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

Abstract

PbPdO 2 is a band semiconductor with a band gap arising from the filled d 8 nature of square-planar Pd 2+ . We establish that hole doping through Li substitution for Pd in PbPdO 2 results in a p-type metallic oxide with a positive temperature coefficient of resistance for substitution amounts as small as 2 mol % of Li for Pd. Furthermore, PbPd 1−x Li x O 2 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 maximum 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 the well-known p-type oxide thermoelectric Na x CoO 2 . Nonmagnetic Li-substituted PbPdO 2 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 = 0.12 at 600 K; the maximum 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.

Electron–phonon coupling in APd3O4: A = Ca, Sr, and Sr0.85Li0.15

“…Hence, it is very important to understand phonons and their correlation with electronic degrees of freedom in these systems. APd3O4 (A = Ca and Sr) systems may also be suitable for thermoelectric applications such as switching and sensing devices due to their narrow bandgap [17,21,23].…”

Inducing n - and p -Type Thermoelectricity in Oxide Superlattices by Strain Tuning of Orbital-Selective Transport Resonances

“…Transition metal oxides are attractive for thermoelectric applications owing to their chemical and thermal stability and environmental friendliness as well as to the prominent role of electronic correlations. 1,2 Considerable experimental and computational 3 research aims at finding oxide thermoelectrics with improved performance, mostly among bulk materials by doping [4][5][6][7] or strain. 8 An alternative strategy is to exploit heterostructuring and dimensional confinement.…”

The Role of Structural and Compositional Heterogeneities in the Insulator-to-Metal Transition in Hole-Doped APd3O4 (A = Ca, Sr)

“…22,23 Recently, we have observed a high Seebeck coefficient with metallic conductivity in the complex palladium oxide PbPdO 2 when it undergoes an insulator-to-metal transition with Li-substitution. 24 A better understanding of the insulator-to-metal transitions can lead to improvements in the functional properties of these and other oxide materials.…”