A novel Y<sub>2</sub>Hf<sub>2</sub>O<sub>7</sub> ceramic cathode applied to high power magnetron tube

Abstract

Nowadays, the output power and lifetime of a single magnetron are far from the requirements of industrial applications. So the new materials and methods are urgently needed to enhance the output power and prolong the lifetime of the magnetron. As the heart of a magnetron, cathode, whose quality directly affects the output power and lifetime of the magnetron, plays an important role. In order to enhance the output power and prolong the lifetime of the high power magnetron, a method of doping rare earth oxide Y<sub>2</sub>O<sub>3</sub> into transition metal oxide HfO<sub>2</sub> is used to prepare Y<sub>2</sub>Hf<sub>2</sub>O<sub>7</sub> ceramic cathode. The thermionic emission and lifetime characteristics of the Y<sub>2</sub>Hf<sub>2</sub>O<sub>7</sub> cathode are measured. The results show that the cathode can provide 0.15, 0.2, 0.5, 1.1, 1.8, 2.5, 3.5 A/cm<sup>2</sup> current density for the space charge limitation at 1300, 1350, 1400, 1450, 1500, 1550, 1600 ℃br under 300 V anode voltage, respectively. Absolute zero work function of the cathode is only 1.26 eV obtained by the Richardson line method. The effective work function of the cathode is 3.10, 3.15, 3.21, 3.26 eV obtained by the Richardson-Dushman formula at 1450, 1500, 1550, 1600 ℃br respectively. The lifetime of the cathode is more than 4000 h under an initial load of 0.5 A/cm<sup>2</sup> at 1400 ℃br, the lifetime which is much longer than the 2000 h average life span for the 2450 MHz continuous wave magnetron cathode used in production. Finally, the molecular structure, surface microstructure, element composition and content of the Y<sub>2</sub>Hf<sub>2</sub>O<sub>7</sub> ceramic cathode are analyzed by the X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, Auger electron spectroscopy with argon ion etching respectively. The analysis results show that the single Y<sub>2</sub>Hf<sub>2</sub>O<sub>7</sub> phase forms under the high sintering temperature. When the Y<sup>3+</sup> valence Y<sub>2</sub>O<sub>3</sub> is doped into the Hf<sup>4+</sup> valence HfO<sub>2</sub>, the substitutional solid solution will form. An oxygen vacancy is generated in the lattice, thus maintaining the electrical neutrality of the Y<sub>2</sub>Hf<sub>2</sub>O<sub>7</sub> lattice. During the cathode activating, aging, and thermally testing, the oxygen vacancy is generated fast. The more the obtained oxygen vacancies, the higher the conductivity of the cathode surface will be. Besides, due to the improvement of the electro-conductivity thus enhancing the thermionic emission capability of the cathode, the work function of the cathode can be reduced.