R. Le Bihan

Study of ferroelectric and ferroelastic domain structures by scanning electron microscopy

Abstract At the beginning we present a review of the historical development of first observations of domain structures in ferroelectric and ferroelastic crystals with a SEM. A theory of the charging mechanism of an insulating sample bombarded by an electron beam gives an interpretation of experimental observations of ferroelectric crystals. This model is studied in order to give a guide to accomplish experiments and to interpret the observations of domains. A model of formation of the contrast between ferroelectric domains is presented. Visualization of domains and results obtained with unmetallized ferroelectric and ferroelastic crystals (TGS, BaTiO3, GASH, PbHPO4, LAS, etc.) are presented. The influence of the temperature and some other parameters on the domain structures is studied and their modifications at the ferroelectric-ferroelastic and ferroelectric-paraelectric phase transitions are also mentioned. Results obtained by the scanning electron decoration technique (SEDT) are presented.

Preparation of multi-coating PZT thick films by sol–gel method onto stainless steel substrates

PbZr0.45Ti0.55O3 ferroelectric films have been prepared by sol–gel method, using alkoxide precursor compounds and multi-layer technique. The gel films were deposited by spin-coating onto stainless steel substrates. In order to obtain crystallization in the perovskite phase, the samples were annealed at 600–700°C for 1 min. The dependence of the electric properties on the heat-treatment temperature is studied, and the coercive electric field as a function of the material thickness is determined. By SEM photography, the microstructure of the films could be shown to be homogeneous.

Barkhausen pulses and electron emission from 9.4/65/35 PLZT ceramics

Weak and strong electron emission from 9.4/65/35 PLZT ceramic into vacuum, excited by 50 Hz ac electric field, was observed. Two different emission processes, i) a tunnel electron emission at weak current density level and ii) a plasma-induced field emission at strong one, are evidenced and discussed. A control of the weak electron emission process seems to be possible contrary to the strong one.

Study of the surface of ferroelectric crystals with the scanning electron microscope

Abstract A method is reviewed for observing insulating samples in the scanning electron microscope without excessive specimen charging. In this way antiparallel domains may be directly observed without modification of the sample. The scanning electron microscope operating in the back-scattered electron mode reveals topography, and operation in the secondary electron mode at low voltage reveals surface potential variation. We have observed antiparallel domains on T.G.S., these domains disappear above the Curie point. The same method applied to BaTiO3 crystals reveals a ferroelectric surface layer, which has a domain structure different from the bulk and persists above the Curie point. KD2P and conducting WO3 crystals have also been studied.

Electron emission from ferroelectric crystals of different thickness

Abstract Electron emission from the surface of ferroelectrics TGS crystals and PZT ceramics is investigated for thickness from 6 μm to 1 mm. Study of electron emission distribution in time from Triglycine Sulfate (TGS) crystals of different thickness have been investigated. The correlation in time between emitted and switching currents and applied electric voltage is experimentally studied. It was shown that the electron emission occurs when the negative polarization charges appear at the emitting surface. An emitted current density up to 20 A/cm2 have been measured without inducing discharge. Interpretation of the results by considering the evolution of the domain switching, thickness of the samples and geometry of the electrodes have been realized. Electron emission from PZT ferroelectric thin films of 6.3 μm thickness is presented.

Electron emission from pulled BaTiO3 single crystals

Abstract Electron emission induced by the reversal of polarization in BaTiO 3 crystals grown by pulling method have been investigated in the 370–410 K temperature range. The electrons are emitted mainly during every second half-period of the electric a.c. switching field. Anomalies of the temperature dependences of the electron emission intensity at about 10 K below T c and at T c have been observed. The possible mechanism of this electron emission is discussed.

Surface study of ferroelectric domains on G. A. S. H. single crystals by scanning electron microscopy and Auger electron spectroscopy

Abstract The domain structure of G. A. S. H. single crystals is investigated by scanning electron microscopy without metallization of the surface of the crystal. In the middle of the surface, hexagonal domain corresponding to a potential variation is observed. Outside of this zone, ferroelectric domains of different shapes are observed, these antiparallel domains correspond to a surface potential variation and their contrast varies versus the accelerating voltage of the primary electrons as for T. G. S. The conditions for analyze the surface of G. A. S. H. crystal by Auger electron spectroscopy are obtained. A difference of sulfur and oxygen concentration between outside and inside of hexagonal domain is presented.

Study of ferroelectric domains structure on TGS crystals doped with L-α alanine

Abstract The domain structure of T.G.S. crystals doped with L-α alanine is investigated by scanning electron microscopy without metallization of the observed surface. Big zones observed in these crystals have, versus the voltage applied to the primary electron beam, a different contrast evolution from that we can observe for pure T. G. S. crystals. For domains obtained after heating the crystals above the Curie point, the evolution of the contrast observed for the ferroelectric domains is the same as for the ferroelectric domains of pure T.G.S. crystals and the shape of these domains is also lenticular.

Electron emission spectra from lead zirconate titanate ferroelectric films on stainless-steel substrates

Emission of electrons from lead zirconate titanate films was measured using excitation voltage pulses of different waveforms. Time-resolved measurements of the emission, voltage, and circuit current were conducted simultaneously. Electron emission spectra excited by a sine-wave voltage exhibited two distinguishable peaks arising every second half period of the applied voltage. Electron emission was also induced by film excitation with either square-wave voltage below coercive field, or unipolar pulses of appropriate polarity. The peculiarities of the emission are considered in terms of reversal of both induced (dielectric) and spontaneous (ferroelectric) polarization. Excitation of the electron emission in the “inversion of induced charge” mode seems to eliminate problems associated with reversal of spontaneous polarization as fatigue and necessity of resetting.

Study of lithium niobate with periodically reversed domains

Abstract Periodical domain structure on various surfaces of LiNbO3 crystals doped with Mg and Y or Dy was studied by scanning electron microscopy (SEM) and optical microscopy. A bright contrast of domain boundaries on both surfaces with P, lying in the plane (X-face) and on surfaces nearly normal to Ps was observed by SEM in the secondary electron emission mode. The domain structure periodicity of 5.5 μm was found on the X-face, whereas the domain periodicity of about 2.8 μm is visible on the surface nearly perpendicular to P. The second and third harmonic generation conditions were discussed.