Phase diagram for K(1-x)(NH4)(x)H2PO4 (x = 0 – 0.15) solid solutions embedded into magnetic glasses

Effect of magnetic field application on phase transition in nanostructured solid solutions (1-x)KH2PO4 – (x)(NH4)H2PO4 at x = 0, 0.05 and 0.15 has been studied by dielectric spectroscopy at B = 0 – 10T. The samples have been prepared by impregnation of magnetic porous glasses by KDP-ADP solid solutions. The average pore diameter in glasses was 50(5) nm. The temperatures of the ferroelectric phase transition have been determined, and the phase diagrams for these nanocomposite materials (NCM) on cooling and heating (including at magnetic field application) were constructed. The interface “matrix-nanoparticles” was shown to play the principal role in phase diagram formation

Dynamical effects of the nanometer-sized polarized domains in Pb(Zn1/3Nb2/3)O3

Recent neutron scattering measurements performed on the relaxor ferroelectric Pb[(Zn1/3Nb2/3)0.92Ti0.08]O3 (PZN-8%PT) in its cubic phase at 500 K, have revealed an anomalous ridge of inelastic scattering centered ~0.2 A-1 from the zone center (Gehring et al., Phys. Rev. Lett. 84, 5216 (2000)). This ridge of scattering resembles a waterfall when plotted as a phonon dispersion diagram, and extends vertically from the transverse acoustic (TA) branch near 4 meV to the transverse optic (TO) branch near 9 meV. No zone center optic mode was found. We report new results from an extensive neutron scattering study of pure PZN that exhibits the same waterfall feature. We are able to model the dynamics of the waterfall using a simple coupled-mode model that assumes a strongly q-dependent optic mode linewidth Gamma1(q) that increases sharply near 0.2 A-1 as one approaches the zone center. This model was motivated by the results of Burns and Dacol in 1983, who observed the formation of a randomly-oriented local polarization in PZN at temperatures far above its ferroelectric phase transition temperature. The dramatic increase in Gamma1 is believed to occur when the wavelength of the optic mode becomes comparable to the size of the small polarized micro-regions (PMR) associated with this randomly-oriented local polarization, with the consequence that longer wavelength optic modes cannot propagate and become overdamped. Below Tc=410 K, the intensity of the waterfall diminishes. At lowest temperatures ~30 K the waterfall is absent, and we observe the recovery of a zone center transverse optic mode near 10.5 meV.Comment: 8 pages, 9 figures (one color). Submitted to Physical Review

Disorder and relaxation mode in the lattice dynamics of PbMg1/3_{1/3}Nb2/3_{2/3}O3_3 relaxor ferroelectric

The low-energy part of vibration spectrum in PbMg$_{1/3}$Nb$_{2/3}$O$_3$ relaxor ferroelectric was studied by inelastic neutron scattering. We observed the coexistence of a resolution-limited central peak with strong quasielastic scattering. The line-width of the quasielastic component follows a $\Gamma_0+Dq^2$ dependence. We find that $\Gamma_0$ is temperature-dependent. The relaxation time follows the Arrhenius law well. The presence of a relaxation mode associated with quasi-elastic scattering in PMN indicates that order-disorder behaviour plays an important r\^ole in the dynamics of diffuse phase transitions

Effects Associated with Confined Geometry in Nanocomposites Based on Mesoporous 2D SBA 15 and 3D SBA 15 Matrices Containing Sodium Nitrite Nanoparticles

Temperature dependences of the ferroelectric order parameter for nanostructured sodium nitrite under heating and cooling were obtained by analyzing the temperature evolution of diffraction spectra of neutron scattering by composites obtained by introducing sodium nitrite into pores of mesoporous 2D SBA 15 the average pore diameter is 69 4 and 3D SBA 15 94 5 matrices. It was demonstrated that the phase transition to the paraelectric phase in the process of heating occurs at TC 433 1 K in both nanocomposite materials. It was found that these sizes decrease at approaching to the ferroelectric phase transition point on heating. Temperature hysteresis 15 20 K in the temperature dependence of the order parameter between the heating and cooling regimes was reveale