Antiferroelectric phase transitions

Fig. 7 CP-MAS spectra of squaric acid, peak assignment and temperature variation in the close vicinity of its paraelectric-antiferroelectric phase transition [24], Note the pronounced coexistence of the spectra from the two phases...

Fig. 18 Temperature dependence of the CPMAS spectra of NH4H2ASO4 around the antiferroelectric phase transition temperature. The peaks corresponding to the paraelec-tric and antiferroelectric phases are labelled P and AF, respectively...

The temperature dependence of 1/Ti for is shown in Fig. 21. The discontinuity in the l/Ti data near Tn 216 K (highhghted by the arrow) appears at the onset of the antiferroelectric phase transition. Below Tn l/Ti increases abruptly from about 370 ms to 700 ms. 

Pociecha D, Gorecka E, Cepic M, Vaupotic N, Gomola K, Mieczkowski J (2005) Paraelectric-antiferroelectric phase transition in achiral liquid crystals. Phys Rev E 72 060701R... 

On the other hand, the proton potential of the 5-bromo compound is exactly symmetrical with reference to the reaction coordinate of the tautomerization. Consequently, the proton transfer can proceed through the tunnelling mechanism. This is the reason why the paraelectric behaviour is maintained even at 4 K. The suppression of the antiferroelectric phase transition may be derived from a quantum tunnelling effect. Such paraelectric behaviour can be regarded as quantum paraelectricity , which is a notion to designate the phenomenon that (anti)ferroelectric phase transitions are suppressed even at cryogenic temperatures due to some quantum-mechanical stabilization, proton tunnelling in this case. 

The dielectric response of PBSQ 2H2O derived from tautomerization is observed under atmospheric pressure and at ambient temperature. Furthermore, the dielectric constant turns out to be almost temperature-independent in the temperature range 4-300 K. When PBSQ was deuterated, the dielectric constant obeyed the Curie law, and an antiferroelectric phase transition was observed at 30 K. This result is strong supporting evidence for a significant contribution from the tunnelling mechanism to the dielectric response of the hydrogenous sample. 

Van Heurck C, Van Tendeloo G, Ghose S, Amehnckx S (1991) Paraelectric-antiferroelectric phase transition in titanite, CaTiSiOs. II. Electron diffraction and electron microscopic studies of transition dynamics. Phys Chem Miner 17 604-610... 

Sicron N, Yacoby Y, Stem EA, Dogan F (1997) XAFS study of the antiferroelectric phase transition in PbZr03. J Phys IV 7 1047-1049... 

T. Omura, C. Moriyoshi, K. Itoh, S. Ikeda, H. Fukazawa (2002). Ferroelectrics, 270, 1561-1566. Stmctural change of Cu(HC00)24H20 associated with the antiferroelectric phase transition. 

N.S. Dalai, K.L. Pierce, J. Palomar, R. Fu, Single-crystal magic-angle spinning O NMR and theoretical studies of the antiferroelectric phase transition in squaric acid,... 

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