Thermal conductivity reduction in oxygen-deficient strontium titanates

Abstract

We report significant thermal conductivity reduction in oxygen-deficient lanthanum-doped strontium titanate ͑Sr 1−x La x TiO 3−␦ ͒ films as compared to unreduced strontium titanates. Our experimental results suggest that the oxygen vacancies could have played an important role in the reduction. This could be due to the nature of randomly distributed and clustered vacancies, which would be very effective to scatter phonons. Our results could provide a pathway for tailoring the thermal conductivity of complex oxides, which is very beneficial to various applications including thermoelectrics.

Effect of oxygen vacancy distribution on the thermoelectric properties of La-doped SrTiO3 epitaxial thin films

“…The oxygen vacancies partially ionize by localizing the conduction electrons and clustering of such vacancies, which is common in STO films grown by PLD, 46 and can act as localizing sites for the itinerant electrons. 47 The randomly distributed and clustered nature of oxygen vacancies in LSTO has been previously reported 14 to influence the phonon transport. Hence it is reasonable that the co-existence of differently reduced regions in the films dictates the observed degenerate electrical conductivity and non-degenerate Seebeck coefficient.…”

“…It is seen that film A has the highest power factor (0.47 W m À1 K À1 at 510 K). It has been reported that oxygen vacancies effectively scatter phonons in STO, bringing in a marked reduction of lattice thermal conductivity 14 TABLE II. Fitting parameters for the Drude -Lorentz dispersion relation (Eq.…”

“…11 Since the discovery 12 of a high figure of merit (defined as ZT ¼ S 2 rT/j, where S, r , and j are, respectively, the Seebeck coefficient, electrical conductivity, and thermal conductivity) 13 in p-type Na x CoO 2 , the search for an n-type counterpart has intensified, and electron doped STO has been regarded as a potential candidate. However, the high thermal conductivity 14 of STO (3-10 W m À1 K À1 ) limits ZT, with a best reported value of 0.37 in 20% Nb doped STO bulk. 15 The strategies to improve ZT of STO based thermoelectric materials involve enhancement of the electronic transport properties (referred to as the power factor, S 2 rT) and/or engineering the material to impede the phonon propagation to reduce j.…”

Thermal conductivity as a metric for the crystalline quality of SrTiO3 epitaxial layers

“…͑For PLD-3-850, we attribute the shoulder to the right of the substrate peak to originate from some portion of the mosaic within the substrate rather than the film. An extensive analysis of homoepitaxial STO films by Ohnishi et al 4 reported that diffraction by the films only appears to the left of the substrate peak.͒ 19. ͑a͒ Thermal conductivity of MBE grown films.…”

Thermoelectric properties of n-type SrTiO3

“…There have been a number of studies of the thermal conductivity measurements on both the bulk and doped STO at elevated temperatures. [20][21][22][23][24][69][70][71][72] Due to the significant difference of κ between bulk and heavily doped materials, we consider two scenarios with one taking the bulk κ at 300 K (∼11 W m −1 K −1 ) 21,71 and the other using the doped κ at the same T (∼8 W m −1 K −1 , based on moderately doped samples 21,24 ). With the second scenario, we are able to get low κ from 2.3 to 2.5 W m −1 K −1 at 1000 K. These values are in better accord with experiments at high temperatures (∼1000 K).…”