Comparative analysis of methods for studying internal stresses in crystals

The possibilities provided by the main polarization optical methods of studying internal stresses in differently oriented plates prepared from cubic crystals are compared. A promising method for obtaining exhaustive information on the stressed state of an object, including the trajectories and the values of the principal stresses, is described.     

Interlayer for matching crystal lattices in the domain walls of ferroelastic lead orthophosphate

The possible existence of an interlayer with the symmetry of the paraphase in the W and W′ domain walls of lead orthophosphate has been checked from the condition of matching the crystal lattices of adjacent domains. It is shown that two types of interlayers are possible, which possess different symmetries, strain tensors, matrices of the rotation of the coordinate system, thicknesses, and elastic energies. It is shown that the domain-wall energy is proportional to the squared spontaneous deformation.     

Balanced and unbalanced domain walls in Pb3(PO4)2

The equations of domain walls in the vicinity of a phase transition are obtained from the condition of the deformation balance at phase boundaries and domain walls for a ferroelastic lead orthophosphate crystal. All domain walls can be divided into three groups, in accordance with the conditions of their formation-balanced, conventionally balanced, and unbalanced domain walls. The structure of staggered domain walls is suggested.     

Ferroelastic domain walls in BiVO<Subscript>4</Subscript>

Analysis of the domain structure is performed using the method of matching strains at the interface and the model of thin domain walls. Equations describing the matching interlayers for crystal lattices are derived and the interlayer parameters are obtained for all possible types of domain walls in BiVO₄. It is shown that the matching interlayers have monoclinic symmetry. A difference between the elastic energy of a domain wall and the parameters of adjacent orientation states is revealed.     

Dynamic magnetic charges of domain walls and their influence on microwire magnetoimpedance

Domain walls in Co-based amorphous microwires with high-frequency current are investigated by the magnetoimpedance measurements. Dynamic stray fields of magnetic charges on domain walls were found out. In frame of the Landau–Lifshits approach the influence of the magnetic charges interactions on the microwire magnetoimpedance is studied. Parameter describing lowering of the magnetoimpedance is obtained.     

An improved time domain analysis of the charge pumping current

A new time domain analysis of the charge pumping phenomenon in metal-oxide-semiconductor field-effect transistors is presented. With this theoretical approach we model the traps filling and the charge pumping current with any gate signal waveform and any energy distribution of the interface traps in the semiconductor bandgap. A method is also presented for the determination of the energy levels reached at the end of the non-steady-state emission of electrons and holes. The theoretical charge pumping response of a single trap is also investigated for uniform and non-uniform substrate doping profiles.     

On the reproducibility of the orientation distribution function of texture samples from pole figures (IV). Reproduction methods

The known reproduction methods for determination of the orientation distribution function from pole figures are discussed from the view of the structure of their solutions of the problem. The exact solution of the reproduction problem is derived.     

Diffraction methods analysis of the approximation of the real glass structure

X-ray and electron diffraction methods are discussed and the results of an analysis of glass structure are reported.Experimental methods were employed to analyse the structures of a series of complex oxide glasses of the type:

$\text{SiO}{}_2\text{(～72\%)+}\text{Na}{}_2\text{O}\text{(～14\%)+}\text{CaO}\text{(～8\%) +}\text{MgO}\text{(～4\%)+R}{}_2\text{O}{}_3\text{(～2\%)}$

.In calculating the structural parameters of the real glass structure the assumed effective molecule was approximated which included from two (SiO₂) to five (SiO₂Na₂OCaOMgO) groups of various atoms. The structural parameters obtained allowed the real internal structure to be established and were employed in the construction of a space model of the glass.The most probable structural models are presented, obtained by successive approximation with individual oxide groups added one after another. The models' structural and physicochemical parameters were chosen to be consistent with those of the nodal model which is near to the real glass structure. The parameters required to construct the nodal model in question were established by analysing radial distribution functions and by the differentiation of the adequate radial distribution functions by subtraction and successively approximating the effective molecule including the oxide groups (SiO₂, Na₂O, CaO and MgO) added one after another.An aperiodic model of a nodal lattice is presented in a scheme, stressing the structural parameters and local orderings in groups describing the internal structure of complex oxide glasses. Also, an approximate nodal space model of great importance for the construction of a structural model of glass is presented and discussed with regard to its utility and accuracy in the determination of its parameters.     

Application of the Fourier transforms for analysis of the domain structure images of uniaxial ferroelectric

The formation of ferroelectric domains in triglycine sulfate crystal in the para–ferroelectric phase transition has been investigated in situ by piezoresponse force microscopy. The domain structure has been analyzed using the images of Fourier transforms of the scanned (010) surface of natural cleavage. The formation of a quasi-periodic one-dimensional structure of 180° domains with dominant components of one sign below T _C near the transition point is revealed and crystallographic reference to the laboratory coordinate system is performed.     

Crystal structure analysis of two terpene derivatives

The crystal structures of two terpene derivatives, 2,4,5,6,7,7a-hexahydro-7a-hydroxy-3,6-dimethyl-2-benzofuranone (compound I) and β-cyclolavandulic acid (compound II), were determined by single-crystal diffractometry. Compound I, C₁₀H₁₄O₃, crystallizes in the orthorhombic space group P2₁2₁2₁ with the unit cell parameters a = 6.715(1) Å, b = 7.043(1) Å, c = 20.292(3) Å, and Z = 4. The six-membered ring has an ideal chair conformation. The five-membered ring is planar. Compound II, C₁₀H₁₆O₂, crystallizes in the monoclinic space group P2₁/n with the unit cell parameters a = 8.446(1) Å, b = 12.156(1) Å, c = 9.901(1) Å, β = 106.29(1)°, and Z = 4. The cyclohexene ring exhibits a half-chair conformation. Both the crystal structures are stabilized by intermolecular O-H?O hydrogen bonds.     

Comparative crystal chemical analysis of borophosphates and borosilicates

A comparative crystal chemical analysis of mixed borophosphate and borosilicate anionic radicals revealed the main difference between them: the condensation of [PO₄] tetrahedra does not proceed via common vertices, whereas the sharing of vertices is possible for the [SiO₄] tetrahedra. In all the borophosphates considered, phosphorus is found only in the formally isolated tetrahedra. The central part of the heterogeneous radicals is formed by tetrahedra of lower charge ions (B⁺³), and the tetrahedra that incrust the central part have higher valences (Si⁺⁴, P⁺⁵). In borosilicates, silicon forms its own constructions up to complex layers and frameworks because its charge (Si⁺⁴) is lower than that of phosphorus (P⁺⁵). The higher charge of phosphorus impedes two-dimensional and three-dimensional condensation. As a result, borophosphates form a variety of soro and chain radicals and only few layer and framework constructions.     

Statistic analysis of partition coefficients for crystallization cleaning methods

Statistic estimation of experimental determination reliability for the distribution coefficient, K, (crystal-melt equilibrium) has been made on the basis of independent measurement comparison. Reliability of these data is shown to be low. Frequency K histograms have been constructed both for simple element set and halogenides. Histogram maximum shift to lg K < 0 has been obtained.     

Complex zigzag flexoelectric walls in the Schlieren textures of MBBA: possibility for determination of two basic Schlieren textures with singular or non‐singular surface points

The flexo‐dielectric behaviour of a homeotropic MBBA nematic layer has been experimentally studied. Asymmetric strong‐weak anchoring of the homeotropic nematic layer was achieved by treating the glass plates – one of them with lecithin ensuring the strong anchoring and the other with usual soap ensuring the weak anchoring. The application of a dc voltage with a sufficient amplitude led to the appearance of a complex texture consisting of gradient flexo‐dielectric deformations including Schlieren texture with many singular points and zigzag flexoelectric walls. The application of additional orienting a.c. voltage brought clarification of the Schlieren texture resembling that of the smectic‐C liquid crystal. Inversely, the application of an ac voltage across the homeotropic nematic layer led to formation of a nice Schlieren texture. The additional application of a d.c. voltage created complex zigzag gradient flexoelectric walls which connected the singular points in the Schlieren texture. In this way, one can determine for the first time how many points in the initial Schlieren texture are singular and how many points are non‐singular. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparative analysis of the structural and morphological features of biogenic and synthesized goethite nanoparticles

Crystallography Reports - A comparative analysis of the relationship between the morphological forms and magnetic properties of natural goethite particles from the crust of weathering of the Far...     

A new method for the investigation of orientation relationships in meteoritic plessite

The orientation relationship (OR) between the bcc and fcc phase in the plessite microstructure of the iron meteorites Watson, Agpalilik and Gibeon has been analysed in a scanning electron microscope using electron back‐scattered diffraction (EBSD). A very strong OR exists, independently on the analysed plessite type and the observed spreading of single orientation data. The agreement between the experimental orientation distribution and existing models varies for each meteorite. The black plessite in the Agpalilik corresponds to the Nishiyama‐Wassermann model whereas the duplex plessite of the Gibeon meteorite shows an OR close to the Kurdjumov‐Sachs model. The Watson meteorite is strongly deformed so that a general OR is difficult to determine due to the blurred experimental orientation distribution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new method for the determination of the orientation of molecules in the unit cell

A new method for the determination of the orientation of organic molecules with partially known stereochemistry in the unit cell is described and compared with the convolution molecule method by Hoppe and Paulus.     

Magnetic susceptibility calculation of semiconductor compounds AIIIBV in the MOLCAO approximation

A semiempirical model for calculating magnetic susceptibility, which allows to substantiate the magnetic susceptibility dependence on the crystal symmetry and the nature of interatomic interaction in it, has been proposed. Diamagnetic term of magnetic susceptibility in one electron approximation together with radius mean square of atoms in the A^IIIB^V compound is shown to be determined by the distance, position of gravity center of charge cloud, the degree of covalency of the compound and the overlapping integrals. Paramagnetic term of magnetic susceptibility in the approximation of the first coordination sphere is determined by the averaged transition energy between the excited and unexcited p-levels of the system, the bond nature in a semiconductor and the overlapping integrals. Numerical results satisfactorily agree with the experimental data.     

On the orientation dependence of effective distribution coefficients of impurities

Germanium crystals doped by antimony are grown by the Czochralski technique along 12 different crystallographic directions. The effective distribution coefficients (K_ef) are determined here. It is shown that orientation dependence of k_ef could be explained by supercooling at growth surfaces correlating with number of layer systems {111} crossing that surfaces and with angles between that systems and direction of shift of the crystallization front.