Electron conduction associated with the chemical transport of reducing elements in oxide cathode for CRT's application

In the present work, the formation of compounds associated to the diffusion of reducing elements (Mg, Al and W) to the Ni cap surface of oxide cathode has been studied by a new method. This method used two cathodes, one of them is coated and the other is uncoated, to be in an attach-contact mounted in a dummy tube. Different analytical techniques were used for this study: scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and I/V electrical measurements. After oxide cathode plus decomposited and activated, Al and Mg doping elements take place during heating to 810 degrees C (Ni-Br) under a rich controlled Ba/SrO atmosphere through an acceleration life test. It is shown that the chemical transport occurs mainly by a grain boundary mechanism with significant pile-up of Mg compounds. Al and W show a superficial concentrations and distribution. The dc electrical characteristic shows very strong rectifying behaviour through the M-S junction due to the I/V curves, particularly after 144 h acceleration life time. The characteristics are found to be reversible and reproducible, and viewed a rectification ratio (r) of 100. The calculated ideality factor shows a value of n = 9.6, which is evidenced to the tunnelling conduction. The theoretical calculation shows that the interface thickness grows to (similar to 6 mu m) after accelerated the cathode to 1896 h. (c) 2005 Elsevier B.V. All rights reserved.