Development of "Rattling" Oxide Thermoelectric Materials with Cage-like Crystal Structure

2015 Fiscal Year Final Research Report

• Project/Area Number: 25620152
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Energy-related chemistry
• Research Institution: Kyushu University
• Principal Investigator: Ohtaki Michitaka 九州大学, 総合理工学研究科(研究院), 教授 (50223847)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: β－パイロクロア型酸化物 / かご状結晶構造 / ラトリング / フォノン散乱 / 熱伝導率 / 熱電変換材料 / 非調和振動 / ラマンスペクトル

Outline of Final Research Achievements

Although there has been no report on “rattling” oxides with the “rattler-in-a-cage” structure, here we report the thermal properties of defect pyrochlore (β-pyrochlore) oxides with smaller cations in an oversized cage-like crystal structure. It was clearly shown for the first time that the thermal diffusivity, α, and the thermal conductivity, κ, are lower for the oxides containing lighter A-site cations, contradicting to the conventional prediction of the phonon thermal conductivity, in which lighter comprising atoms must give higher κ. The findings including the Raman spectra of the samples directly evidenced the “rattling” effect of the loosely bound cations on the thermal transport properties of the oxides. The κ values of these oxides are extremely low (below 1.0 W/mK). Although their electrical conductivity was still insufficient, an appropriate selection of the framework composition enabled us to have better thermoelectric performance.

Free Research Field

無機材料化学、工業物理化学