Perovskites as Ultralow Work Function Cathode Materials
Lower work function and more stable barium adsorption than existing technologies (e.g., tungsten or scandate surfaces) Potential for significantly extended cathode lifetime and higher electron emission levels
SrVO3 (with or without Ba doping) for ultralong lifetime, highly emissive cathode materialThermionic emission technologiesHigh power vacuum electronic devicesHigh power microwave components and systems
Electron emission cathode materials are found in high power electron beam devices used in defense, scientific research and communications applications as well as thermionic energy conversion technologies. Suitable electron source materials desirably exhibit a low work function, stability at high temperatures, and sufficient conductivity to sustain the desired emission current.Leading thermionic electronic emitters composed of refractory metals like tungsten – while stable and good conductors – must be coated with an oxide to lower the work function. These coatings are volatile and degrade over time, limiting the lifetime and efficiency of devices. Alternatively, perovskite materials are of interest because they possess desirably low work functions and may eliminate the need for a volatile surface layer. Determining the work function values for perovskites is essential for applications involving electron transport at interfaces or surfaces, including solar cells, electrocatalysts, conducting oxide electronics, Schottky barriers and vacuum electron emitters as well as thermionic energy conversion.Using high-throughput computing and informatics to screen thousands of candidates, UW–Madison researchers have identified a perovskite oxide, SrVO3, with a lower predicted work function than current state-of-the-art cathodes. SrVO3 exhibited one of the lowest calculated work functions (1.86 eV) out of 18 perovskite materials investigated (~ 40 compositionally distinct surfaces). Non-volatile barium doping was used to further lower the work function (1.07 eV) and was more stable than on tungsten or scandium surfaces, indicating that Ba will reside on SrVO3 orders of magnitude longer than on other widely explored thermionic cathode material surfaces.
Read a news story about this technology. http://news.wisc.edu/new-material-picked-by-computers-could-boost-power-of-vacuum-electronics/ For information about perovskite-based cathodes for solid oxide fuel cells and related technologies, see WARF reference number P160222US01.
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