Elastic and dynamical structural properties of La and Mn-doped SrTiO studied by neutron scattering and their relation with thermal conductivities

LaおよびMnを置換したSrTiOの静的・動的構造およびそれらの熱伝導度との関係に関する中性子散乱による研究

梶本 亮一  ; 中村 充孝   ; 村井 直樹  ; 社本 真一  ; 本田 孝志*; 池田 一貴*; 大友 季哉*; 畑 博人*; 江藤 貴弘*; 野田 正亮*; 桑原 英樹*; 奥田 哲治*

Kajimoto, Ryoichi; Nakamura, Mitsutaka; Murai, Naoki; Shamoto, Shinichi; Honda, Takashi*; Ikeda, Kazutaka*; Otomo, Toshiya*; Hata, Hiroto*; Eto, Takahiro*; Noda, Masaaki*; Kuwahara, Hideki*; Okuda, Tetsuji*

The electron-doped SrTiO exhibits good thermoelectric properties, which makes this material a promising candidate of an n-type oxide thermoelectric device. Recent studies indicated that only a few percent co-doping of La and Mn in SrTiO substantially reduces the thermal conductivity, thereby greatly improving the thermoelectric figure of merit at room temperature. Our time-of-flight neutron scattering studies revealed that by doping both La and Mn into SrTiO, the inelastic scattering spectrum shows a momentum-independent increase in the low-energy spectral weight approximately below 10 meV. The increase in the low-energy spectral weight exhibits a clear correlation with thermal conductivity. The correlation is attributed to dynamical and local structural fluctuations caused by the Jahn-Teller instability in Mn ions coupled with the incipient ferroelectric nature of SrTiO, as the origin of the low thermal conductivity.