Micro Mechanism of BaTiO3 Ferroelectric Phase Transition Described by Electron Cloud Model

2012 ◽  
Vol 479-481 ◽  
pp. 619-622
Author(s):  
Chao Fang ◽  
Liang Yan Chen
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Equilibrium Position ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Cloud Model ◽  
Electron Cloud ◽  
Oxygen Ions ◽  
Expansion Effect ◽  
Coulomb Attraction

In this paper the micro mechanism of BaTiO3 ferroelectric phase transition is studied based on the thermodynamic model using electron cloud model, and further the Curie - Weiss law is explained. The results indicate that the contraction of the electron cloud, as the temperature decreased through Curie temperature, causes oxygen ions shift the equilibrium position, and the Coulomb attraction makes Ti ion shift the equilibrium position causing phase transition; With temperature rising, the ion displacement polarization decreases owing to the electron cloud expansion effect, and the variation of dielectric constant with temperature follows the Curie - Weiss law.

Para-Ferroelectric Phase Transition Induces Excellent Second Harmonic Generation Response and Prominent Switchable Dielectric Constant Change based on a Metal-Free Ionic Crystal

CrystEngComm ◽  
2021 ◽  
Author(s):  
Ding-Chong Han ◽  
Yu-Kong Li ◽  
Yao Liu ◽  
Yu-Hui Tan ◽  
Yun Zhi Tang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Ionic Crystal ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Second Harmonic ◽  
Metal Free ◽  
Reversible Phase Transition ◽  
Constant Change ◽  
Reversible Phase

In this paper, a novel metal-free compound: [H2(bpyp)][ClO4]2 (1), (bpyp = 1,3-bis(4-pyridyl) propane), has been successfully synthesized, its undergoing a reversible phase transition around Tc = 256.19 K (Tc is...

Dielectric characteristics and diffuse ferroelectric phase transition in Sr4La2Ti4Nb6O30 tungsten bronze ceramics

2006 ◽  
Vol 21 (7) ◽  
pp. 1787-1792 ◽  
Author(s):  
X.L. Zhu ◽  
X.M. Chen ◽  
X.Q. Liu ◽  
Y. Yuan
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Tungsten Bronze ◽  
Frequency Dispersion ◽  
Dielectric Characteristics ◽  
Low Dielectric ◽  
Dielectric Data ◽  
Maximum Dielectric Constant

In this work, Sr4La2Ti4Nb6O30 ceramics with tetragonal filled tungsten bronze structure were prepared, and the dielectric characteristics and ferroelectric transition were investigated. The room-temperature dielectric constant of the present ceramics showed very weak frequency dependency; it decreased from 570.4 to 561.7 when the frequency varied from 200 Hz to 1 MHz, and a comparatively low-dielectric loss was observed (in the order of 10−3). Unlike the situation for Ba4Ln2Ti4Nb6O30 (Ln = La, Nd and Sm), Sr4La2Ti4Nb6O30 ceramics showed a diffuse ferroelectric phase transition, and the diffuseness exponent γ was 1.61. Moreover, the obvious frequency dispersion was observed over a broad frequency range from 200 Hz to 1 MHz, and the maximum dielectric constant temperature Tmax shifted to higher temperatures with increasing frequency. The dielectric data agreed closely with the Vogel–Fulcher relationship. We concluded that tungsten bronze Sr4La2Ti4Nb6O30 has the relaxor ferroelectric nature.

Research of the Mechanism of Ferroelectric Phase Transition in Perovskite: Empty Orbital Model

2011 ◽  
Vol 130-134 ◽  
pp. 2809-2812
Author(s):  
Chao Fang ◽  
Liang Yan Chen
Keyword(s):  
Phase Transition ◽  
Curie Temperature ◽  
Temperature Dependence ◽  
Bond Energy ◽  
Equilibrium Position ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Point Of View ◽  
Repulsion Energy ◽  
The Impact

The empty orbital model in perovskite ATiO3-type (A=Mg, Ca, Sr and Ba) ferroelectrics with oxygen octahedra has been proposed. In this study, the impact of temperature on the bond energy of Ti-O has been discussed from the point of view of statistical thermodynamics, then the temperature dependence of equilibrium position of Ti ion has been calculated. The results show that because of the existence of empty orbital, with temperatrue decreasing the repulsion energy of Ti and O ions reduces and the Ti ion shift the equilibrium position in the cooling through the Curie temperature owing to Coulomb interaction. Ferroelectric phase transition in perovskite are successfully explained. Theoretical and experimental results for perovskite ATiO3-type ferroelectrics are compared and discussed.

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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