Study of the ferroelectric phase transition of TlGaSe2 by dielectric,calorimetric, infrared and X-ray diffraction measurements |
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Authors: | H D Hochheimer E Gmelin W Bauhofer Ch von Schnering-Schwarz H G von Schnering J Ihringer W Appel |
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Institution: | (1) Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-7000 Stuttgart, Federal Republic of Germany;(2) Institut für Kristallographie der Universität Tübingen, Charlottenstrasse 33, D-7400 Tübingen, Federal Republik of Germany;(3) Present address: Department of Physics, Colorado State University, 80523 Fort Collins, CO, USA |
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Abstract: | The real part of the dielectric constant ![epsi](/content/n11n02u2gx43452x/xxlarge949.gif) , the heat capacityc
p, the infrared reflectivity, and the X-ray diffraction of TlGaSe2 have been measured in the temperature range from 12 K (30K) to 300 K. Both ![epsi](/content/n11n02u2gx43452x/xxlarge949.gif) andc
p show two anomalies at about 110 K and 120 K. A study of the hysteresis loop as well as an investigation of the dielectric dispersion in the microwave region show that the phase below 110 K is ferroelectric. The crystal structure remains nearly unchanged in the course of the phase transition. The loss of the
symmetry (C2/c Cc) results from small positional shifts of the T1 atoms in the ab plane accompanied by a discontinuity in the axial ratios. We suggest, that the ferroelectricity is caused by the stereochemically active electron lone pair configuration of the Tl+ ion. Thus TlGaSe2 may provide the first example for ferroelectricity caused by this mechanism. |
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