弾性・非弾性散乱データ同時解析による計測物質科学の創成

科学研究費助成事業 研究成果報告書：挑戦的萌芽研究2016-2017課題番号 : 16K1366

Tightly binding valence electron in aluminum observed through X-ray charge density study

Accurate and high reciprocal resolution experimental structure factors of aluminum were determined from a synchrotron powder X-ray diffraction data measured at 30 K with sin θ/λ < 2.31 Å−1. The structure factors have small deviations from independent atom model in sin θ/λ < 0.83 Å−1. Theoretical structure factors were prepared using density functional theoretical calculations by full potential linearized augmented plane wave method. The deviation between experimental and theoretical data was also observed at around sin θ/λ ≈ 0.4 Å−1. The charge density was determined by an extended Hansen-Coppens multipole modeling using experimental and theoretical structure factors. Charge density maxima at tetrahedral site were observed in both experimental and theoretical deformation density. The charge-density difference peaks indicating directional bonding formation were observed in the difference density between experiment and theory. The present study reveals tight binding like character of valence electron of aluminum. The fact will provide a crucial information for development of high-performance aluminum alloy

Structure factors and charge-density study of diamond at 800 K

The structure factors of diamond were determined by synchrotron radiation X-ray powder diffraction at 800 K at sin θ/λ ≤ 2.2 Å−1 reciprocal resolution. The structure factors were estimated using six powder profiles measured on beamline BL02B2 at SPring-8 (Hyogo, Japan). A high reciprocal resolution at sin θ/λ ≤ 2.2 Å−1 was required to reveal the temperature dependence of the charge density, due to the high Debye temperature of θD = 1860 K of diamond. Wide 2θ angle data with the highest counting statistics are crucial for accurate data analysis. The periodic noise of every six-pixel step was observed in the highest counting statistics imaging plate (IP) data scanned by a BAS2500 IP scanner. It was found that the noise originated from the six-sided polygonal mirror in the scanner. The intensity fluctuation at every six-pixel step was also found in the Fourier series expansion of the powder profiles. The ratio of the maximum fluctuation was estimated as 0.4% by summing all six-pixel step data. The powder profiles were corrected by multiplying the ratios. The intensity fluctuation in the background region was reduced to less than 50% of the uncorrected data. The weak 888 Bragg reflection, with an intensity of 0.005% of that of the 111 Bragg reflection at 800 K, was readily observed in the corrected data. Finally, the structure factors determined at 800 K were successfully applied to a charge-density study by multipole modelling. The reliability factors and multipole parameters at 800 K are in agreement with those at 300 K. The differences in the charge density at the bond midpoint and ∇2ρ at the bond-critical point were less than 1% and 2%, respectively

Aspherical and covalent bonding character of d electrons of molybdenum from synchrotron x-ray diffraction

The occupancies and spatial distribution of electrons for 4d-orbitals in pure molybdenum have been experimentally determined by a charge density study from synchrotron radiation x-ray powder diffraction. There are valence charge density maxima in interatomic positions indicating bond formation. The electron deficiencies of Γ12 orbitals were visualized in the observed static deformation density. An electron deficiency of ~0.5 was observed from the orbital population analysis through multipole refinement. The occupancies and spatial distribution have also been calculated by a density functional theoretical calculation using WIEN2k packages for comparison. The observed features agree well with the theoretical study. In addition, the observed charge density has more covalent bonding character than the theoretical one. The present study confirms that a state-of-the-art x-ray charge density study can reveal the spatial structure of d-electrons in 4d-system

Structure analysis of Zn-Mg-Ho icosahedral quasicrystal by modified Rietveld method using ellipsoid and sphere windows

A structure analysis of Zn-Mg-Ho icosahedral quasicrystal was carried out by the powder X-ray diffraction method using synchrotron radiation (Lambda=0.73490 A) at SPring-8. The intensity distribution was analyzed by the Rietveld method modified for an icosahedral quasicrystal, in which simplified models were assumed: ellipsoid and spherical windows were assumed at five crystallographic sites in a F-type hypercubic unit cell. The analysis revealed the presence of an almost perfect Penrose tiling with edge length 5.20 A. The vertices are occupied alternatively by Zn and Mg, and almost all of the edge centers of the Penrose rhombohedra are occupied by 0.8Zn and 0.2Mg. Ho and Mg atoms tend to be present on the body diagonal of the prolate rhombohedra. Good agreement between the measured and calculated intensity distribution using the simplified model suggests the applicability and the limitation of structure analysis using the powder X-ray diffraction method.Comment: 10 pages, 3 tables, 3 figure

Disordered zinc in Zn_4Sb_3 with phonon-glass and electron-crystal thermoelectric properties

By converting waste heat into electricity, thermoelectric generators could be an important part of the solution to today's energy challenges. The compound Zn_4Sb_3 is one of the most efficient thermoelectric materials known. Its high efficiency results from an extraordinarily low thermal conductivity in conjunction with the electronic structure of a heavily doped semiconductor. Previous structural studies have been unable to explain this unusual combination of properties. Here, we show through a comprehensive structural analysis using single-crystal X-ray and powder-synchrotron-radiation diffraction methods, that both the electronic and thermal properties of Zn_4Sb_3 can be understood in terms of unique structural features that have been previously overlooked. The identification of Sb^(3-) ions and Sb_2^(4-) dimers reveals that Zn_4Sb_3 is a valence semiconductor with the ideal stoichiometry Zn_(13)Sb_(10). In addition, the structure contains significant disorder, with zinc atoms distributed over multiple positions. The discovery of glass-like interstitial sites uncovers a highly effective mechanism for reducing thermal conductivity. Thus Zn_4Sb_3 is in many ways an ideal 'phonon glass, electron crystal' thermoelectric material

Effects of Substituents on the Blue Luminescence of Disilane-Linked Donor‒Acceptor‒Donor Triads

A series of disilane-linked donor‒acceptor‒donor triads (D‒Si‒Si‒A‒Si‒Si‒D) was synthesized to investigate the effects of substituents on the photophysical properties. The triads were prepared by metal-catalyzed diiodosilylation of aryl iodides using a Pd(P(t-Bu)3)2/(i-Pr)2EtN/toluene system that we previously developed. Optical measurements, X-ray diffraction analysis, and density functional theory calculations revealed relationships between the photophysical properties and molecular structures of these triads in solution and in the solid state. The compounds emitted blue to green fluorescence in CH2Cl2 solution and in the solid state. Notably, compound 2 showed fluorescence with an absolute quantum yield of 0.17 in the solid state but showed no fluorescence in CH2Cl2. Our findings confirmed that the substituent adjacent to the disilane moiety affects the conformations and emission efficiencies of compounds in solution and in the solid state

Structural Modulations in the Intermediate Phase of Antiferroelectric PbHfO3

金沢大学国際基幹教育院We determine the crystal structure of the intermediate antiferroelectric (A2) phase of PbHfO3 by a Rietveld method using X-ray and neutron diffraction. The structure can be described by modulations associated with the lattice vibrational mode Σ3(TO) with q (0.15,0.15,0)and the Rxy 25 mode, although the latter modulation is relatively distorted. The size of the orthorhombic unit cell is p2 × 10p2 × 2 times as large as that of the high-temperature cubic cell. The space group is Pbam-D9 2h (No. 55), and is the same as that of the room-temperature antiferroelectric (A1) phase of PbHfO3. © 2018 Physical Society of Japan. All rights reserved.Embargo Period 12 month