Etude quantitative de l'énergie libre de PbZrO3 pur et dopé avec Nb2O5

1969 ◽  
Vol 47 (22) ◽  
pp. 2439-2443 ◽  
Author(s):  
L. Benguigui ◽  
H. Hervet
Keyword(s):  
Free Energy ◽  
Ferroelectric Phase ◽  
Paraelectric Phase ◽  
Temperature Phase ◽  
Phase Determination ◽  
Electrical Field ◽  
Antiferroelectric Phase ◽  
Field Temperature ◽  
Heat Transition

Pure and Nb2O5 doped PbZrO3 exhibit the following phases: antiferroelectric, ferroelectric, and paraelectric. By means of measurements of heat transition, dielectric constant in paraelectric phase, determination of electrical field – temperature phase diagrams, we calculate the free energy of each phase. Given that the free energy can be developed in powers of the polarization, we show the coefficients of the ferroelectric phase are slightly modified by the addition of Nb2O5, while those of the antiferroelectric phase vary by a factor greater than two.

Neutron structures of ammonium tetrafluoroberyllate

1999 ◽  
Vol 55 (1) ◽  
pp. 17-23 ◽  
Author(s):  
R. C. Srivastava ◽  
W. T. Klooster ◽  
T. F. Koetzle
Keyword(s):  
Hydrogen Bonding ◽  
Ferroelectric Phase ◽  
Paraelectric Phase ◽  
Accurate Determination ◽  
Mirror Plane ◽  
Accurate Information ◽  
X Ray ◽  
The Past ◽  
Hydrogen Bonding Interactions

It is thought that hydrogen bonding is responsible for the ferroelectricity in ammonium tetrafluoroberyllate, (NH_{4})_{2}BeF_{4}. In the past X-ray data have been collected, but these did not permit accurate determination of the H-atom positions. In order to obtain more accurate information the neutron structures have now been determined for the paraelectric and ferroelectric phases. Going from the paraelectric to the ferroelectric phase, both the BeF_4^{2-} and the NH_4^+ ions rotate and shift from the mirror planes of the paraelectric phase. This results in removal of the mirror-plane symmetry and formation of a superlattice with the a axis doubled. Along the polar c axis, the NH_4^+ ions move towards the BeF_4^{2-} ions within chains of molecules and the chains move slightly relative to one another. The rotations and translations give rise to stronger hydrogen-bonding interactions.

scholarly journals Crystal structures of di-tin-hexa(seleno)hypodiphosphate, Sn2P2Se6, in the ferroelectric and paraelectric phase

1998 ◽  
Vol 213 (1) ◽  
Author(s):  
R. Israël ◽  
R. de Gelder ◽  
J. M. M. Smits ◽  
P. T. Beurskens ◽  
S. W. H. Eijt ◽  
...  
Keyword(s):  
Molecular Structure ◽  
High Temperature ◽  
Low Temperature ◽  
Ferroelectric Phase ◽  
Paraelectric Phase ◽  
Crystal And Molecular Structure ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Monoclinic System ◽  
Low Temperature Phase

AbstractThe crystal and molecular structure of SnIn both phases, the structure crystallizes in the monoclinic system. The ferroelectric phase withComparison of the two structures showed that the tin ions shift to positions of about 0.13 Å from an individual disorder-site in the high temperature phase (paraelectric) to the corresponding tin position in the low temperature phase (ferroelectric). The shift from the average Sn-position in the paraelectric phase to the Sn-positions in the ferroelectric phase is about 0.30 Å (on average 10° off the vector

Dielectric Study of the Ferroelectric Phase Transition in DMAGaS Crystal

1998 ◽  
Vol 53 (3-4) ◽  
pp. 105-111 ◽  
Author(s):  
R. Tchukvinskyi ◽  
R. Cach ◽  
Z. Czapla
Keyword(s):  
Phase Transition ◽  
Electric Field ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
Paraelectric Phase ◽  
Dielectric Study ◽  
Electric Permittivity ◽  
First Order ◽  
Dc Electric Field

Abstract Electric permittivity measurments as functions of temperature at constant dc electric field and as functions of the dc electric field at constant temperatures in the paraelectric phase have been performed for DMAGaS crystal. The changes of the permittivity maximum with the electric field intensity evidence the first-order character of the ferroelectric phase transition at Tc1. The field dependence of the permittivity ε(E) in the paraelectric phase is discussed, using the classical electric equation of state. A method for the determination of the corresponding coefficients is proposed. The obtained B and C coefficients, together with double hysteresis loop observed above Tc1 prove the first-order character of the ferroelectric phase transition in DMAGaS crystal.

Direct phase determination in electron crystallography: small organic molecules

1992 ◽  
Vol 50 (2) ◽  
pp. 1166-1167
Author(s):  
Douglas L. Dorset
Keyword(s):  
Organic Molecules ◽  
Data Sets ◽  
Temperature Structure ◽  
3D Analysis ◽  
Intensity Data ◽  
Electron Crystallography ◽  
Phase Determination ◽  
Measured Intensity ◽  
3D Data

The quantitative use of electron diffraction intensity data for the determination of crystal structures represents the pioneering achievement in the electron crystallography of organic molecules, an effort largely begun by B. K. Vainshtein and his co-workers. However, despite numerous representative structure analyses yielding results consistent with X-ray determination, this entire effort was viewed with considerable mistrust by many crystallographers. This was no doubt due to the rather high crystallographic R-factors reported for some structures and, more importantly, the failure to convince many skeptics that the measured intensity data were adequate for ab initio structure determinations.We have recently demonstrated the utility of these data sets for structure analyses by direct phase determination based on the probabilistic estimate of three- and four-phase structure invariant sums. Examples include the structure of diketopiperazine using Vainshtein's 3D data, a similar 3D analysis of the room temperature structure of thiourea, and a zonal determination of the urea structure, the latter also based on data collected by the Moscow group.

scholarly journals Field-temperature phase diagram of the enigmatic Nd2(Zr1−xTix)2O7 pyrochlore magnets

2021 ◽  
Vol 103 (21) ◽  
Author(s):  
M. Léger ◽  
E. Lhotel ◽  
E. Ressouche ◽  
K. Beauvois ◽  
F. Damay ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Temperature Phase ◽  
Field Temperature ◽  
Temperature Phase Diagram

scholarly journals On factors affecting surface free energy of carbon black for reinforcing rubber

2020 ◽  
Vol 9 (1) ◽  
pp. 170-181 ◽  
Author(s):  
Shangyong Zhang ◽  
Ruipeng Zhong ◽  
Ruoyu Hong ◽  
David Hui
Keyword(s):  
Free Energy ◽  
Carbon Black ◽  
Surface Free Energy ◽  
Surface Activity ◽  
Gas Flow ◽  
Influential Factors ◽  
Chromatographic Column ◽  
Factors Affecting ◽  
Carrier Gas Flow

AbstractThe surface activity of carbon black (CB) is an important factor affecting the reinforcement of rubber. The quantitative determination of the surface activity (surface free energy) of CB is of great significance. A simplified formula is obtained to determine the free energy of CB surface through theoretical analysis and mathematical derivation. The surface free energy for four kinds of industrial CBs were measured by inverse gas chromatography, and the influential factors were studied. The results showed that the aging time of the chromatographic column plays an important role in accurate measurement of the surface free energy of CB, in comparison with the influences from the inlet pressure and carrier gas flow rate of the chromatographic column filled with CB. Several kinds of industrial CB were treated at high temperature, and the surface free energy of CB had a significant increase. With the increase of surface free energy, the maximum torque was decreased significantly, the elongation at break tended to increase, the heat generation of vulcanizates was increased, and the wear resistance was decreased.

Chemical sensing failed by aggregation-caused quenching? A case study enables liquid/solid two-phase determination of N2H4

2021 ◽  
Vol 415 ◽  
pp. 128975
Author(s):  
Xiangqian Li ◽  
Mengqing Li ◽  
Yuze Chen ◽  
Gongxi Qiao ◽  
Qian Liu ◽  
...  
Keyword(s):  
Chemical Sensing ◽  
Phase Determination ◽  
Two Phase
Sign in / Sign up

Export Citation Format

Share Document