Surface and Size Effects in TGS, NaNO2, and DKDP Nanocrystals

2000 ◽  
Vol 655 ◽  
Author(s):  
Juan D. Romero ◽  
Luis F. Fonseca ◽  
Rafael Ramos ◽  
Manuel I. Marqués ◽  
Julio A. Gonzalo
Keyword(s):  
Phase Transition ◽  
Monte Carlo ◽  
Ising Model ◽  
Monte Carlo Simulations ◽  
Size Effects ◽  
Paraelectric Phase ◽  
Paraelectric Phase Transition ◽  
Model Hamiltonian ◽  
Phase Transition Temperatures ◽  
Polarization Temperature

AbstractMonte Carlo simulations of some typical order-disorder ferroelectrics such as TGS, NaNO2 and DKDP nanocrystals were studied using a Transverse Ising Model Hamiltonian with four-spins interactions. The microscopic parameters corresponding to this Hamiltonian were adjusted to fit the experimental polarization-temperature curves for each one of the materials in the bulk phase. Then the dependences of the ferroelectric-paraelectric phase transition temperatures, Tc, on the sizes of those crystals were studied with Monte Carlo simulations of the order-disorder system. We report a weak dependence of Tc on the size of the crystal (d) for these materials above d∼6nm. The addition of surface effects showed that the expected lowtemperature shift of Tc due to size effects, can be reverted.

Surface and size effects on the Ferroelectric Phase Transition and Surface Polarization of Thin Films: Monte Carlo Simulations

1997 ◽  
Vol 493 ◽  
Author(s):  
J. Romero ◽  
L. F. Fonseca
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Ferroelectric Phase Transition ◽  
Ferroelectric Phase ◽  
First Order ◽  
Surface Polarization ◽  
Ferroelectric Phase Transition Temperature ◽  
Model Hamiltonian

ABSTRACTThe macroscopic polarization of ferroelectric thin films was studied by Monte Carlo simulations using a Transverse Ising Model Hamiltonian with four-spins interactions. The dependence of the ferroelectric phase transition temperature, Tc, on the thickness of the film was obtained resulting in a shifting of Tc towards lower temperatures and a change from first-order to second-order phase transition as the thickness of the film is reduced. Comparison between the surface and internal order was carried out by the calculation of layer-averaged polarizations as a function of the sample temperature and the surface interaction parameters. These comparisons show that increasing disorder at the surface can be reverted by increasing the four-spins surface interactions.

scholarly journals Wide Electrocaloric Temperature Range Induced by Ferroelectric to Antiferroelectric Phase Transition

2019 ◽  
Vol 9 (8) ◽  
pp. 1672 ◽  
Author(s):  
Xiaohui Sun ◽  
Houbing Huang ◽  
Hasnain Mehdi Jafri ◽  
Junsheng Wang ◽  
Yongqiang Wen ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Efficiency ◽  
Paraelectric Phase ◽  
Operating Temperature ◽  
Paraelectric Phase Transition ◽  
Temperature Range ◽  
Antiferroelectric Phase ◽  
Phase Transition Temperatures ◽  
Cooling Devices ◽  
Operating Temperature Range

The ferroelectric (FE) to antiferroelectric (AFE) phase transition tuning the temperature range of electrocaloric (EC) effects was investigated using phenomenological Landau–Devonshire theory. Contrary to ferroelectric to paraelectric (PE) phase transitions for electrocaloric effects, the ferroelectric to antiferroelectric phase transition was adopted to obtain large entropy changes under an applied electric field in a Sm-doping BiFeO3 system. In addition, the doping composition and hydrostatic pressure was observed to tune the ferroelectricantiferroelectric–paraelectric phase transition temperatures and broaden the operating temperature range of electrocaloric effects. The optimal wide temperature range of ~78 K was observed at 3 GPa compressive hydrostatic pressures and 0.05 Sm-doping BiFeO3. The present study paves the way to designing high efficiency cooling devices with larger operating temperature spans.

scholarly journals MAJORITY-VOTE MODEL ON (3, 4, 6, 4) AND (34, 6) ARCHIMEDEAN LATTICES

2006 ◽  
Vol 17 (09) ◽  
pp. 1273-1283 ◽  
Author(s):  
F. W. S. LIMA ◽  
K. MALARZ
Keyword(s):  
Phase Transition ◽  
Monte Carlo ◽  
Ising Model ◽  
Monte Carlo Simulations ◽  
Critical Exponents ◽  
Majority Vote ◽  
Embedding Dimension ◽  
Vote Model ◽  
Disorder Phase Transition ◽  
Regular Lattices

On Archimedean lattices, the Ising model exhibits spontaneous ordering. Two examples of these lattices of the majority-vote model with noise are considered and studied through extensive Monte Carlo simulations. The order/disorder phase transition is observed in this system. The calculated values of the critical noise parameter are qc = 0.091(2) and qc = 0.134(3) for (3, 4, 6, 4) and (34, 6) Archimedean lattices, respectively. The critical exponents β/ν, γ/ν and 1/ν for this model are 0.103 (6), 1.596 (54), 0.872 (85) for (3, 4, 6, 4) and 0.114 (3), 1.632 (35), 0.98 (10) for (34, 6) Archimedean lattices. These results differs from the usual Ising model results and the majority-vote model on so-far studied regular lattices or complex networks. The effective dimensionalities of the system [D eff (3, 4, 6, 4) = 1.802(55) and D eff (34, 6) = 1.860(34)] for these networks are reasonably close to the embedding dimension two.

scholarly journals MAJORITY-VOTE ON DIRECTED BARABÁSI–ALBERT NETWORKS

2006 ◽  
Vol 17 (09) ◽  
pp. 1257-1265 ◽  
Author(s):  
F. W. S. LIMA
Keyword(s):  
Phase Transition ◽  
Monte Carlo ◽  
Ising Model ◽  
Monte Carlo Simulations ◽  
Decay Time ◽  
Order Parameter ◽  
Majority Vote ◽  
Arrhenius Law ◽  
Vote Model ◽  
Disorder Phase Transition

On directed Barabási–Albert networks with two and seven neighbours selected by each added site, the Ising model was seen not to show a spontaneous magnetisation. Instead, the decay time for flipping of the magnetisation followed an Arrhenius law for Metropolis and Glauber algorithms, but for Wolff cluster flipping the magnetisation decayed exponentially with time. On these networks the Majority-vote model with noise is now studied through Monte Carlo simulations. However, in this model, the order-disorder phase transition of the order parameter is well defined in this system. We calculate the value of the critical noise parameter qc for several values of connectivity z of the directed Barabási–Albert network. The critical exponentes β/ν, γ/ν and 1/ν were calculated for several values of z.

AVRAMI–KOLMOGOROV–JOHNSON–MEHL KINETICS FOR NANOPARTICLES

2008 ◽  
Vol 15 (05) ◽  
pp. 605-612 ◽  
Author(s):  
VLADIMIR P. ZHDANOV
Keyword(s):  
Phase Transition ◽  
Activation Energy ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Infinite Medium ◽  
Local State ◽  
Elementary Reaction ◽  
Regular Surface

In the conventional Avrami–Kolmogorov–Johnson–Mehl model, the reaction or phase transition occurring in the 2D or 3D infinite medium is considered to start and proceed around randomly distributed and/or appearing nucleation centers. The radius of the regions transformed is assumed to linearly increase with time. The Monte Carlo simulations presented, illustrate what may happen if the transformation takes place in nanoparticles. The attention is focused on nucleation on the regular surface, edge and corner sites, and on the dependence of the activation energy for elementary reaction events on the local state of the sites.

Sign in / Sign up

Export Citation Format

Share Document