The conductivity of oxide cathodes. Part 9: Thermo-electric power

The thermo-electric power of an oxide cathode has been examined recently by J. R. Young, who finds it to be a complex function of temperature, dependent on the dual nature of oxide-cathode conductivity. By an experimental artifice the present authors show that an apparently complex form of behaviour is, in fact, the result of the superposition of two quite simple phenomena. Two parallel-acting thermo-electric power functions are involved, and each of these is invariant with temperature and temperature gradient. The two functions are physically separated and each is measured over an appropriate temperature range. The larger function, of magnitude 2.0 ¿ 3.0mV/degC, is associated with the vacuum movement of electrons through the hollow pores of the oxide matrix; the smaller one, of magnitude 0.5mV/degC, occurs in the chains of contiguous solid particles of the matrix. Owing to the parallel connection and inequality of these functions, it is concluded that a temperature gradient through an oxide matrix leads to a continuous circulation of current, vacuum-wise in one direction and solid-wise in the other. Since the larger function is essentially one involving thermionic emission of electrons in a vacuum, it can be satisfactorily explained in terms of Richardson´s law.