Development of Ferroelectric Order in Relaxor (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3

The microstructure and phase transition in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) and its solid solution with PbTiO3 (PT), PMN-xPT, remain to be one of the most puzzling issues of solid state science. In the present work we have investigated the evolution of the phase symmetry in PMN-xPT ceramics as a function of temperature (20 K < T < 500 K) and composition (0 <= x <= 0.15) by means of high-resolution synchrotron x-ray diffraction. Structural analysis based on the experimental data reveals that the substitution of Ti^4+ for the complex B-site (Mg1/3Nb2/3)^4+ ions results in the development of a clean rhombohedral phase at a PT-concentration as low as 5%. The results provide some new insight into the development of the ferroelectric order in PMN-PT, which has been discussed in light of the kinetics of polar nanoregions and the physical models of the relaxor ferroelectrics to illustrate the structural evolution from a relaxor to a ferroelectric state.Comment: Revised version with updated references; 9 pages, 4 figures embedde

Monte Carlo Study of Relaxor Systems: A Minimum Model for Pb(In1/2_{1/2}Nb1/2_{1/2})O3_3}

We examine a simple model for Pb(In$_{1/2}$Nb$_{1/2}$)O$_3$ (PIN), which includes both long-range dipole-dipole interaction and random local anisotropy. A improved algorithm optimized for long-range interaction has been applied for efficient large-scale Monte Carlo simulation. We demonstrate that the phase diagram of PIN is qualitatively reproduced by this minimum model. Some properties characteristic of relaxors such as nano-scale domain formation, slow dynamics and dispersive dielectric responses are also examined.Comment: 5 pages, 4 figure

Effect of high pressure on multiferroic BiFeO3

We report experimental evidence for pressure instabilities in the model multiferroic BiFeO3 and namely reveal two structural phase transitions around 3 GPa and 10 GPa by using diffraction and far-infrared spectroscopy at a synchrotron source. The intermediate phase from 3 to 9 GPa crystallizes in a monoclinic space group, with octahedra tilts and small cation displacements. When the pressure is further increased the cation displacements (and thus the polar character) of BiFeO3 is suppressed above 10 GPa. The above 10 GPa observed non-polar orthorhombic Pnma structure is in agreement with recent theoretical ab-initio prediction, while the intermediate monoclinic phase was not predicted theoretically.Comment: new version, accepted for publication in Phys. Rev.

A muon-spin relaxation study of BiMnO3

We present the results of muon-spin relaxation measurements on ferromagnetic BiMnO3. Below T_C=98.0(1) K oscillations in the time-dependence of the muon polarization are observed, characteristic of a quasistatic magnetic field at a single muon site, allowing us to probe the critical behaviour associated with the magnetic phase transition. We are able to suggest candidate muon sites on the basis of dipole field calculations. Close to T_C, fluctuations of the Mn^3+ moments are characteristic of critical behaviour while there is a sharp crossover to a region of fast dynamic fluctuations at higher temperatures.Comment: 10 pages, 4 figure

Novel patented minimally invasive technique for surgical treatment of varicocele: technique overview

Introduction. Many methods have been proposed for the surgical treatment of varicocele, the most of which is of historical significance. At present, there is no consensus in favor of one or another method of surgical treatment of varicocele, which determines the relevance of further research.Objective. To evaluate the effectiveness of a new minimally invasive method of surgical treatment of varicocele using the author's method.Materials &amp; methods. The study enrolled 763 patients aged 18 – 46 years (mean age 26.3 years) with varicocele who underwent testicular vein subinguinal ligation according to the author's technique. Inclusion criteria: varicocele grades 1 – 3, aged ≥ 18 years, semen abnormalities according to semen analysis and dilated spermatic cord veins according to ultrasound, retrograde blood flow according to Doppler ultrasound. Exclusion criteria: previously operated patients with recurrent varicocele, patients with May-Thurner syndrome and bilateral varicocele. The examination included eight control points: before surgery and 3, 6, 12, 24, 36, 48, and 60 months after surgery. Physical scrotal examination with Valsalva test, semen analysis, and Dopper scrotal ultrasound were performed at the control dates.Results. The average surgery time was 15 min (10 – 30 min). All patients were discharged 1 to 2 days after surgery. At follow-up for 60 months, patients showed improvement in spermatogenesis / or no progression of semen abnormalities during follow-up after surgery based on clinical, laboratory and instrumental studies (semen analysis, ultrasound / Doppler ultrasound); no data on testicular hypotrophy, hydrocele were revealed. A scrotal haematoma was detected in one patient in the early postoperative period. Recurrent varicocele (1.4%) was detected in 11 patients during the follow-up period.Conclusion. The technique is effective, easily reproducible, characterised by a low rate of recurrence and postoperative complications

Phonon and magnon scattering of antiferromagnetic Bi2Fe4O9

The phonon structure of antiferromagnetic Bi2Fe4O9 (space group Pbnm No. 55, TN≈240  K) was studied theoretically by calculations of lattice dynamics and experimentally between 10 and 300 K by polarized Raman spectroscopy. Most of the 12Ag+12B1g+9B2g+9B3g Raman modes were unambiguously identified. Strong second-order scattering was observed for ab-plane-confined incident and scattered light polarizations. In addition to the phonon-scattering, broad Raman bands with typical characteristics of magnon scattering appear below TN. The magnon bands are analyzed on the basis of magnetic structure of Bi2Fe4O9 and attributed to two- magnon excitations

Experimental evidence for an intermediate phase in the multiferroic YMnO3

We have studied YMnO$_{3}$ by high-temperature synchrotron X-ray powder diffraction, and have carried out differential thermal analysis and dilatometry on a single crystal sample. These experiments show two phase transitions at about 1100K and 1350K, respectively. This demonstrates the existence of an intermediate phase between the room temperature ferroelectric and the high temperature centrosymmetric phase. This study identifies for the first time the different high-temperature phase transitions in YMnO$_{3}$.Comment: 10 pages 5 figures. New version, Additional data, Journal of Physics: Condensed Matter, in Pres

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

Soft Phonon Anomalies in the Relaxor Ferroelectric Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3

Neutron inelastic scattering measurements of the polar TO phonon mode dispersion in the cubic relaxor Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3 at 500K reveal anomalous behavior in which the optic branch appears to drop precipitously into the acoustic branch at a finite value of the momentum transfer q=0.2 inverse Angstroms, measured from the zone center. We speculate this behavior is the result of nanometer-sized polar regions in the crystal.Comment: 4 pages, 4 figure