Crossover between ferroelectric order and dipolar glass disorder in betaine phosphate0.06betaine phosphite0.94mixed crystals

2015 ◽  
Vol 55 (2) ◽  
Author(s):  
Jūras Banys ◽  
Jan Macutkevic ◽  
Carola Klimm ◽  
Georg Völkel
Keyword(s):  
Phase Transition ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Landau Theory ◽  
Dielectric Strength ◽  
Freezing Temperature ◽  
Wide Frequency Range ◽  
Partial Ordering ◽  
Hydrogen Atoms ◽  
Temperature Dependences

The dielectric properties of mixed betaine phosphate0.06betaine phosphite0.94(BP0.06BPI0.94) ferroelectric crystals were investigated in a wide frequency range from 20 Hz to 3 GHz. Although the dielectric anomaly is clearly observed close to the ferroelectric phase transition temperatureTc= 121 K, the dielectric dispersion is very broad around and below this temperature. Temperature dependences of the dielectric strength, the mean relaxation frequency and the spontaneous polarization cannot be described together according to the Landau theory for ferroelectric phase transition with a single order parameter or according to the quasione-dimensional Ising model. The polarization shows a pronounced distribution in the ferroelectric phase and only a partial ordering of hydrogen atoms occurs down to the lowest temperatures. The unordered hydrogen atoms form a glassy phase and its formation is observed in dielectric spectra at very low temperatures. The proton freezing temperature was estimated.

A novel co-crystallization molecular ferroelectric induced by the ordering of sulphate anions and hydrogen atoms

2018 ◽  
Vol 5 (10) ◽  
pp. 2413-2419 ◽  
Author(s):  
Chang-Feng Wang ◽  
Ji-Xing Gao ◽  
Chao Li ◽  
Chang-Shan Yang ◽  
Jian-Bo Xiong ◽  
...  
Keyword(s):  
Phase Transition ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Dielectric Anomaly ◽  
Hydrogen Atoms

The co-crystallization complex [EG]·[Cu(phen)2·SO4] undergoes a paraelectric–ferroelectric phase transition around 272 K which was confirmed by the observation of a large dielectric anomaly.

Lattice-parameter measurements of PbHPO4 single crystals by the ratio method

1983 ◽  
Vol 16 (6) ◽  
pp. 623-628 ◽  
Author(s):  
J. Horváth
Keyword(s):  
Phase Transition ◽  
Single Crystals ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Lattice Parameter ◽  
Ratio Method ◽  
Monoclinic Crystal System ◽  
Monoclinic Crystal ◽  
Temperature Dependences ◽  
Crystal Lattice Parameters

Temperature dependences of PbHPO4 single-crystal lattice parameters were measured by the ratio method in the range 158–421 K. Below the ferroelectric phase transition (T c = 310 K) lattice parameter b increases non-linearly with decreasing temperature while all others decrease linearly. The ratio method was generalized to the monoclinic crystal system for this purpose.

scholarly journals Crossover from Ferroelectric to Relaxor Behavior in Ba1−xCaxTiO3 (x = 0.17) System

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2854
Author(s):  
Edita Palaimiene ◽  
Jan Macutkevic ◽  
Juras Banys ◽  
Antoni Winiarski ◽  
Irena Gruszka ◽  
...  
Keyword(s):  
Phase Transition ◽  
Dielectric Properties ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Relaxation Times ◽  
Wide Frequency Range ◽  
Relaxor Behavior ◽  
Arrhenius Law ◽  
Frequency Range ◽  
Ferroelectric Phase Transition Temperature

The dielectric properties of Ba1−xCaxTiO3 (x = 0.17) ceramics were studied in a wide frequency range of 20 Hz–53 GHz. Diffused ferroelectric phase transition was revealed close to 339 K in the dielectric properties of ceramics. The behaviour of distributions of relaxation times in vicinity of the ferroelectric phase transition temperature is also typical for order-disorder ferroelectric phase transition. However, at lower temperatures (below 200 K), the most probable relaxation increased according to the Arrhenius law. At lower temperatures the maximum of the imaginary part of dielectric permittivity versus temperature strongly shifted to higher temperatures when the frequency increased (from 125 K at 1.21 kHz to 300 K at 33 GHz). This behaviour was attributed to the dynamics of Ti ions. The origin of the crossover from ferroelectric to relaxor behaviour of Ba1−xCaxTiO3 (x = 0.17) ceramics is discussed in the paper.

scholarly journals The origin of the lattice thermal conductivity enhancement at the ferroelectric phase transition in GeTe

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Đorđe Dangić ◽  
Olle Hellman ◽  
Stephen Fahy ◽  
Ivana Savić
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Phase Transitions ◽  
Thermoelectric Materials ◽  
Ferroelectric Phase Transition ◽  
Lattice Thermal Conductivity ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
High Symmetry ◽  
Structural Phase Transitions

AbstractThe proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ. However, the κ of GeTe increases at the ferroelectric phase transition near 700 K. Using first-principles calculations with the temperature dependent effective potential method, we show that this rise in κ is the consequence of negative thermal expansion in the rhombohedral phase and increase in the phonon lifetimes in the high-symmetry phase. Strong anharmonicity near the phase transition induces non-Lorentzian shapes of the phonon power spectra. To account for these effects, we implement a method of calculating κ based on the Green-Kubo approach and find that the Boltzmann transport equation underestimates κ near the phase transition. Our findings elucidate the influence of structural phase transitions on κ and provide guidance for design of better thermoelectric materials.

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