无铅阴极的相变致电子发射研究

研究了最新无铅阴极钛酸铋钠(Na1 2Bi1.2TiO3，NBT)基铁电陶瓷的电子发射性能和电子发射的机理。采用常规陶瓷工艺制备了发射阴极样品，并在阴极上施加高达15kV的激励脉冲，获得了20A／cm^2的最大发射电流密度。在施加激励电压的同时观察到3个发射电流脉冲峰值，该现象不同于其他的阴极。通过测试NBT基铁电陶瓷的相变性能，修正了得到公认的快极化反转致电子发射理论，提出相变致电子发射理论公式，合理解释了该新型无铅NBT基阴极的电子发射3个峰现象，说明了电子发射不仅可以由快极化反转产生，也可以由相变导致的极化变化产生。

STUDY OF ELECTRON EMISSION INDUCED BY PHASE TRANSITION FROM LEAD FREE CATHODES

The electron emission properties of sodium bismuth titanate (Na_(1/2) Bi_(1/2) TiO_3, NBT) base ferroelectric ceramic and the mechanism of electron emission in this novel cathode were studied. The NBT based cathodes were prepared by the conventional ceramic technique and high pulses up to 15 kV were exerted on the cathodes. The emission current density of 20 A/cm~2 is obtained and three peaks of current are observed, which is different to other ferroelectric cathodes during the period of excited field. The phase transition properties of NBT ferroelectrics were tested and the phase transition induced electron emission theory based on fast polarization switch theory was brought up. This amendment well explains the observed three peeks of emitted current and shows that electron emission can be not only produced by polarization switch but also produced by other kind of polarization change such as phase transition in NBT based ferroelectrics.