Oxide cathode with rare earth addition

A cathode comprising a supporting body substantially comprising nickel and a layer of electron-emissive material provided on the body, the layer comprising barium oxide, at least one oxide selected from the group consisting of strontium oxide and calcium oxide and at least one rare earth metal, characterized in that the number of rare earth metal atoms which are provided by the at least one rare earth metal in the electron-emissive material, as a fraction of the number of barium atoms and atoms selected from the group consisting of strontium and calcium atoms provided by the at least one oxide selected from the group consisting of strontium oxide and calcium oxide in the electron-emissive material, is 10-500 ppm and in that the rare earth metal atoms provided by the at least one rare earth metal are distributed substantially uniformly in each particle of barium oxide and the at least one oxide selected from the group consisting of calcium oxide and strontium oxide present in at least the upper part of the layer of electron-emissive material.

A cathode comprising a supporting body substantially comprising nickel and a layer of electron-emissive material provided on the body, the layer comprising alkaline earth metal oxide, the alkaline earth metal oxide containing at least barium oxide and a rare earth metal, characterized in that the rare earth metal is present in such a concentration that the number of rare earth metal atoms provided by said rare earth metal in the electron-emissive material, as a fraction of the number of alkaline earth metal atoms in the electron-emissive material is 10-500 ppm and in that at least alkaline earth metal oxide particles present in the upper part of the layer of electron-emissive material comprise rare earth metal atoms whereby the rare earth metal atoms are distributed substantially uniformly.