Displacement and emission currents from PLZT 8/65/35 and 4/95/5 excited by a negative voltage pulse at the rear electrode

Abstract

It is shown that non-prepoled PLZT ceramics, both in ferroelectric and antiferroelectric phase, emit intense current bursts when a negative exciting voltage is applied to the rear surface of the cathode. The spontaneous polarization induced in the bulk by applying the field through the cathode disk, creates a sheet of negative charge on the diode boundary of the ferroelectric. This, in turn, induces such a high electric field at the diode dielectric surface that electrons are ejected out from the ceramic surface into the vacuum. The coherent behaviour of the displacement and emitted current shows clearly that the emission is due to a variation of spontaneous polarization. A second effect generated by the application of the high voltage pulse at the rear side is the formation of a surface plasma. 1-IntroductionA cathode composed by a ferroelectric disk sandwiched by a uniform electrode at the rear surface (RE) and a gridded electrode at the diode side (DE), emits high current pulses when properly excited by a fast electric field. At CERN experiments [1-3], the exciting field was directed from the front emitting surface of the cathode disk to the rear surface (negative excitation), whilst it was opposite in other experiments (positive excitation) [4][5][6][7]. In a previous paper [8] we have presented some results for the case of positive excitation, in this paper we present experimental results and the relative discussion for the case of negative excitation. We have studied the behaviour with and without an accelerating field through the gap of the diode, with the aim of selecting the energetic electrons from the rest and so to single out the ferroelectric effect from the metal-dielectric discharge effect. The samples in our experiments where not prepoled, contrary to experiments of ref.

Features and technology of ferroelectric electron emission

“…The strong electrically-induced emission from FE samples covered with metallic grid electrodes is very efficient, but weak FE emission has also been observed from a bare FE surface without any electrode or conducting material (for example, [3,5,26]). The latter type of electron emission cannot be induced with any of the alternative emission methods [14][15][16][17][18][19][20][21][22] using reverse field excitation, which rely on the field emission of electrons from the FE-metal interfaces of the GE grid electrode [27].…”

Impedance spectroscopy of (Pb0.98La0.02)(Zr0.95Ti0.05)O3(PLZT-2/95/5) ceramics above ferroelectric phase transition temperatures

“…Dielectric constant displays a slightly discontinuous drop at T L and a sharp peak at T U [18][19][20][21]. The AFE-FE phase transition point are shifted downwards with increasing La content (0.5oxo5%) .…”

“…However, the Pb 1Àx La x (Zr 1Ày Ti y ) 1Àx/4 O 3 , PLZT-x/100Ày/y, is a member of the perovskitetype oxide materials [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. The most typical properties of lead ziconate-titanate lantaniumdoped (PLZT) ceramics with Pb/La ratios (0oxo5%) and Zr/Ti ratios close to 95/5 are strong diffuse antiferroelectric-ferroelectric (AFE-FE) phase transition, exceptionally big thermal hysteresis, and a wide temperature range in which the AFE and FE phases coexist [18][19][20][21][22][23].…”

“…The most typical properties of lead ziconate-titanate lantaniumdoped (PLZT) ceramics with Pb/La ratios (0oxo5%) and Zr/Ti ratios close to 95/5 are strong diffuse antiferroelectric-ferroelectric (AFE-FE) phase transition, exceptionally big thermal hysteresis, and a wide temperature range in which the AFE and FE phases coexist [18][19][20][21][22][23].…”

Phase Transition Dielectric Anomaly of PLZT Ceramic in the Temperature Range of 30–350°C

“…5-8) The AFE-FE phase transition point are shifted downwards with increasing La content (0:5 < x < 5%). [5][6][7][8][9][10] Handerek et al 9) reported dielectric, pyroelectric, and thermally stimulated depolarization current investigations for PLZT x/95/5 ceramics for 0:5 < x < 4:0%. They observed relaxor like dielectric dispersion (10 Hz-10 4 Hz) at T U , and attributed this anomaly behavior to space-charge-induced polarization by mobile ionic defects.…”