Investigation of electron emission from bulk (Pb,La)(Zr,Ti)O/sub 3/ ferroelectric ceramics

Improvements in cathode technology represent one means of enhancing high power microwave tube performance. Of particular interest are low temperature cathodes which provide high current density electron beams. Our research focuses on the application of ferroelectric materials as an electron source. We are investigating two competing theories to explain the mechanism of emission from the material. The first method invokes a large charge imbalance induced by rapidly changing the polarization of the material. This charge imbalance accelerates screening charges (electrons) into the A-K gap. The second theory stipulates that an intense electric field at the periphery of the grid electrode vaporizes metallic protrusions of the grid. These explosions provide carriers as well as neutralize the space charge of the cathode. Experiments are conducted using a demountable high vacuum triode with bulk (300 /spl mu/m -1 cm) (Pb,La)(Zr,Ti)O/sub 3/ (PLZT). The ferroelectric PLZT samples under test are gridded with an evaporated gold film which is patterned with circular apertures. This grid is excited by a solid state driver which erects a field of 15 kV/cm in about 1 /spl mu/s. A DC bias voltage is used to reset the polarization of the material after each shot. Preliminary results indicate that this reset voltage greatly enhances the reliability of the electron emission. A DC voltage (up to +/-20 kV) applied to the anode accelerates any carriers liberated from the material. Hysteresis measurements are also conducted in situ to determine the dielectric properties of the candidate materials. Preliminary results of these experiments are presented.<>