Novel emitter materials, electrode assemblies amd lamps comprising the same are provided in which, in accordance with the invention, novel electrodes are provided having a lamp electrode structure, preferably including a hollow ferrule for sealing in a lamp to permit evacuation; an emitter material of the invention on at least one surface thereof, preferably on a protrusion attached to the hollow ferrule; a thermal isolator, preferably in the form of a low thermal conductivity wire or an incised or cut-out portion of the hollow ferrule body, for thermally isolating the protrusion from the ferrule to maintain a sufficiently high temperature for thermionic emission, and further comprising an emitter material requiring no in-lamp processing. The emitter materials are a mixed oxide of Ba, Sr and mixtures thereof with one or more of the metals from the series comprising Ta, Ti, Zr, Sc, Y, and La, are preferably selected from the group consisting of Ba.sub.4 Ta.sub.2 O.sub.9, Ba.sub.5 Ta.sub.4 O.sub.15, BaY.sub.2 O.sub.4, BaCeO.sub.3, Ba.sub.x Sr.sub.1-x Y.sub.2 O.sub.4, Ba.sub.2 TiO.sub.4, BaZrO.sub.3, Ba.sub.x Sr.sub.1-x TiO.sub.3, and Ba.sub.x Sr.sub.1-x ZrO.sub.3, wherein x ranges from a value of 0 to 1, and are most preferably one or more mixed oxides selected from the group consisting of Ba.sub.4 Ta.sub.2 O.sub.9, BaY.sub.2 O.sub.4, BaCeO.sub.3, Ba.sub.0.5 Sr.sub.0.5 Y.sub.2 O.sub.4, Ba.sub.0.75 Sr.sub.0.25 Y.sub.2 O.sub.4, Ba.sub.2 TiO.sub.4, BaZrO.sub.3, Ba.sub.0.5 Sr.sub.0.5 TiO.sub.3, and Ba.sub.0.5 Sr.sub.0.5 ZrO.sub.3.