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Electron Diffraction on Barium Titanate Crystals

Research by TEM within the Range of Phase Transition at 120°

Oct. 03, 2011
Fig. 1: Magnification of one of the spots on the surface of the negative.
Fig. 1: Magnification of one of the spots on the surface of the negative. more
Fig. 1: Magnification of one of the spots on the surface of the negative. Fig. 2: Photograph of the edge of a mosaic-like crystal of BaTiO3 with its diffraction pattern. Fig. 3: Diffraction pattern of a crystal near phase transition at 120°C. Fig. 4: Shot through the negative pattern during electron diffraction on BaTiO3 single crystals. Fig. 5: Traces of an impact by a cylindrical wave. The central spots in the small and the large ... Fig. 6: Further examples of collisions that accompany the electron diffraction on BaTiO3 single ... Fig. 7: Magnification of one of the spots on the surface of the negative. The central circle is of ... Fig. 8: Increased sedimentation of products of impurity from the negative developer on the spot. 

Apart from the domain structures that were discovered on BaTiO3 single crystals by means of TEM, there are a couple of unusual effects we know very little about. Some of these effects that require further research are transition structures, or optical radiation which accompanies the diffraction of electrons close to the temperature of phase transition as well as far below. Impact of neutrons or other heavy particles forms many spots on the surface of the negative (fig. 1.)

Introduction

The research enhanced by transmission electron microscopy (TEM) into ferro­electric domains of BaTiO3 single crystals [1, 2, 3], as well as into transitory structures within the range of phase transition [4] has had no influence on the theory of ferroelectricity, so far. The photographs of crystal surfaces and the diffraction patterns of the different ranges (fig. 2) can be sufficiently explained by the present theory of electron diffraction. In this article we shall present results of experiments on the anomalous absorption of electrons during electron diffraction on BaTiO3 single crystals at 50keV. The BaTiO3 single crystals were grown according to the Remeika method. The crystals were then corroded by ­phosphoric acid at temperatures of about 200°C until they reached their adequate thickness (300-500Å).

Phenomena Which Accompany Electron Diffraction

There are a couple of phenomena which accompany the electron diffraction on BaTiO3 single crystals. Among those phenomena is the Tscherenkow-radiation which appears far from phase transition [5] but also very close to it [6]. Secondly, an anomalous absorption of electrons can be observed during the diffraction of electrons [7]. The classic theory does not take these effects into account [5, 6, 7].

Another phenomenon that appears during the diffraction of electrons on ­BaTiO3 single crystals is the formation of extra-satellites when it comes close to phase transition (fig. 3). These additional spots form triangles and have a distribution of intensity that is different from the main spots arising from diffraction of electrons.

Optical Stereo Microscopy

We have examined the negative material with an optical stereo microscope in order to find further, more contrasted details.

First of all, several perforations which look very much like holes caused by laser beams, strike the eye [3]. It seems to be characteristic that these holes often form triangles similar to those formed by satellites (fig. 3). Holes in negative material have also been discovered in other research works [2]. It can be assumed that these extra-reflections (fig. 3) originate from very hot charges during the exposure to electronic radiation. The perforations of the negatives are likely to stem from coherent bundles (fig. 4).

High Contrast Details Formed by ­Impact of Heavy Particles

The intensity of such a bundle is not always sufficient for penetrating the negative material. In that event, traces of collision become visible at the surface of the negative (fig. 5). In some particular cases (fig. 6, 7) the central spots represent an ideal shape of a circle whereas the large circles were caused by the spreading heat during the collision. The effects mentioned above (fig. 4, 5, 6, 7) may be the result of cylindrical waves or of micro-particles [8]. It seems reasonable to assume, that the high-contrast details (fig. 5, 6, 7) were formed by impact of neutrons or other heavy particles. Similar structures were described in other publications [9]. During the impact of these particles on the film heat is allocated, extends on the negative surface and forms a stain of the fused substance of the film. The chemical and electric qualities of the film substance are changed in this area, this leads to the increased sedimentation of products of impurity from the negative developer on the spots (fig. 8).

Conclusion
If the escape of the particles was caused by shaking of a crystal lattice near the phase change, other investigation of these effects could find a practical use. Otherwise if the radiation was caused by the radioactive pollutions in the crystal, this work has a pure illustrative character.

References
[1] Tanaka M. and Honjo G.: Journal of the Physical Society of Japan 19, 954, (1964)
[2] Pfisterer H. and Liesk W.: Physikalische Blätter 24, 488 (1968)
[3] Matzeck C., et al.: Microscopy and Microanalysis 13 (Suppl 3), 370-371 (2007)
[4] Bursian E.W., et al.: Sov.Phys. Solid State, 19, 1108 (1977)
[5] Wall A.: Optik 90, 187 (1992)
[6] Wall A.: Microscopy and Microanalysis 13 (Suppl 3), 374-375 (2007)
[7] Wall A.: EMC 2008, Vol. 2: Materials Science, 583-584 (2008)
[8] Schrempp B. and Schrempp F.: Physikalische Blätter 41, 335 (1985)
[9] Medveczky L.: Solid Nuclear Track Detectors, 10th International Conference, 581-584 (1979)

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Keywords: Barium Titanate Single Crystals Electron Diffraction Phase Transition Transmission Electron Microscopy

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