Novel thermoelectric properties of complex transition-metal oxides

Abstract

We report how the thermopower of complex transition-metal oxides is susceptible to small changes in material parameters. In the A-site ordered perovskite oxide R(2/3)Cu(3)Ti(3.6)Ru(0.4)O(12), the thermopower changes from 15 to -100 microV K(-1) at 300 K in going from R = La to Er. We associate this with the hybridization between Cu 3d and Ru 4d electrons, which depends on R. For stronger hybridization, the Cu 3d electrons become more itinerant leading to positive thermopower. In the A-site ordered perovskite cobalt oxide Sr(3)YCo(4)O(10.5), the spin state of the Co(3+) ions determines the magnitude of the thermopower, where partial isovalent substitution (Ca for Sr and Rh for Co) enhances the thermopower whilst keeping the resistivity intact. These substitutions stabilize the low spin state of the Co(3+) ions, which affects the thermopower through the entropy of the background for the carriers. We propose that the control of the magnetism plays a pivotal role in determining the thermopower in a certain class of complex oxides.

Correlation effects in CaCu3Ru4O12

“…The slight changes in intensities in core level XPS 11 are then probably the result of a different effective Ru-Cu hybridization, as it was also suggested from data on thermopower of another set of doping series. 39 We infer from the band structure calculations that it is the particulars of the crystal structure that form the reason for the Cu to possess a divalent state: although the Cu is embedded in a metallic background and could be expected to be well-bound and have a full 3d shell, the planar coordination and the resulting ligand field splitting raise the Cu d x 2 −y 2 orbital in energy. This splitting is strong enough so that the d Whether or not the presence of localized Cu 2+ moments together with the itinerant Ru electrons could lead to the formation of exotic magnetic states, comparable to the Kondo effect in rare earth compounds, depends very much on the energetics and the character of the Cu 3d states closest to the Fermi level.…”

Magnetic and transport properties of the spin-state disordered oxide La0.8Sr0.2CoShibasaki1, Terasaki2, Nishibori3 et al. 2011Phys. Rev. BSelf Cite191120View full textAdd to dashboardCite

“…As discussed above, the spin state and the highest occupied orbital are disordered in this solid solution, which induces additional entropy in the system. Since the thermopower reflects entropy per carrier, 40,70 we expect that the enhanced thermopower found here is related to the entropy due to the disorder in the spin state and/or the highest occupied orbital. In the perovskite-related oxide Sr 3 YCo 4 O 10.5 , 5 partial substitution of Ca for Sr substantially enhances the thermopower, which is associated with the spin-state crossover of the Co 3+ ions.…”

Enhancement of thermoelectric performance in strontium titanate by praseodymium substitution

“…Since most of the energy ($60% 70%) used in the world is discharged as waste heat, "green" thermoelectric conversion received a considerable attention due to simplicity without employing moving parts, silent operation, and excellent scalability and reliability. [1][2][3][4][5] Although oxides have been considered ill suited for thermoelectric power generation, 2 the layered Na 2 CoO 4 oxide was found to show high thermopower along with high electrical conductivity. 2,6 Since this discovery, many efforts were made on exploring new Co-containing oxides demonstrating high thermoelectric performance (Refs.…”

“…At low dopant content, the thermal conductivities of both SrTi(Nb)O 3 and Sr(La)TiO 3 were found to be almost independent on the carrier concentration. 15,16,18,19 Though further addition leads to unfavorable increase in the electronic contribution of thermal conductivity of SrTi(Nb)O 3 , 16 improved phonon scattering provides overall decrease in thermal conductivity in the case of Sr(La)TiO 3 . 17 The latter suggests donor substitution in A-sublattice as a promising strategy to suppress thermal conductivity, whilst increasing the electrical performance of strontium titanate.…”