The electric charge transport in titania–alumina composite cold cathodes made using atmospheric plasma spraying and laser engraving

Titania composite layers made by atmospheric plasma spraying (APS) technique and laser engraving have been investigated as field electron emitters (Atmospheric Plasma Sprayed and Laser Engraved APSLE cathodes). Emission characteristics of the emitters made of pure TiO2 and those made of Al2O3 + 13 wt.% TiO2 appeared to be comparable with the conventional emitters made of nano-crystal diamond or diamond like materials. The paper presents the results of the mechanisms of the electrical charge transport through the bulk of the APSLE composite layers. The electrical properties of tested layers were determined by means of impedance spectroscopy (IS).Two equivalent electrical models based on IS measurements have been proposed. Behavior of these models reflects the electrophysical phenomena in the APSLE composite layers. Analysis of these models indicates that the conducting paths in the APSLE layers are formed by defect rutile and titanium suboxides (Magneli phases). The dielectric bead consists of rutile (TiO2), corundum (Al2O3) and spinel (Al2TiO5). Spinel and traces of organic impurities present in the Al2O3 + 40% TiO2 composite may completely lock the charge carrier transport in the bulk of material. It is probable that the organic impurities could have been a catalyzer of the spinel formation. There is an interesting result of plasma spraying Al2O3—40 wt.% TiO2 powders on sprayed coatings. The electric properties of the coating depend upon the powder manufacturing method.

► After [27] Al2O3 + 40 wt.% TiO2 should emit better than the one with 13 wt.% TiO2.
► We expected also that more dense laser engraved surfaces will be more emissive.
► The organic phases in APSL layers were undetectable by structural investigations.
► The IS can explain the influence of the complex structure on charge transport.