scholarly journals Broadband and infrared spectroscopy of Ag0.98Li0.02NbO3 ceramics

2020 ◽  
Vol 60 (4) ◽  
Author(s):  
Edita Palaimienė ◽  
Jan Macutkevič ◽  
Jūras Banys ◽  
Irena Gruszka ◽  
Antoni Kania
Keyword(s):  
Phase Transition ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
Microwave Frequency ◽  
Frequency Range ◽  
Temperature Dependent ◽  
Low Frequencies ◽  
Microwave Dielectric ◽  
Ferroelectric Phase Transition Temperature ◽  
Ferroelectric Domains

The dielectric properties of Ag0.98Li0.02NbO3 (ALN2) ceramics were investigated in a broad frequency range (20 Hz – 60 THz). The dielectric spectra of ALN2 ceramics are mainly impacted by electrical conductivity at higher temperatures (above 400 K) and low frequencies (below 100 Hz), ferroelectric domains below ferroelectric phase transition temperature Tc = 330 K and at low frequencies (below 1 MHz), and contribution of the soft ferroelectric mode, the frequency of which is below 50 cm–1. All phononic modes are slightly temperature dependent, thus confirming the influence of Ag, O and Li ions dynamics on the phase transitions. However, the most important contribution to the dynamics of phase transition is made by Nb ions. Ceramics exhibits a huge value of dielectric permittivity and relatively low losses in a microwave frequency range (ε΄ ≈ 250 and ε˝ ≈ 20 at 10 GHz and room temperature), indicating that it is suitable for various microwave dielectric applications.

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 Local ferroelectric polarization switching driven by nanoscale distortions in thermoelectric $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Aastha Vasdev ◽  
Moinak Dutta ◽  
Shivam Mishra ◽  
Veerpal Kaur ◽  
Harleen Kaur ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Figure Of Merit ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Direct Evidence ◽  
Temperature Dependent ◽  
Force Microscopy ◽  
Ferroelectric Domains ◽  
Pdf Analysis ◽  
Ferroelectric Transition Temperature

AbstractA remarkable decrease in the lattice thermal conductivity and enhancement of thermoelectric figure of merit were recently observed in rock-salt cubic SnTe, when doped with germanium (Ge). Primarily, based on theoretical analysis, the decrease in lattice thermal conductivity was attributed to local ferroelectric fluctuations induced softening of the optical phonons which may strongly scatter the heat carrying acoustic phonons. Although the previous structural analysis indicated that the local ferroelectric transition temperature would be near room temperature in $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$ Sn 0.7 Ge 0.3 Te , a direct evidence of local ferroelectricity remained elusive. Here we report a direct evidence of local nanoscale ferroelectric domains and their switching in $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$ Sn 0.7 Ge 0.3 Te using piezoeresponse force microscopy(PFM) and switching spectroscopy over a range of temperatures near the room temperature. From temperature dependent (250–300 K) synchrotron X-ray pair distribution function (PDF) analysis, we show the presence of local off-centering distortion of Ge along the rhombohedral direction in global cubic $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$ Sn 0.7 Ge 0.3 Te . The length scale of the $${\text {Ge}}^{2+}$$ Ge 2 + off-centering is 0.25–0.10 Å near the room temperatures (250–300 K). This local emphatic behaviour of cation is the cause for the observed local ferroelectric instability, thereby low lattice thermal conductivity in $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$ Sn 0.7 Ge 0.3 Te .

Relation between tolerance factor and Tc in Aurivillius compounds

2001 ◽  
Vol 16 (11) ◽  
pp. 3139-3149 ◽  
Author(s):  
Donají Y. Suárez ◽  
Ian M. Reaney ◽  
William E. Lee
Keyword(s):  
Room Temperature ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
Tolerance Factor ◽  
Structural Phase Transitions ◽  
Aurivillius Phases ◽  
Ferroelectric Phase Transition Temperature ◽  
Transmission Electron ◽  
Octahedral Tilting ◽  
Permittivity Measurements

The structures and microstructures of a range of Aurivillius phases were investigated by transmission electron microscopy. Systematic rows of superlattice reflections arising from tilting of octahedra around the c axis were identified, and their intensities at room temperature were shown to diminish as the tolerance factor (t) of the perovskite blocks increased. For compounds with t's approaching 1, no superlattice reflections were observed. the paraelectric-to-ferroelectric phase transition temperature (Tc) was monitored through permittivity measurements as a function of temperature, and Tc was also shown to decrease as t increased. Consequently, the onset of octahedral tilting and Tc appeared to be strongly related Aurivillius phases. Planar defects arising from the structural phase transitions and from stacking irregularities were also discussed.

Ferroelectricity of trimethylammonium bromide below room temperature

2020 ◽  
Vol 8 (17) ◽  
pp. 5868-5872 ◽  
Author(s):  
Zhangran Gao ◽  
Yuying Wu ◽  
Zheng Tang ◽  
Xiaofan Sun ◽  
Zixin Yang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Curie Temperature ◽  
Ferroelectric Phase Transition ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
First Order

Ferroelectricity of trimethylammonium bromide was discovered near room temperature, which undergoes a first-order paraelectric–ferroelectric phase transition at the Curie temperature around 286 K.

Origin of ferroelectric phase transition in SbSClxI1-x mixed crystals

2014 ◽  
Vol 28 (30) ◽  
pp. 1450209 ◽  
Author(s):  
A. Audzijonis ◽  
L. Žigas ◽  
R. Sereika ◽  
R. Žaltauskas
Keyword(s):  
Phase Transition ◽  
Free Energy ◽  
Temperature Dependence ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Harmonic Approximation ◽  
Temperature Dependent ◽  
Normal Coordinate ◽  
Unit Cell Parameters ◽  
Cell Parameters

The measurements of SbSCl x I 1-x(x = 0.2) temperature dependent capacitance were carried out. The temperature of ferroelectric phase transition TC ≈340 K was measured experimentally. TC of SbSCl x I 1-x was calculated theoretically in anharmonic and harmonic approximations. TC was calculated in anharmonic approximation using temperature dependence of mean potential energy of Sb atoms as a function of the soft B1u symmetry normal coordinate along c(z)-axis. Moreover, TC was calculated in harmonic approximation using temperature dependence of vibrational thermodynamic functions (Helmholc free energy). TC dependence from unit cell parameters a, b and from mixture composition x was carried out.

Observation of unusual temperature-dependent stripes in LiTaO3and LiTaxNb1−xO3crystals with near-zero birefringence

2010 ◽  
Vol 43 (6) ◽  
pp. 1305-1313 ◽  
Author(s):  
A. M. Glazer ◽  
Nan Zhang ◽  
Ausrine Bartasyte ◽  
D. S. Keeble ◽  
S. Huband ◽  
...  
Keyword(s):  
Phase Transition ◽  
Room Temperature ◽  
Paraelectric Phase ◽  
Microscopy Study ◽  
Vapour Transport ◽  
Temperature Dependent ◽  
Paraelectric Phase Transition ◽  
Optical Birefringence ◽  
Self Organized ◽  
Li Content

A birefringence imaging microscopy study of LiTaO3and some mixed LiTaxNb1−xO3crystals is reported. The initially congruent LiTaO3crystals have been subject to vapour transport equilibration in order to increase the Li content and at the same time to reduce the optical birefringence close to zero at room temperature. In both types of crystal, the presence of unusual periodic self-organized stripes, existing over large distances, has been observed, which correlate with the well documented cleavage and twin planes in this material. Furthermore, the stripes become narrower as the temperature is changed away from the zero-birefringence temperature, but become temperature-independent above the ferroelectric–paraelectric phase-transition temperature.

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