掲載種別：研究論文（学術雑誌）  

The ZnSb binary system contains two high-performing thermoelectric materials, namely the ordered ZnSb and the disordered Zn13Sb10. Both systems exhibit low thermal conductivity, which is speculated to originate from multicentre bonding within Zn2Sb2-rhombi. Here, the electron density of ZnSb is reported based on multipole modelling of accurate X-ray diffraction data measured at 20 K. Topological analysis reveals that the bond paths in the rhombus are endocyclically strained and that electron density is concentrated within the rhombus rather than along its geometric bonds consistent with a multicentre bond description. However, the electron density is not equally shared between the geometric bonds of the rhombus. Electron density analysis and modelling of low-temperature anharmonicity reveal that one Zn-Sb interaction is weaker than the other. Taken together with the orientation of bonds external to the rhombus structure, an alternative description emerges wherein the multicentre bond is more partially localised along one set of the opposite legs of the rhombus. In this description, the stronger bond can be considered a traditional 2-centre-2-electron bond, while the weaker interaction is coordinative to the covalent bond. The anharmonicity and low thermal conductivity may consequently be understood as Zn rattling along the coordinative interaction. ZnSb is an excellent thermoelectric material exhibiting low thermal conductivity. Here, the chemical bonding origin of anharmonicity in ZnSb is revealed through quantitative analysis of the crystal electron density obtained through multipole modelling of highly accurate synchrotron X-ray diffraction data measured at 25 K. image

DOI： 10.1002/adfm.202401703

掲載種別：研究論文（学術雑誌）  

DOI： 10.1107/S2052520624004104

掲載種別：研究論文（学術雑誌）  

A rattling of silver (Ag) atoms is identified in the low-temperature phase of Argyrodite compound Ag8SnSe6 through a systematic multitemperature synchrotron radiation powder diffraction study. Both Bragg and diffuse scatterings from the sample can be well explained by the presence of the Ag rattling atoms. The Rietveld refinements of the low-temperature phase were significantly improved by introducing anisotropic thermal motions of Ag1 and Ag3 sites. The diffuse scattering observed in the low-temperature phase can be well explained by a combination of the first-order thermal diffuse and liquid-like scatterings, which arise due to the rattling of Ag1 and Ag3 sites. The rattling of Ag1 and Ag3 sites is restricted in the perpendicular direction of the Se triangles. This behavior is very similar to that of rattling atoms in the tetrahedrite and tennantite. The present findings are consistent with the low thermal conductivity observed in the low-temperature phase and the existence of low-energy excitation due to neutron scattering.

DOI： 10.1021/acs.cgd.4c00511

掲載種別：研究論文（学術雑誌）  

Ultrasmall metal oxide nanoparticles (<5 nm) potentially have new properties, different from conventional nanoparticles. The precise size control of ultrasmall nanoparticles remains difficult for metal oxide. In this study, the size of CeO2 nanoparticles was precisely controlled (1.3-9.4 nm) using a continuous-flow hydrothermal reactor, and the atomic distortion that occurs in ultrasmall metal oxides was explored for CeO2. The crystalline nanoparticles grow rapidly like droplets via coalescence, although they reach a critical particle size (similar to 3 to 4 nm), beyond which they grow slowly and change shape through ripening. In the initial growth stage, the ultrasmall nanoparticles exhibit disordered atomic configurations, including stacking faults. In ultrasmall CeO2 nanoparticles (<3 to 4 nm), unusual electron localization occurs on Ce 4f orbitals (Ce3+) as a result of O disordering, regardless of O vacancy concentration. This behavior differs from ordinary electron localization caused by the presence of O vacancies. The ultrasmall metal oxides have extraordinary distortion states, making them promising for use in nanotechnology applications. Furthermore, the proposed synthesis method can be applied to various other metal oxides and allows exploration of their properties.

DOI： 10.1021/jacs.4c05106