Study of Nanostructure Inclusion Effects on the Thermoelectric Behavior of Ca 3 Co 4 O 9 Thin Films Grown by Pulsed Lase
- PDF / 456,521 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 27 Downloads / 164 Views
1267-DD10-14
Study of Nanostructure Inclusion Effects on the Thermoelectric Behavior of Ca3Co4O9 Thin Films Grown by Pulsed Laser Deposition Evan L. Thomas1, Xueyan Song2, Yonggao Yan3, Joshua Martin3, Winnie Wong-Ng3, Margaret Ratcliff4 and Paul N. Barnes5 1
Metals and Ceramics Division, University of Dayton Research Institute, Dayton, OH 454690073, U.S.A. 2 Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV 26506-6106, U.S.A. 3 Ceramics Division, MSEL, National Institute of Standards and Technology, Gaithersburg, MD 20899-8520, U.S.A. 4 Mechanical Engineering Department, University of Dayton, Dayton, OH 45469, U.S.A. 5 Propulsion Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433, U.S.A. ABSTRACT The influence of incorporating nanoparticulate additions into Ca3Co4O9 (CCO) thin films prepared by pulsed laser deposition using composite targets of CCO and CCO + 3wt% BaZrO3 (BZO) on Si and LaAlO3 substrates is investigated. X-ray data and high-resolution scanning electron microscopy reveal preferred c-axis orientation of the films deposited on Si substrates with the formation of nanoparticles between ~ 10 – 50 nm. Preliminary thermoelectric behavior shows an enhancement of the power factor α2/ρ at room temperature. The microstructure and thermoelectric behavior of the CCO films are compared to the BZO-doped films. INTRODUCTION Thermoelectric (TE) materials are capable of directly converting thermal energy into electrical energy and vice versa, and are considered clean energy converters [1]. However, for more practical use in applications, the conversion efficiency of TE materials stands to be increased, and is governed by a figure-of-merit, defined as zT = α2T/ρκ where α, T, ρ, and κ are Seebeck coefficient, absolute temperature, electrical resistivity and thermal conductivity, respectively. Some of the latest efforts towards increasing the efficiency of TE materials, particularly for thin film samples, have involved employing fabrication methods to decrease thermal conductivity through quantum confinement effects, lattice mismatching, and purposefully introducing structural defects. The misfit-layered cobaltite, Ca3Co4O9+δ (CCO) [2], owes its recent attraction as a potential low-cost TE material candidate to its large α, low ρ, and high thermal and chemical stability at high temperatures in air. The zT value for a single crystalline CCO sample reached 0.8 at 1000 K [3]. The crystal structure of CCO can be described as having a 2D structural character with triple NaCl-type Ca2CoO3 layers and single CdI2-type CoO2 layers that are alternately stacked, thus making it highly anisotropic. The Ca2CoO3 layers, as well as the misfit interface, serve as phonon scattering regions to achieve low thermal conductivity; meanwhile, the CoO2 layers (nanosheets), which possess a strongly correlated electron system, serve as electronic transport layers [3]. The crystal structure of CCO is closely related to that of
Bi2Sr2Co2Oy [4], another misfit-layered oxide, which
Data Loading...
