Change from 3D-Ising to random field-Ising-model criticality in a uniaxial relaxor ferroelectric.
Pyroelectric measurements of polarization have been used to determine the temperature dependence of the polarization in strontium barium niobate, SBN:Ce, close to its phase transition temperature T(c) approximately 317 K. A gradual increase of the critical exponent from beta approximately 0.13 to beta approximately 0.30 is observed when decreasing the initial polarization from 100% to 0.8% of the saturation value. A change from three-dimensional random-field Ising to pure Ising model behavior is conjectured and explained by a gradual compensation of quenched random electric fields by those emerging from charged fractal nanodomain walls.
Institut für Mineralogie, Universität zu Köln, Zülpicherstrasse 49b, D-50674 Cologne, Germany.
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Granzow
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Woike
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Wöhlecke
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Imlau
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Kleemann