572 research outputs found
Structural phase transition and dielectric relaxation in Pb(Zn1/3Nb2/3)O3 single crystals
The structure and the dielectric properties of Pb(Zn1/3Nb2/3)O3 (PZN) crystal
have been investigated by means of high-resolution synchrotron x-ray
diffraction (with an x-ray energy of 32 keV) and dielectric spectroscopy (in
the frequency range of 100 Hz - 1 MHz). At high temperatures, the PZN crystal
exhibits a cubic symmetry and polar nanoregions inherent to relaxor
ferroelectrics are present, as evidenced by the single (222) Bragg peak and by
the noticeable tails at the basis of the peak. At low temperatures, in addition
to the well-known rhombohedral phase, another low-symmetry, probably
ferroelectric, phase is found. The two phases coexist in the form of mesoscopic
domains. The para- to ferroelectric phase transition is diffused and observed
between 325 and 390 K, where the concentration of the low-temperature phases
gradually increases and the cubic phase disappears upon cooling. However, no
dielectric anomalies can be detected in the temperature range of diffuse phase
transition. The temperature dependence of the dielectric constant show the
maximum at higher temperature (Tm = 417 - 429 K, depending on frequency) with
the typical relaxor dispersion at T < Tm and the frequency dependence of Tm
fitted to the Vogel-Fulcher relation. Application of an electric field upon
cooling from the cubic phase or poling the crystal in the ferroelectric phase
gives rise to a sharp anomaly of the dielectric constant at T 390 K and
diminishes greatly the dispersion at lower temperatures, but the dielectric
relaxation process around Tm remains qualitatively unchanged. The results are
discussed in the framework of the present models of relaxors and in comparison
with the prototypical relaxor ferroelectric Pb(Mg1/3Nb2/3)O3.Comment: PDF file, 13 pages, 6 figures collected on pp.12-1
Domain structure in the monoclinic Pm phase of Pb(Mg1/3Nb2/3)O3 - PbTiO3 single crystals
The domain structure of (1-x)Pb(Mg1/3Nb2/3)O3- xPbTiO3 single crystals with
composition x ~ 0.33 in the range of the morphotropic phase boundary (MPB) was
studied. Based on the analysis of spontaneous strain compatibility and charge
of domain walls, we have established the permissible domain arrangements for
the ferroelectric phases of different symmetry, which are expected to occur in
the range of the MPB. Examination of (001)-oriented unpoled and electrically
poled (along the [001] direction) crystal plates in polarizing microscope
reveals a monophase state with the domain structure compatible with the
structure theoretically predicted for the Mc monoclinic phase (space group Pm),
which was recently discovered in the compositions close to the MPB by x-ray and
neutron diffraction studies. In the unpoled crystal the 180 deg. walls between
the domains whose spontaneous polarization vectors are parallel to the plane of
the crystal plate (i.e. a-domains) are observed. The domain structure of the
poled crystal is predominantly composed of crystallographically prominent Wf
walls parallel to (001) (i.e. the plane of the crystal plate) and inclined S
walls parallel to [110] or [1-10] direction. In poled and unpoled samples the
optical rotatory polarization effect is found, which is related to the
inhomogeneity of the sample resulting from the mixture of domains.Comment: PDF file, 30 pages, 15 figures (3 in color) collected on pp.18-3
Possible impact of corporate governance profile on a Russian bank valuation
This paper aims at explaining the differences in valuation of banking firms in Russia through the impact of selected elements of corporate governance. We rely upon value-based management theory to test the hypothesis that expenses on corporate governance system create shareholder value. The price at which share stakes are acquired by strategic foreign investors is for us a criterion of market-proven value, so we use the standard valuation tool, i.e. price-to-book-value of equity (P/BV) multiple, as the dependent variable. The set of corporate governance parameters whose materiality for a would-be external investor we would like to test includes: the degree of concentration of ownership and control; maturity of corporate governing bodies; degree of Board independence; qualification of external auditors; stability of governing bodies (Management Board and Board of Directors); and availability of external credit ratings from the world's leading rating agencies. We test our approach on a sample of acquisition deals and public offerings over the period 2004-2008 that we develop for the first time. Firstly, we find out which factors are statistically significant and relevant to a bank's selling price. Secondly, a least squares multiple linear regression model is devised to check how each individual variable impacts the dependent variable. We discover that external investors attach value to high concentration of ownership, external credit rating coverage, stability of the Board of Directors, and involvement of well-established external auditors. Investors of a strategic nature tend to pay a higher acquisition premium. Independence of the Board of Directors might be perceived by external strategic investors as a disadvantage and might destroy shareholder value
Проектирование установки по переработке и утилизации нефтепродуктов
Современное развитие нефтяной отрасли предполагает наличие ресурсоэффективныхтехнологий, которые базируются на технических, экономических и экологических принципах.Нарушение технологических режимов транспортировки углеводородов может привести кневосполнимым потерям природных ресурсов и нанести существенный экологический ущерб. Поэтомумеждународные экологические стандарты ИСО 14000 предполагают повышенные видыответственности к предприятиям, допустившим указанные нарушения. Тем не менее, нефтяныекомпании ежегодно несут серьезные финансовые затраты, связанные с аварийными или чрезвычайнымиситуациями при транспорте нефти и нефтепродуктов. В связи с вышеуказанным, возникаетнеобходимость в совершенствовании существующих и разработке новых эффективных и быстрореализуемых технологий локализации и утилизации нефтяных разливов
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
Spin-glass state and long-range magnetic order in Pb(Fe1/2Nb1/2)O3
We have investigated the magnetic ground-state of the multiferroic relaxor
ferroelectric \pfn with SR spectroscopy and neutron scattering. We find
that a transition to a partially disordered phase occurs below T=20 K that
coexists with long-range antiferromagnetic ordering. The disordered phase
resembles a spin-glass. No clustering of magnetic ions could be evidenced by
SR so that the coexistence appears homogeneous in the sample
Direct Measurement of Piezoelectric Response around Ferroelectric Domain Walls in Crystals with Engineered Domain Configuration
We report the first investigation of the piezoelectric response on a
nanoscale in the poled ferroelectric crystals with engineered configuration of
domains. Piezoresponse force microscopy of tetragonal 0.63PMN-0.37PT
relaxor-based ferroelectric crystals reviled that the d33 piezoelectric
coefficient is significantly reduced within the distance of about 1 um from the
uncharged engineered domain wall. This finding is essential for understanding
the mechanisms of the giant piezoresponse in relaxor-based crystals and for
designing new piezoelectric materials
Monte Carlo Study of Relaxor Systems: A Minimum Model for Pb(InNb)O}
We examine a simple model for Pb(InNb)O (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
Direct observation of the formation of polar nanoregions in Pb(MgNb)O using neutron pair distribution function analysis
Using neutron pair distribution function (PDF) analysis over the temperature
range from 1000 K to 15 K, we demonstrate the existence of local polarization
and the formation of medium-range, polar nanoregions (PNRs) with local
rhombohedral order in a prototypical relaxor ferroelectric
Pb(MgNb)O. We estimate the volume fraction of the PNRs as a
function of temperature and show that this fraction steadily increases from 0 %
to a maximum of 30% as the temperature decreases from 650 K to 15 K.
Below T200 K the PNRs start to overlap as their volume fraction reaches
the percolation threshold. We propose that percolating PNRs and their
concomitant overlap play a significant role in the relaxor behavior of
Pb(MgNb)O.Comment: 4 pages, 3 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.
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