Size and doping effects on the coercive field of ferroelectric nanoparticles

A microscopic model for describing ferroelectric nanoparticles is proposed which allows us to calculate the polarization as a function of an external electric field, the temperature, the defect concentration and the particle size. The interaction of the constituents of the material, arranged in layers, depends on both the coupling strength at the surface and that of defect shells in addition to the bulk values. The analysis is based on an Ising model in a transverse field, modified in such a manner to study the influence of size and doping effects on the hysteresis loop of the nanoparticles. Using a Green function technique in real space we find the coercive field, the remanent polarization and the critical temperature which differ significantly from the bulk behavior. Depending on the varying coupling strength due to the kind of doping ions and the surface configuration, the coercive field and the remanent polarization can either increase or decrease in comparison to the bulk behavior. The theoretical results are compared with a variety of different experimental data.Comment: 16 pages, 7 figure

Epitaxial growth and structural characterization of Pb(Fe1/2Nb1/2)O3 thin films

We have grown lead iron niobate thin films with composition Pb(Fe1/2Nb1/2)O3 (PFN) on (0 0 1) SrTiO3 substrates by pulsed laser deposition. The influence of the deposition conditions on the phase purity was studied. Due to similar thermodynamic stability spaces, a pyrochlore phase often coexists with the PFN perovskite phase. By optimizing the kinetic parameters, we succeeded in identifying a deposition window which resulted in epitaxial perovskite-phase PFN thin films with no identifiable trace of impurity phases appearing in the X-ray diffractograms. PFN films having thicknesses between 20 and 200 nm were smooth and epitaxially oriented with the substrate and as demonstrated by RHEED streaks which were aligned with the substrate axes. X-ray diffraction showed that the films were completely c-axis oriented and of excellent crystalline quality with low mosaicity (X-ray rocking curve FWHM<0.09). The surface roughness of thin films was also investigated by atomic force microscopy. The root-mean-square roughness varies between 0.9 nm for 50-nm-thick films to 16 nm for 100-nm-thick films. We also observe a correlation between grain size, surface roughness and film thickness.Comment: 13 Pages, 6 figures. To be published in J. Mag. Mag Mater. proceedings of EMRS200

A Proton Magnetic Resonance and Infrared Study of Colemanite and lnyoite

A proton magnetic resonance and IR investigation of colemanite, Ca B30 4 (0H) 3 • H 20 and inyoite, CaBa0a(OH) 5 • 4H20, is in agreement with the X-ray crystal structure analysist,2 concerning these two newly proposed formulae. It is confirmed that at room temperature there is a dynamic distribution of proton sites in the ferroelectric colem anite, while there is no such effect in inyoite. Ther~ are two second moment transitions in p. m. r. spectra of colemanite. The one at about -nooc is due to the onset of reorientation of water molecules. The second one at T c is discussed in terms of a dyna mic m odel involving a change from a symmetric double well potential for the moving protons into an asymmetric one below Tc

A Proton Magnetic Resonance and Infrared Study of Colemanite and lnyoite

A proton magnetic resonance and IR investigation of colemanite, Ca B30 4 (0H) 3 • H 20 and inyoite, CaBa0a(OH) 5 • 4H20, is in agreement with the X-ray crystal structure analysist,2 concerning these two newly proposed formulae. It is confirmed that at room temperature there is a dynamic distribution of proton sites in the ferroelectric colem anite, while there is no such effect in inyoite. Ther~ are two second moment transitions in p. m. r. spectra of colemanite. The one at about -nooc is due to the onset of reorientation of water molecules. The second one at T c is discussed in terms of a dyna mic m odel involving a change from a symmetric double well potential for the moving protons into an asymmetric one below Tc

Electron Paramagnetic Resonance in I-Irradiated Ferroelectric LiH3 (Seo;)2

Single crystals of LiH3(Se03) 2 were grown from water solution. The samples were exposed at room temperature to gamma radiation from a Co60 source and received doses of 106 r

Analytical calculation of the Peierls-Nabarro pinning barrier for one-dimensional parametric double-well models

Lattice effects on the kink families of two models for one-dimensional nonlinear Klein-Gordon systems with double-well on-site potentials are considered. The analytical expression of the generalized Peierls-Nabarro pinning potential is obtained and confronted with numerical simulations.Comment: RevTex, 10 pages, 4 figure

Superparaelectric phase in the ensemble of non-interacting ferroelectric nanoparticles

For the first time we predict the conditions of superparaelectric phase appearance in the ensemble of non-interacting spherical ferroelectric nanoparticles. The superparaelectricity in nanoparticle was defined by analogy with superparamagnetism, obtained earlier in small nanoparticles made of paramagnetic material. Calculations of correlation radius, energetic barriers of polarization reorientation and polarization response to external electric field, were performed within Landau-Ginzburg phenomenological approach for perovskites Pb(Zr,Ti)O3, BiFeO3 and uniaxial ferroelectrics rochelle salt and triglycine sulfate.Comment: 28 pages, 7 figures, 3 Appendices, to be submitted to Phys. Rev.