2017 APS March Meeting, New Orleans, LA - Oral (Y36.00002)
Session Y36: Thermoelectrics: Characterization, Nanostructures, 11:51 AM–12:03 PM, Friday, March 17, 2017
Title: NMR study of partially filled skutterudites AxCo4Sb12 (A = Yb, Ba, Sr, Ca) and BaxYbyCo4Sb12.
Abstract Body: Partially filled Co-Sb skutterudites have been of considerable interest as thermoelectric materials, particularly with multiple filling for which high ZT values can be obtained. This is due in part to control of phonon thermal conductivity, but also the change in composition leads to subtle changes in electronic behavior as well as magnetism due both to rare earth filler atoms and to native defects. We measured Co NMR on several partially filled AxCo4Sb12 skutterudites in order to investigate such behavior. From the T-dependent NMR shifts along with T1 relaxation times we can separate metallic shift contributions from those due to local moments. We compare the results to predicted band-edge behavior with multiple minima, and the estimated g factors, by matching this behavior to transport measurements. Also the behavior of Yb-filled samples provides an estimate of the conduction band mediation of the magnetic response, and we also find magnetic shifts in Ba-doped skutterudite which we address in terms of Co mixed-valence behavior.
Funding Acknowledgement: This work was supported by the Robert A. Welch Foundation, Grant No. A-1526. Synthesis work was partly supported by the Center for Solar and Thermal Energy Conversion and a Grant-in-Aid for Scientific Research (B) (No. 23340092) from the Japan Society.