High Thermopower with Metallic Conductivity in p-Type Li-Substituted PbPdO2

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• 作者：Leo K. Lamontagne ; Geneva Laurita ; Michael W. Gaultois ; Michael Knight ; Leila Ghadbeigi ; Taylor D. Sparks ; Markus E. Gruner ; Rossitza Pentcheva ; Craig M. Brown ; Ram Seshadri
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：May 24, 2016
• 年：2016
• 卷：28
• 期：10
• 页码：3367-3373
• 全文大小：429K
• 年卷期：0
• ISSN：1520-5002

文摘

PbPdO₂ is a band semiconductor with a band gap arising from the filled d⁸ nature of square-planar Pd²⁺. We establish that hole doping through Li substitution for Pd in PbPdO₂ results in a p-type metallic oxide with a positive temperature coefficient of resistance for substitution amounts as small as 2 mol % Li for Pd. Furthermore, PbPd_1–xLi_xO₂ demonstrates a high Seebeck coefficient and is therefore an oxide thermoelectric material with high thermopower despite the metallic conductivity. Up to 4 mol % Li is found to substitute for Pd as verified by Rietveld refinement of neutron diffraction data. At this maximal Li substitution, the resistivity is driven below the Mott metallic maximum to 3.5 × 10^–3 Ω cm with a Seebeck coefficient of 115 μV/K at room temperature, which increases to 175 μV/K at 600 K. These electrical properties are almost identical to those of the well-known p-type oxide thermoelectric Na_xCoO₂. Nonmagnetic Li-substituted PbPdO₂ does not possess a correlated, magnetic state with high-spin degeneracy as found in some complex cobalt oxides. This suggests that there are other avenues to achieving high Seebeck coefficients with metallic conductivities in oxide thermoelectrics. The electrical properties coupled with the moderately low lattice thermal conductivities allow for a zT of 0.12 at 600 K, the maximal temperature measured here. The trend suggests yet higher values at elevated temperatures. First-principles calculations of the electronic structure and electrical transport provide insight into the observed properties.