Thermomigration and Soret effect in Na_xCoO₂ as thermoelectric material: Preparation and characterization of sodium cobaltate thin films

Abstract

Sodium cobaltate (NaxCoO2, 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., Cu2 – xSe). 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 NaxCoO2 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 about D˜Na = 5 × 10−4 cm2 s−1.

Emerging Thermal Technology Enabled Augmented Reality

“…[ 160b,165 ] In the case of electrolyte, sodium, or potassium ions contained electrolytes showed the capacitive performance by the Soret effect. [ 165,166 ] Recently, proton diffusion of the ionic thermoelectric device has been introduced. Generally, the sulfonic acid group contained polymer provides proton transport in the polymer matrix.…”

CO2—H2O Capture and Cyclability on Sodium Cobaltate at Low Temperatures (30–80 °C): Experimental and Theoretical Analysis

“…On the other hand, sodium cobaltate (Na x CoO 2 ) compounds are layered‐structural materials used in thermoelectric applications, where their structural and transportation properties have been mainly studied . Recently, this material has been probed as a possible CO 2 captor, showing that it is able to chemisorb up to , between 150 and 740 °C, producing Na 2 CO 3 and different cobalt oxides.…”