| 摘要 |
PURPOSE:To increase the bonding strength of a substrate metal of a cathode and an alkaline earth metal oxide layer to be coated thereon, and obtain an electron emission characteristic stabilized for a long time even in the condition at a high density of current. CONSTITUTION:In an electron tube provided with a cathode, in which the surface of a substrate metal 2 is coated with an alkaline earth metal oxide layer 4, an upper layer 5, which is obtained by distributing a predetermined quantity of rare earth metal oxide in the alkaline earth metal oxide, is formed on the alkaline earth metal oxide layer 4. As the rare earth metal oxide of the upper layer 5 has nearly the same shape with carbonate to be used for the formation of the alkaline earth metal oxide and has a mean grain size close to the mean grain size of the carbonate. |
