond-mat.str-el↗

arXiv2013

Pb(Mg1/3Nb2/3)O3 (PMN) Relaxor: Dipole Glass or Nano-Domain Ferroelectric ?

Combining our comprehensive investigations of polarization evolution, soft-mode by Raman scattering and microstructure by TEM, and the results reported in the literatures, we show that prototypical relaxor Pb(Mg1/3Nb2/3)O3 (PMN) is essentially ferroelectric for T<Tc~225 K. Its anomalous dielectric behavior over a broad temperature range results from the reorientation of domains in the crystal. A physic picture of the structure evolution in relaxor is also revealed. It is found that nanometric ferroelectric domains (gennerally called as polar nano-region (PNR)) interact cooperatively to form micrometric domain. Such multiscale inhomogeneities of domain structure in addition to the well-known inhomogeneities of chemical composition and local symmetry are considered to play a crucial role in producing the enigmatic phenomena in relaxor system.

cond-mat.mtrl-sci↗

arXiv2012

Ferroelectricity Driven by Twisting of Silicate Tetrahedral Chains

Conventional perovskite-type ferroelectrics are based on octahedral units of oxygen, and often comprise toxic Pb to achieve robust ferroelectricity. Here, we report the ferroelectricity in a silicate-based compound, Bi2SiO5 (BSO), induced by a structural instability of the corresponding silicate tetrahedral chains. A low-energy phonon mode condenses at ~ 673 K to induce the proper ferroelectric phase transition. Polarization switching was observed in a BSO single crystal with a coercive field of 30 kV/cm and a spontaneous polarization of 0.3 microC/cm2 along a direction normal to the cleavage plane. The in-plane polarization was estimated by first principles calculations to be 23 microC/cm2. The present findings provide a new guideline for designing ferroelectric materials based on SiO4 tetrahedral units, which is ubiquitously found in natural minerals.

cond-mat.mtrl-sci↗

arXiv2011

Ferroelectricity of Li-doped silver niobate (Ag,Li)NbO3

Phase evolution in (Ag1-xLix)NbO3 (ALN) solid solution was investigated by X-ray diffraction technique, dielectric and polarization measurements. It is shown that small substitution of Ag with Li gives rise to an orthorhombic-rhombohedral structural transformation in ABO3-perovskite silver niobate at room temperature. Structural refinements indicate that both A- and B-site displacements contribute to the spontaneous polarization of the ferroelectric phase with symmetry R3c. Increasing Li-concentration enhances the ferroelectric rhombohedral distortion, resulting in the increase of the para-ferroelectric phase transition temperature and the polarization of the solid solutions.

cond-mat.mtrl-sci↗

arXiv2009

Ferroelectric Soft Mode in Pb(Mg1/3Nb2/3)O3

Ferroelectric soft mode in Pb(Mg1/3Nb2/3)O3 (PMN) has been clearly resolved by precision Raman scattering measurements for the first time. A polarization direction of the incident laser was chosen along [110] in cubic configuration in order to eliminate strong scattering components around 45 cm-1, which always smeared the low-frequency spectra of PMN. The soft mode frequency omega_s (=\sqrt{omega_0^2-gamma^2}) softens around 200 K, where omega_0 and gamma are a harmonic frequency and a damping constant, respectively. The present result evidenced that the origin of the polarizationthe in PMN is the soft mode.

cond-mat.mtrl-sci↗