P-type perovskite oxide metal/semiconductor superlattices for thermoelectric generators
Abstract
Metal/semiconductor superlattices with cross-plane transport offer a novel approach towards improving the thermoelectric figure of merit (ZT) over conventional thermoelectric materials operating at high temperatures 800–1000K. The perovskite oxides are a promising materials system for these metal/semiconductor superlattices due to their diverse range of properties, which allows tuning of the intertwined thermoelectric properties. Lanthanum Strontium Manganate (LSMO)/Lanthanum Manganate (LMO) perovskite oxide metal/semiconductor superlattices were investigated as a potential p-type thermoelectric generator element operating at 800–1000K. Epitaxial superlattices of LSMO (metal) and LMO (p-type semiconductor) were deposited on Strontium Titanate (STO) substrates using pulsed laser deposition in an oxygen ambient. Individual films and superlattice materials were characterized by high-resolution x-ray diffraction, reciprocal space mapping and transmission electron microscopy. LSMO/LMO superlattices exhibited a room temperature thermal conductivity (0.89 W/m˙K) lower than either LSMO (1.60 W/m˙K) or LMO (1.29 W/m˙K) thin films individually. In addition to a low thermal conductivity, a high ZT requires a high power factor, the product of the electrical conductivity and the square of the Seebeck coefficient. In an effort to perform cross-plane electrical transport measurements, an LSMO/LMO superlattice etch recipe was developed using reactive ion etching. A series of micro-fabrication steps resulted in cylindrical pillars of the superlattice. Cross-plane IV- T measurements yielded preliminary data for cross-plane conductivity, the Seebeck coefficient and the Schottky barrier height. The measured cross-plane conductivities of LSMO/LMO superlattices suggest a combination of magnetic transitions and thermionic behavior. The novel approach of using p-type perovskite oxide superlattices of LSMO/LMO using cross-plane transport has the potential to provide a new high temperature thermoelectric material system.
Degree
M.S.E.C.E.
Advisors
Sands, Purdue University.
Subject Area
Electrical engineering|Nanoscience|Nanotechnology
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