Formation of an interface layer in thermionic oxide cathodes for CRT applications

Scanning electron microscopic techniques were employed to study the surface morphological changes of oxide cathodes and nickel caps as a result of cathode activation extending over periods of 1-12 h. Elemental analysis of barium, strontium, tungsten, magnesium and aluminium was performed using energy dispersion x-ray spectroscopy. An abrupt change was observed after activation longer than 3 h. Conduction through well activated cathode assemblies was found to be due to intergranular electron tunnelling at low temperatures (T less than or equal to 500 K), while trapping and detrapping at grain boundaries becomes the dominant mechanism at high temperatures (T greater than or equal to 500 K). The contribution of the interfacial layer to conductivity was found to be significant for cathodes activated for smaller periods.