Decoupling of the order-disorder and displacive contributions to the phase transition in NH4H(ClH2CCOO)2 |
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Authors: | Maria Zdanowska-Fr?czek Piotr Czarnecki |
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Affiliation: | a Institute of Molecular Physics, Polish Academy of Sciences, 60-179 Poznań, Smoluchowskiego 17, Poland b Faculty of Chemistry, Wroc?aw University, 50-385 Wroc?aw, Joliot-Curie 14, Poland c Faculty of Physics of Adam Mickiewicz University, Umultowska 85, 60-614 Poznań, Poland |
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Abstract: | The effects of hydrostatic pressure and substitution of Rb+for the ammonium cations on the ferroelectric phase transition temperature in NH4H(ClH2CCOO)2 have been studied by electric permittivity measurements. The transition temperature (Tc) decreases with increasing pressure up to 800 MPa and the pressure coefficient dTc/dp=−1.4×10−2 [K/MPa] has been experimentally determined. The substitution of Rb+ for the ammonium cations has been shown to considerably lower the ferroelectric phase transition temperature Tc. In mixed crystals, additional electric permittivity anomaly has been clearly evidenced. The results are discussed assuming a model, which combines polarizability effects, related to the heavy ion units, with the pseudo-spin tunnelling. |
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Keywords: | C. High pressure D. Ferroelectricity D. Phase transitions |
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