Yarygin V.I., Тulin S.M.
A.I. Leypunsky Institute for Physics and Power Engineering, Obninsk, Russia
The article discusses the experimental results
of a comprehensive research of polycrystalline niobium electrodes in a laboratory
thermoemission thermal-to-electrical converter (TIC), modified by large-dose
implantation of oxygen ions (fluence ~1018 ion/cm2). It
was found by the methods of complex analysis that the activation annealing of
the Nbimp reference sample/TIC electrodes causes changes in the crystallographic structure of the Nbimp
electrodes with the formation on the emitter and collector surface of TICs
(polycrystalline in the initial state) of a stable electronic system Nb-O of
the type Nb6O suboxide with coarse-grained texture (110) with a
grain size of 30–100 microns and a
depth of oxygen up to 500–700
angstroms. The oxygen concentration on the surface of Nbimp
electrodes is 4–5 at. %, which is
an order of magnitude higher than the natural content of dissolved oxygen in
the initial polycrystalline niobium. Thermionic measurements in a laboratory
TIC established that the modification of Nbimp electrodes causes a
significant improvement in the emission-adsorption characteristics of TIC with
an Nbimp – Nbimp
electrode pair.
Within the framework
of a consistent physical model, the article examines the relationship between
the properties of modified Nbimp electrodes with a highly efficient
process of low-temperature thermionic conversion with an attractive barrier
index efficiency (2±0.06 eV) and electrode efficiency ~11% (at an emitter temperature ~1600
K).
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