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Thermomigration and Soret effect in Na x CoO 2 as thermoelectric material: Preparation and characterization of sodium cobaltate thin films
Author(s) -
Schneider Christian,
Schichtel Patrick,
Mogwitz Boris,
Straubinger Rainer,
Beyer Andreas,
Rohnke Marcus,
Volz Kerstin,
Janek Jürgen
Publication year - 2016
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201532725
Subject(s) - thermoelectric effect , materials science , analytical chemistry (journal) , thermophoresis , stoichiometry , seebeck coefficient , sapphire , thermoelectric materials , thin film , thermodynamics , chemistry , nanotechnology , nanoparticle , laser , nanofluid , physics , chromatography , optics
Sodium cobaltate (Na x CoO 2 , NCO) is a model type thermoelectric material for high temperature applications, which is representative for the class of non‐stoichiometric and mixed ion‐electron conducting thermoelectrics (e.g., Cu 2 – x Se). The present study deals with the kinetic instability of the originally homogeneous chemical composition when a temperature gradient is applied – a common situation in thermoelectric materials with a mobile component (element), but rarely considered in thermoelectric materials research so far. In order to investigate a well reproducible system, highly epitaxial thin films of Na x CoO 2 with an atmosphere protective capping layer of alumina are prepared via pulsed laser deposition on sapphire (001) and lanthanum aluminate (111). A self‐designed non‐isothermal set‐up allows the precise determination of the heat of transport for mobile sodium as 8.3 kJ mol −1 and, therefore, the quantification of thermodiffusion (i.e., the Ludwig‐Soret effect in the stationary state). The experiments also allow to estimate the chemical diffusion coefficient of sodium at 422 K as aboutD ˜N a = 5 × 10 −4 cm 2 s −1 .