Formation of a quasi-equilibrium domain structure of crystals of the TGS group near TC

In the temperature range ΔT ≈ 321 K ÷ 322 K, the kinetics of the nonequilibrium domain structure of triglycine sulphate crystals, both pure and with specially introduced defects, has been studied by means of piezoresponse force microscopy technique. The temporal change in the domain structure as a set of regions with a scalar order parameter of P (r, t) = +1 and −1 for oppositely polarized domains was analysed by the behaviour of the space-time correlation function C(r,t) = ·Р(r,t)Р(0,t)Ò. At different distances from the Curie point Tc, the characteristic length Lc, as a scale measure of the average domain size, increases with time according to the power law Lc(t)~(t−t0)a. A decrease of the exponent a with distance from Tc can be a consequence of the transition of the domain structure of TGS crystals from a non-conservative state to aconservative one.

Improvement of Wrinkles in Roll-to-Roll Microwave Plasma CVD Graphene

ABSTRACTWrinkle-less graphene films are obtained through roll-to-roll microwave plasma chemical vapor deposition by using flexible copper/polyimide (Cu/PI) webs. Raman spectra suggests that the average domain size of the obtained graphene on the flexible Cu/PI is almost the same compared to the graphene on a Cu web that includes wrinkles. Also, by utilizing the flexible Cu/PI webs, the compressive strains decreased. The sheet resistances of graphene deposited on the Cu/PI are (1∼5)×104Ω, which is two orders of magnitude lower than those of graphene deposited on the Cu webs. Our results suggest that the controlling the expansion of web material an important technology to improve graphene transparent conductive properties.

Domain structure investigation of non-stoichiometric strontium ferrites and cobaltites

Monte Carlo domain structure simulation and Debye equation calculation of XRD patterns were used to confirm the formation of domain structure and investigate its peculiarities. Correspondence of simulated XRD patterns with synchrotron powder diffraction experiments is achieved on the conditions that beside of 90o rotations of brownmillerite-like domains inside perovskite-like matrix each domain contains areas with perpendicularly oriented tetrahedral chains. Influence of such parameters as stoichiometry, average domain size, orthorhombic distortion degree on the XRD patterns is considered.

Raman Spectroscopy and XPS Analysis of Epitaxial Graphene Grown on 4H-SiC (0001) Substrate under an Argon Pressure of 900 mbar Environment

This paper investigated a feasible process of growing epitaxial graphene on 4H hexagonal poly-type of silicon carbide Si-faced polar surface (0001) under an argon pressure of 900 mbar conditions. Using Raman Spectroscopy, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, epitaxial graphene grown at temperature 1600°C is confirmed to take shape weakly on 4H-SiC (0001) with an average domain size of several tens of nanometers, and this can be seen as the characteristic of initial formation of epitaxial graphene on substrate.

Structural Properties of 3C-SiC Grown by Sublimation Epitaxy

The present paper deals with morphological and structural investigation of 3C-SiC layers grown by sublimation epitaxy on on axis 6H-SiC(0001) at source temperature 2000 °C, under vacuum conditions (<10-5 mbar) and different temperature gradients in the range of 5-8 °C/mm. The layer grown at a temperature gradient 6 °C/mm has the largest average domain size of 0.4 mm2 assessed by optical microscope in transmission mode. The rocking curve full width at half maximum (FWHM) of (111) reflection is 43 arcsec which suggests good crystalline quality. The AFM image of the same layer shows steps with height 0.25 nm and 0.75 nm which are characteristic of a stacking fault free 3C-SiC surface and c-axis repeat height, respectively.

Ordered Structures in Ba(Cd1/3Ta2/3)O3 Microwave Ceramics: A Transmission Electron Microscopy Study

ABSTRACTOrdered structures of Ba(Cd1/3Ta2/3)O3 ceramics with and without boron additive were investigated systemically by electron diffraction and high resolution transmission electron microscopy. The results showed a well-ordered structure of 1:2 with hexagonal symmetry for Ba(Cd1/3Ta2/3)O3 with boron additive. No significant changes in ordered structures were observed after long-period annealing. The 1:2 ordered domain structures (average domain size ∼18 nm) and high-density domain boundaries induced by ordering were observed for Ba(Cd1/3Ta2/3)O3 without boron additive sintered at relatively high temperature. The sintering process has a profound influence on the microstructure of Ba(Cd1/3Ta2/3)O3 ceramics.

Selective Interactions in Elastomers, a Base for Compatibility and Polymer-Filler Interactions

This paper describes the determination of accurate solubility parameters for nonpolar rubbers according to a GLC-method developed by Guillet. The data obtained provide a simple but meaningful thermodynamic characterization of the contribution of microstructure units and comonomers (styrene) in polydienes. On this basis quantitative expressions are derived for δ2-parameters of BR and SBR as a function of the vinyl and the styrene content respectively. The consequences on morphology development and miscibility are presented for blends of NR, SBR, BR and EPDM. Furthermore, it is shown for the first time that the method is able to describe the temperature dependence of the δ2-parameter so that temperature induced phase transitions (UCST and LCST) can be predicted. On this basis morphological predictions are made on average domain size and size distribution as well as on the phase inversion region. The contribution of intermolecular interactions to flow-induced phase morphology is discussed in relation to the influence of rheological factors. An extension to polymer—filler systems is made.

Synchrotron X-Ray Diffraction Study of the Surface Layer in Poled Ceramic BaTiO3#

Both unpoled and poled BaTiO3 were studied by laboratory and synchrotron x-ray sources. The shorter-wavelength synchrotron radiation was used to probe deeper below the specimen surface. Diffraction patterns revealed a distinctive surface layer of the same tetragonal structure as the main BaTiO3 fraction. A sin2 Ψ analysis of peak shift confirmed that no measurable change of elastic strain occurs upon poling. This indicates that poling may induce excessive strain that was relieved by microcracking or that a majority of domains reverse orientation. However, domain switching and possible microcracking may induce inhomogeneous strain (microstrain) and alter domain-size distribution. Line-broadening analysis showed large anisotropy of both coherently diffracting domain size and microstrain. The poled specimen shows a larger microstrain and smaller average domain size, which indicates possible effects of microcracking and additional defects created during poling.