Elastic and dynamical structural properties of La and Mn-doped SrTiO3 studied by neutron scattering and their relation with thermal conductivities

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

doi:10.1038/s41598-018-27984-z

Abstract

The electron-doped SrTiO3 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 SrTiO3 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 SrTiO3, 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 Mn3+ ions coupled with the incipient ferroelectric nature of SrTiO3, as the origin of the low thermal conductivity.

Highlights

IntroductionThe local Jahn-Teller distortions induced by the co-doping can work as strong phonon scatterers, and the effect is enhanced if they coupled with the inherent structural instability of SrTiO3
Further doping of Mn compared with SLTMO2 does not cause further decrease in κ, and κ for SLTMO4 exceeds that for SLTMO2, it is still substantially lower than κ's for SthTeOs,pSeTciMficOh,eaant,dgSrLoTupOv. eTlhoeciptyh,oannodnmtheearnmfraelecpoantdhuocftipvhitoynκoniss,erxepsrpeescsteidvealsy.κWl =e fo13uCnvdgla, lwl thheerecoCm, vpgo, uannddsl denote exhibit similar values of specific heats at high temperatures doping dependence was reported at low temperatures below 100 K7,17
We examined elastic and dynamical structural properties in La and Mn-doped SrTiO3 by neutron scattering

Summary

Introduction

The local Jahn-Teller distortions induced by the co-doping can work as strong phonon scatterers, and the effect is enhanced if they coupled with the inherent structural instability of SrTiO3. This expectation reminds us the idea for skutterdites and clathrates that local motions of atoms in cages termed as rattling intervene in the heat flows without significantly affecting the electron conductions[11,12,13], later it was revealed that the rattling modes are rather low-lying optical modes with weak interactions with the host lattices[14,15,16]. We performed time-of-flight elastic and inelastic neutron scattering measurements on powder samples of La and Mn-doped SrTiO3, Sr0.95La0.05TiO3 (SLTO), SrTi0.98Mn0.02O3 (STMO), Sr0.95La0.05Ti0.98Mn0.02O3 (SLTMO2), and Sr0.95La0.05Ti0.96Mn0.04O3 (SLTMO4), and non-doped SrTiO3 (STO) to examine the doping dependence of the static as well as dynamical structural properties

Methods

Results

Conclusion