scholarly journals Calculation of the Spontaneous Polarization and the Dielectric Constant as a Function of Temperature for

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
Hamit Yurtseven ◽  
Sema Şen
Keyword(s):  
Dielectric Constant ◽  
Transition Temperature ◽  
Temperature Dependence ◽  
Spontaneous Polarization ◽  
Atmospheric Pressure ◽  
Ferroelectric Phase ◽  
Paraelectric Phase ◽  
Soft Mode ◽  
Increasing Temperature ◽  
Mode Response

The temperature dependence of the spontaneous polarizationPis calculated in the ferroelectric phase of KH2PO4(KDP) at atmospheric pressure (TC= 122 K). Also, the dielectric constantεis calculated at various temperatures in the paraelectric phase of KDP at atmospheric pressure. For this calculation ofPandε, by fitting the observed Raman frequencies of the soft mode, the microscopic parameters of the pure tunnelling model are obtained. In this model, the proton-lattice interaction is not considered and the collective proton mode is identified with the soft-mode response of the system. Our calculations show that the spontaneous polarization decreases continuously in the ferroelectric phase as approaching the transition temperatureTC. Also, the dielectric constant decreases with increasing temperature and it diverges in the vicinity of the transition temperature (TC= 122 K) for KDP according to the Curie-Weiss law.

Theory of Ferroelectric Phase Transitions in Pure and Mixed Perovskites.

2002 ◽  
Vol 718 ◽  
Author(s):  
Yizhak Yacoby ◽  
Yakov Girshberg
Keyword(s):  
Temperature Dependence ◽  
Ferroelectric Phase ◽  
Paraelectric Phase ◽  
Soft Mode ◽  
Critical Concentration ◽  
Comprehensive Model ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Ferroelectric Phase Transitions ◽  
Basic Experimental Data

AbstractWe present a comprehensive model of ferroelectricity in oxygen perovskite crystals that account quantitatively for both displacive like and order-disorder like properties. The model assumes that in the paraelectric phase, the system has a soft mode, interacting with spontaneous disordered off-center displacements. The resulting theory is shown to quantitatively explain the properties of two representative perovskites: KNbO3 and PbTiO3. We have further extended this theory to explain the properties of mixed incipient ferroelectrics with small concentrations of ferroelectricity inducing ions such as KTa1-xNbxO3. The model quantitatively reproduces the basic experimental data in the quantum regime: the temperature dependence of the inverse dielectric function, the impurity and temperature dependence of the renormalized soft mode vibrational frequency and the impurity concentration dependence of the transition temperature Tc. In particular we show that, the critical concentration for Tc=0 is determined by the ion tunneling frequency, the bare soft mode parameters and the pseudospin - phonon coupling constant.

Change of Phase Transition Temperature in Band Engineered Ferroelectric Lanthanum-Modified Bismuth Titanates

2020 ◽  
Vol 20 (11) ◽  
pp. 7135-7139
Author(s):  
Rui Tang ◽  
Sangmo Kim ◽  
Chung Wung Bark
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Transition Temperature ◽  
Phase Transition Temperature ◽  
Ferroelectric Properties ◽  
Solar Spectrum ◽  
Ferroelectric Material ◽  
Transition Temperatures ◽  
Phase Transition Temperatures ◽  
Increasing Temperature

The ferroelectric material chosen for a solar cell has to absorb as much of the solar spectrum as possible, therefore a low band gap is desirable, but it is rarely known for phase transition temperature on the bandgap engineered ferroelectric materials. The phase transition temperature of a ferroelectric material can be determined by monitoring its dielectric constant with increasing temperature, as the dielectric constant changes abruptly at the phase transition temperature. Here, we inform the measurement of the phase transition temperature of the ferroelectric complex oxide Bi3.25La0.75Ti3O12 as well as cobalt and iron doped Bi3.25La0.75Ti3O12 bulk ceramics for photovoltaic cells based on dielectric monitoring with changing temperature. We synthesized lanthanum-modified bismuth-titanate-based ceramics with various doping concentrations transition metal to Ti. X-ray diffraction analysis revealed that all the compounds crystallized in an orthorhombic structure. Their morphologies and size distributions were observed using scanning electron microscopy. From the ultraviolet-visible spectroscopy absorption spectra of the synthesized powder, bandgaps were checked. An inductance-capacitance-resistance meter was used to obtain the relationship between dielectric responses and the temperature of the targets in a tube furnace. We observed that the dielectric constant increases gradually with increasing temperature, until the transition temperature and subsequently decreases, and we were able to determine the phase transition temperatures of the tested materials. Furthermore, the results revealed that all the doped bismuth titanates keep their phase transition temperatures, which were sufficiently high, to maintain their ferroelectric properties above room temperature.

Impedance and Dielectric Properties of Nb-Doped Pb(Zr0.52Ti0.48)O3 Ceramics

2008 ◽  
Vol 55-57 ◽  
pp. 129-132
Author(s):  
Piyachon Ketsuwan ◽  
Athipong Ngamjarurojana ◽  
Yongyut Laosiritaworn ◽  
Supon Ananta ◽  
Rattikorn Yimnirun ◽  
...  
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Paraelectric Phase ◽  
Dopant Concentration ◽  
Rhombohedral Phase ◽  
Paraelectric Phase Transition ◽  
Nb Content ◽  
Dielectric Maximum ◽  
Increasing Temperature ◽  
Curie Temperature Tc

The compositions of Pb(Zr0.52Ti0.48)O3 doped with 1-6 mole% Nb content were prepared by a conventional mixed oxide technique. It was found that the phase formed depended on the dopant concentration. At lower concentration, the dominate phase was the tetragonal. With increasing Nb content the rhombohedral phase tended to increase. Furthermore, the Curie temperature (Tc) and dielectric constant decreased with increasing Nb concentration and the dielectric maximum peaks were broadened with more rhombohedral phase presence, causing the diffused ferroelectric-paraelectric phase transition. The impedance of the samples decreased with increasing temperature and it was also observed that the impedance increased with increasing Nb concentration.

STUDIES ON ORIENTED DOMAIN POLYSTYRENE-TGS COMPOSITE FILMS

1995 ◽  
Vol 09 (17) ◽  
pp. 1039-1044
Author(s):  
S.C. MATHUR ◽  
D.S. RAWAT ◽  
H.O. YADAV ◽  
D.C. DUBE ◽  
A.S. BHALLA
Keyword(s):  
Dielectric Constant ◽  
Transition Temperature ◽  
Dielectric Properties ◽  
Domain Structure ◽  
Spontaneous Polarization ◽  
Coercive Field ◽  
Composite Films ◽  
Microwave Frequency ◽  
Ferroelectric Films ◽  
Microwave Frequencies

Polymer ferroelectric films were prepared by dispersing TGS powder in polystyrene. Permittivity versus temperature plots exhibit a peak at around the transition temperature of TGS. The peak gets suppressed with increasing frequency and the trend continues up to microwave frequencies. We observed that the dielectric constant of films at microwave frequency stays close to the dielectric constant of polystyrene. The domain structure of TGS crystals essentially seems to affect their dielectric properties. Single domain films exhibit a higher spontaneous polarization and a higher coercive field.

Temperature Dependence of Soft Mode Frequency and Dielectric Constant in Ferroelectric PbHPO[sub 4] Crystal

2011 ◽  
Author(s):  
Trilok Chandra Upadhayay ◽  
Mayank Joshi ◽  
P. K. Bajpai ◽  
K. S. Ojha ◽  
K. N. Singh
Keyword(s):  
Dielectric Constant ◽  
Temperature Dependence ◽  
Soft Mode ◽  
Mode Frequency

The Microstructure and Dielectric Properties of SrTiO3 Modified 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Ceramics

2011 ◽  
Vol 687 ◽  
pp. 433-438
Author(s):  
Jing Song Liu ◽  
Tao Li ◽  
Hui Qin Li ◽  
You Chao Xu ◽  
Ji Qiang Yu
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Transition Temperature ◽  
Dielectric Properties ◽  
Spontaneous Polarization ◽  
Relaxor Behavior ◽  
Maximum Dielectric Constant ◽  
Lower Temperature ◽  
Region Size ◽  
Maximum Permittivity

The microstructure and dielectric properties of ferroelectric solutions which is formulated with (1-x)[0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3]-x mol% SrTiO3(x=0, 1, 3 and 5) have been investigated. The ceramics was fabricated by a modified columbite route sintered at 1200 °C. The effects of dopants on microstructure, maximum dielectric constant (εm) and diffuseness of the phase transition, etc. have been studied. It is found that the maximum permittivity (εm) increases to 24968 for the ST-doped (1 mol %) sample, subsequently decreases with ST addition and its corresponding phase-transition-temperature (Tm) shifts to the lower temperature. The variation of εmis caused by the decrease of polar nano-region size, increase of the fluctuation of the component and the increase of the effective spontaneous polarization. The enhancement of relaxor behavior in the PMN-PT sample is explained by the decrease of FE/AFE coupling.

Study of Inelastic Light Scattering in LaxSr(1-1.5x)TiO3

2008 ◽  
Vol 587-588 ◽  
pp. 148-152
Author(s):  
A. Almeida ◽  
Tatiana M. Correia ◽  
M.R. Chaves ◽  
Paula M. Vilarinho ◽  
Andréi L. Kholkin
Keyword(s):  
Transition Temperature ◽  
Low Temperatures ◽  
Lattice Dynamics ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
Soft Mode ◽  
Grain Structure ◽  
Inelastic Light Scattering ◽  
Raman Study ◽  
A Site

In an attempt to gain a better understanding of the lattice dynamics in lanthanum doped SrTiO3 (STO) ceramics, with general formulae LaxSr(1-1.5x)TiO3, we have carried out a detailed Raman study of the x=0.0133 ceramic in the temperatures ranging from 10K to room temperature. Our results show that lanthanum substitution gives rise to new features in the Raman spectra. The Rayleigh band and the extra Raman-forbidden infrared active modes observed provide evidence for the existence of disorder in the system, apparently associated with grain structure, and lattice defects. Moreover, the absence of a TO1 polar soft mode supports the non-existence of a ferroelectric phase at low temperatures. The shift of the para-antiferrodistorsive transition temperature towards higher temperatures clearly evidences that the replacement of Strontium by Lanthanum occurs at the lattice A-site.

Temperature Dependence of Barkhausen Noise Parameters in Carbon Steel

2007 ◽  
Vol 537-538 ◽  
pp. 371-380
Author(s):  
L. Harasztosi ◽  
Lajos Daróczi ◽  
I.A. Szabó ◽  
Z. Balogh ◽  
Dezső L. Beke
Keyword(s):  
Transition Temperature ◽  
Temperature Dependence ◽  
Probability Distributions ◽  
Barkhausen Noise ◽  
Inflexion Point ◽  
Exciting Field ◽  
Brittle Transition ◽  
Ductile Brittle Transition Temperature ◽  
Brittle Transition Temperature ◽  
Increasing Temperature

Temperature dependence of different parameters (the position of the inflexion point and the saturation value on the root main square, RMS, values versus exciting field curves) of the Barkhausen noise is measured in structural steel (S 235 JRG1). It is shown that while the position of the inflexion point remained constant, the RMS value at the inflexion point and saturation value increased with the increasing temperature, T. Most interestingly the field required for saturation decreased with decreasing temperature and had a breakpoint at about 200K. Breakpoints at the same temperature on the critical exponents versus temperature functions (i.e. on the β(T) and α(T) curves, where β and α are the exponents of the probability distributions of peak heights and durations, respectively) were also observed. This temperature can be identified as the ductile-brittle transition temperature.

Correlation Between the Anomalous Pressure Dependence of the Superconducting Transition Temperature in Thallium and the Temperature Dependence of its Knight Shift

1974 ◽  
Vol 52 (8) ◽  
pp. 678-686 ◽  
Author(s):  
J. Schratter ◽  
D. Llewelyn Williams
Keyword(s):  
Transition Temperature ◽  
Temperature Dependence ◽  
Pressure Dependence ◽  
Superconducting Transition Temperature ◽  
Knight Shift ◽  
Superconducting Transition ◽  
Electronic Density ◽  
Nonlinear Variation ◽  
Volume Dependence ◽  
Increasing Temperature

A study of the Knight shift has been carried out on a single crystal of thallium. The isotropic Knight shift decreases with increasing temperature, showing a nonlinear variation which is most pronounced between 50 and 150 K. This behavior is correlated with the anomalous pressure dependence of the superconducting transition temperature at low pressure. From the superconducting data on pure Tl and Tl–Hg alloys, we extract the volume dependence of the electronic density of states, and use it to derive the temperature dependence of the Knight shift. The results agree with the observed data.

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