Electron emission from ferroelectric cathodes is investigated, it is commonly suggested as an electron source for different applications due to its special characteristics such as high current density, easy treatment, and operation. In this experimental research, a lifetime of lead zirconate-titanate ceramic cathode with composition related to a ferroelectric phase was studied. The strong plasma emission from the cathode was excited in a nonreversal (nonswitching) mode by application of unipolar high stress. Severe damage to the cathodes was observed, especially in a high repetition rate. An upper limit of the lifetime of the ferroelectric cathode with plasma-induced emission was estimated at about ∼106 pulses of ∼200 ns each at ∼100 Hz repetition rate. Possible applications of the limited lifetime ferroelectric cathode are discussed.

Electron emission from ferroelectrics (FEE) is an unconventional electron emission effect. Methods of FEE excitation are quite different compared to classic electron emission from solids. Two kinds of FEE have been observed, “weak” and “strong.” “Weak” electron emission (current density 10−12–10−7 A/cm2) occurs from polar surfaces of ferroelectric materials in the ferroelectric phase only. A source of the electric field for “weak” FEE excitation is an uncompensated charge, generated by a deviation of macroscopic spontaneous polarization from its equilibrium state under a pyroelectric effect, piezoelectric effect, or polarization switching. The FEE is a tunneling emission current which screens uncompensated polarization charges. It is shown that the FEE is an effective tool for direct domain imaging and studies of electronic properties of ferroelectrics. “Strong” FEE, which is 10–12 orders of magnitude higher than “weak” FEE, achieves 100 A/cm2 and is plasma-assisted electron emission. Two modes of the surface flashover plasma formation followed by strong electron emission have been studied. The plasma of ferroelectric origin has been observed only in the ferroelectric phase and it is induced by polarization switching or a field-enforced phase transition, such as antiferroelectric–ferroelectric or relaxor–ferroelectric. The second mode of plasma is conventional surface flashover which may be initiated by a high voltage application in any phase from any dielectric, including ferroelectrics. In this review paper we consider numerous experimental results, as well as mechanisms of both types of electron emission from ferroelectrics. The main stress is placed on the material aspect in order to clarify the influence of ferroelectricity (ferroelectric phase transitions, polarization switching, etc.) on electron emission. Another aspect which is broadly discussed is the potential applications of these unconventional FEE emitters in various devices for development of high density FEE cathodes for microwave devices, as well as FEE converters of IR irradiation into visible light, x-ray imaging, FEE flat panel displays, etc.

A ferroelectric cathode is employed in a cyclotron-resonance maser (CRM). The CRM oscillator device operates at similar to 7 GHz, near the cutoff frequency of a hollow cylindrical cavity. The cathode is made of a PLZT 12/65/35 ceramic with high-dielectric constant (epsilon(r)similar to 4000). Electrons are extracted from the plasma excited on the cathode surface by similar to 1 kV short rise-time pulses. The use of ferroelectric cathodes may advance the microwave tube technology for various applications. (C) 1999 American Institute of Physics. [S0003-6951(99)03403-8].

It is shown that two quite different mechanisms may be responsible for surface plasma initiation at a polar surface of PLZT 7/65/35 ferroelectric ceramic. Priming electron emission required for surface flashover initiation may arise due to either field electron emission at triple junctions or electron emission caused by polarization reversal. In the former case neither polarization reversal nor ferroelectric state is required. In the latter case the surface plasma can be generated twice during the applied voltage pulse due to both forward polarization reversal and backswitching of ferroelectric domains. This leads to a much higher emitted electron charge compared with that caused by the polarization reversal. The experimental data enable us to conclude that, regardless of the initiation mechanism, strong electron emission from ferroelectric cathodes is a plasma-assisted effect.

It is shown that two quite different mechanisms may be responsible for surface plasma initiation at a polar surface of PLZT 7/65/35 ferroelectric ceramic. Priming electron emission required for surface flashover initiation may arise due to either field electron emission at triple junctions or electron emission caused by polarization reversal. In the former case neither polarization reversal nor ferroelectric state is required. In the latter case the surface plasma can be generated twice during the applied voltage pulse due to both forward polarization reversal and backswitching of ferroelectric domains. This leads to a much higher emitted electron charge compared with that caused by the polarization reversal. The experimental data enable us to conclude that, regardless of the initiation mechanism, strong electron emission from ferroelectric cathodes is a plasma-assisted effect.

A pulsed ferroelectric electron cathode with a current density of up to 45 A based on ceramic is presented. The experimental set-up for the cathode triggering allowed us to achieve a perveance of more than P and an energy spread in the generated electron beam as low as 100 eV (FWHM).

A flashover plasma has been induced by spontaneous polarization switching on a polar surface of the ferroelectric crystal triglycine sulphate (TGS). The effect has not been observed in the paraelectric phase. The threshold switching voltage for a surface flashover ignition was as low as 100 V for pulsed and ac voltage. A mechanism of plasma initiation on a ferroelectric surface is proposed. It is assumed that the plasma is ignited by electron emission initiated by polarization switching. Subsequent electron avalanching occurs as a result of the high potential gradient along the ferroelectric surface caused by inhomogeneous polarization switching. Electrons and ions with energies up to several hundreds of eV were been recorded due to a high surface potential of the switched ferroelectric.

A new mechanism of polarization switching and electron emission in ferroelectric cathodes is proposed. Surface flashover plasma of a ferroelectric origin was observed on a polar ferroelectric surface [D. Shur, G. Rosenman, and Ya. E. Krasik, Appl. Phys. Lett. 70, 574 (1997)]. Simultaneous measurements of switched charge and plasma density show that expanding surface plasma represents a dynamic switching electrode. Direct measurements of ion/electron emission currents and surface analysis implemented by different analytic tools indicate that electrons and ions from the surface plasma contribute to spontaneous polarization screening. The high energy of charged particles emitted from the surface plasma is ascribed to a high surface potential during polarization switching.

Strong pulsed electron emission has been observed from 12/65/35 lead lanthanum zirconate titanate ceramic composition in two different nonswitched phases at room temperature and at the temperature 100 degrees C. The electron emission parameters of this composition appear to be independent of phase for the two phases investigated. Fast photography acid direct observation show that the strong electron emission occurs from the surface discharge pfa;sma. The new experimental data make it possible to demonstrate the validity of the Child-Langmuir law for this electron emitter. A pulsed plasma lead lanthanum zirconate titanate ceramic cathode with burst frequency up to 100 KHz and collector current density up to 10 A/cm(2) is developed. (C) 1996 American Institute of Physics.

Pyroelectrically induced electron emission from different ferroelectric single crystals and ceramics is studied. It is observed that (Pb,La)(Zr,Ti)O3 ceramics generate rather low ferroelectric electron emission (FEE) current compared with single crystals such as triglycine sulphate and lithium niobate. Figures of merit for FEE cathodes in the pyroelectric excitation mode are derived. It is shown that a physical origin and consequently figures of merit are quite different for FEE cathodes and conventional field electron cathodes.

Ferroelectric electron emission observed under periodic spontaneous polarization switching is the basis for the development of a new type of flat panel display. Electron emission occurs from individually operated ferroelectric domains. It is shown that ferroelectric displays may be fabricated in ‘‘plane-to-plane’’ geometry which is not possible for field emission displays.

Pyroelectric properties of LiNbO3 crystals are studied by SEM. It is shown that various diffusion treatments of these crystals causing changes both of the domain configurations and crystal conductivity give rise to a strong variation of the pyroelectric potential.

Basic switching parameters (switching transient current, switching time, etc.) observed during electrical polarization reversal of undoped ferroelectric triglycine sulfate crystals with free surface are asymmetric. A comparison of the experimental data with the theoretical models of Fatuzzo [Phys. Rev. 127, 1999 (1962)], Pulvari, and Kuebler [J. Appl. Phys. 29, 1742 (1958)] shows that the classic models cannot to the fullest describe this type of polarization reversal. It is suggested that the asymmetric switching is caused by the difference in the field electron emission from a metal switching electrode and a ferroelectric crystal.

Pyroelectrically induced electron emission (EE) is studied from LiNbO3 crystals with a layered domain structure fabricated under various diffusion treatments. It is observed that the appearance of a thin oppositely polarized surface layer at the +C-surface suppresses EE. For bidomain configuration with equal thicknesses of the inverted and the original domains EE occurs from the boundary between two domains. It is proposed that a potential barrier for emitted electrons depends strongly on the spontaneous polarization direction at a free polar surface,

The basic property of ferroelectric crystals is switching of the direction of the macroscopic electric dipole moment under applying of an external electric field. Recently the polarization reversal effect without the external electric field has been discovered. It occurs under some treatments, namely, during proton-exchange. Ti,Rh-indiffusion in LiNbO3, out(in)-diffusion in LiNbO4, and LiTaO3, under Rb ionexchange and out(in)-diffusion at elevated temperature in KTiOPO4. The effect takes place at any polar surface and it is observed both far and near the Curie temperature. As a result a bidomain structure is formed. The diffusion-induced polarization reversal in ferroelectrics represents a new physical phenomenon and it is widely used in modern electronics and nonlinear optics. The studies of the effect are based on several traditional and new methods providing necessary data about the spontaneous polarization distribution and electrical parameters of these structures. In this paper, we review recent progress in the understanding of this phenomenon.

Ferroelectric electron emission is a novel type of electron emission from solids. It is observed under unconventional excitations of spontaneously polarized crystals (ferroelectrics) that made it possible to develop a new generation of non-conventional electron cathodes.

It is shown experimentally that the electron charge emitted from triglycine sulfate pulse ferroelectric cathodes can be as large as 129 μC/cm2. This charge considerably exceeds the measured value of spontaneous polarization, Ps=2.8 μC/cm2. A bipolar voltage is found to facilitate the appearance of the electron emission. It is proposed that the source of the emission current is the plasma of uncompleted surface discharges. This plasma is initiated at the metal-vacuum-dielectric triple points both by the field electron emission and the electron emission stimulated by polarization switching.

Our studies of piezoelectric properties of bidomain (‘‘head-to-head’’) Z-cut plates of LiNbO3 formed by diffusion treatment show that the spectrum of excited vibrations differs from that of monodomain crystals. We found that the length- and width-longitudinal vibrations are suppressed and bending vibrations appear to be maximal for an inverted layer thickness equal to one-half of the sample thickness. The amplitude of the fundamental frequency and its overtones for the thickness vibrations depend on the thickness of the inverted layer. A model explaining these properties is proposed.