Cross-plane electronic and thermal transport properties of p-type La0.67Sr0.33MnO3/LaMnO3 perovskite oxide metal/semiconductor superlattices
Date of this Version
9-15-2012Citation
J. Appl. Phys. 112, 063714 (2012); http://dx.doi.org/10.1063/1.4754514
Abstract
Lanthanum strontium manganate (La0.67Sr0.33MnO3, i.e., LSMO)/lanthanum manganate (LaMnO3, i.e., LMO) perovskite oxide metal/semiconductor superlattices were investigated as a potential p-type thermoelectric material. Growth was performed using pulsed laser deposition to achieve epitaxial LSMO (metal)/LMO (p-type semiconductor) superlattices on (100)-strontium titanate (STO) substrates. The magnitude of the in-plane Seebeck coefficient of LSMO thin films (/K) is consistent with metallic behavior, while LMO thin films were p-type with a room temperature Seebeck coefficient of 140 mu V/K. Thermal conductivity measurements via the photo-acoustic (PA) technique showed that LSMO/LMO superlattices exhibit a room temperature cross-plane thermal conductivity (0.89 W/m.K) that is significantly lower than the thermal conductivity of individual thin films of either LSMO (1.60 W/m.K) or LMO (1.29 W/m.K). The lower thermal conductivity of LSMO/LMO superlattices may help overcome one of the major limitations of oxides as thermoelectrics. In addition to a low cross-plane thermal conductivity, a high ZT requires a high power factor (S-2 sigma). Cross-plane electrical transport measurements were carried out on cylindrical pillars etched in LSMO/LMO superlattices via inductively coupled plasma reactive ion etching. Cross-plane electrical resistivity data for LSMO/LMO superlattices showed a magnetic phase transition temperature (T-P) or metal-semiconductor transition at similar to 330 K, which is similar to 80K higher than the T-P observed for in-plane resistivity of LSMO, LMO, or LSMO/LMO thin films. The room temperature cross-plane resistivity (rho(c)) was found to be greater than the in-plane resistivity by about three orders of magnitude. The magnitude and temperature dependence of the cross-plane conductivity of LSMO/LMO superlattices suggests the presence of a barrier with the effective barrier height of similar to 300 meV. Although the magnitude of the cross-plane power factor is too low for thermoelectric applications by a factor of approximately 10(-4)-in part because the growth conditions chosen for this study yielded relatively high resistivity films-the temperature dependence of the resistivity and the potential for tuning the power factor by engineering strain, oxygen stoichiometry, and electronic band structure suggest that these epitaxial metal/semiconductor superlattices are deserving of further investigation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754514]
Discipline(s)
Nanoscience and Nanotechnology
Download
Comments
Copyright (2012) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in J. Appl. Phys. 112, 063714 (2012) and may be found at http://dx.doi.org/10.1063/1.4754514. The following article has been submitted to/accepted by Journal of Applied Physics. Copyright (2012) Pankaj Jha, Timothy D. Sands, Laura Cassels, Philip Jackson, Tela Favaloro, Benjamin Kirk, Joshua Zide, Xianfan Xu and Ali Shakouri. This article is distributed under a Creative Commons Attribution 3.0 Unported License.