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To improve the thermionic emission performance of the rare-earth refractory yttrium salt cathode used in the magnetron, the influence of Sc2O3 doping on its thermionic emission properties was explored. Cathodes were fabricated by incorporating different weight percentages of Sc2O3 into the rare-earth refractory yttrium salt matrix, and their thermionic emission properties were systematically evaluated. The experimental findings revealed that the doping of Sc2O3 significantly enhances the thermionic emission capability of the cathode. Notably, a doping concentration of 3wt% Sc2O3 yielded the most pronounced improvement in emission performance. The 3wt% Sc2O3-doped cathode could achieve a thermionic emission current density of 3.85A/cm2 under a 300 V anode voltage at 1600℃. In contrast, the undoped cathode supplied a current density of merely 1.66A/cm2 under identical conditions, demonstrating a 132% enhancement in thermionic emission efficiency with 3wt% Sc2O3 doping. Utilizing the Richardson line method coupled with data-fitting algorithms, the absolute zero work functions for undoped and Sc2O3-doped cathodes (3wt%, 7wt%, and 11wt%) were determined to be 1.42, 0.93, 0.98, and 1.11 eV, respectively. Longevity assessments indicated that the 3wt% Sc2O3-doped cathode had been stable for over 4200 hours without significant degradation under an initial load of 0.5 A/cm2 at 1400℃. Finaly, those cathodes had been analyzed by the XRD, SEM, EDS, AES respectively. The analysis results showed that during thermionic emission testing, the Sc2O3 and Y2Hf2O7 had undergone substitutional solid solution reactions, forming the ScxY(2-x)Hf2O[7+(3/2)x] solid solution. This process induced lattice distortion in the Y2Hf2O7, placing it in a high-energy state and thereby reducing the work function on the cathode’s surface. Concurrently, Sc from Sc2O3 displaced Y within the Y2Hf2O7 unit cells, with the displaced Y existing in a metallic form, which enhanced the electrical conductivity of the cathode's surface. Additionally, the ScxY(2-x)Hf2O[7+(3/2)x] solid solution generated a substantial number of Vo2+ oxygen vacancies and free electrons, further augmenting surface conductivity. Collectively, these mechanisms contributed to a marked enhancement in the cathode's thermionic emission capacity.
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Keywords:
- Sc2O3 doping /
- thermionic emission /
- emission mechanism /
- magnetron
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