Magnetic properties of the CrSxTe1−x (x = 0−0.2) solid solutions

On the basis of X-ray, magnetic and neutron diffraction measurements the range of solubility in the CrS_xTe_1−x (x = 0−0.2) system has been established and the magnetic phase diagram of the system has been plotted. The decrease of magnetization at low temperature and the additional reflections in the neutron diffraction patterns are associated with the formation of noncollinear magnetic structure which is characterized by the antiferromagnetic component of the magnetic moments. This component has the orthorhombic unit cell with \documentclass{article}\pagestyle{empty}\begin{document}$ a_M = \sqrt {3a_0 } $\end{document}, b_M = a₀, c_M = c₀. The character of the exchange interactions giving rise to this magnetic structure is discussed.     

Periodic Crystallisation of Magnesium Hydroxide in Agar-Agar Gel

Investigations are made to get the experimental conditions for obtaining periodic crystallisation of magnesium hydroxide in agar-agar gel. A detailed study is made on the dependence of the velocity constant (K), the spacing coefficient \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {p = \frac{{x_{n + 1} }}{{x_n }}} \right)'$\end{document} the length of the continuous precipitate and the width of the rings on the concentrations of the inner and outer electrolytes. Using SHINOHARA 's revised coagulation theory, the flocculation value F is calculated. F = Γ + C₃₀, where Γ is the characteristic concentration of the outer electrolyte for which the flocculation starts and C₃₀ is the reduced concentration of the reaction product. The value of the concentration of the outer electrolyte for which the flocculation stops (γ) is calculated. The dependence of F on the concentrations of the reactants is also discussed. Observation of a coneshaped precipitation is also reported.     

Electric conductivity and lattice disorder of PbMoO4 crystals

From differential thermal analysis (DTA), thermal etching, perfectly reversable redox treatments and electric conductivity it is concluded that the Pb/Mo ratio of the PbMoO₄ crystals is always 1 and that phase transitions do not occur. Pb³⁺ ions detectable by an absorption band at 435 nm cause a p-conductivity due to the reaction Pb³⁺ ⇌ Pb⁺⁺ + e⁺. At elevated temperatures the p-conductivity increases with increasing oxygen partial pressure of the surrounding atmosphere. The influence of foreign ions on the concentration of ionic and electronic defects in PbMoO₄, CaMoO₄, PbO, and PbTiO₃ can be explained by an anti-Frenkel disorder of the oxygen ion sublattice. For PbMoO₄ crystals the mobility O⁻ ion vacancies and the free formation enthalpy of anti-Frenkel defects are found to be v_v = \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop - \limits_T^{9160} $\end{document} exp (−1.15 eV/kT) cm² K/Vs and g_AF = 3.6kT −2.2 eV, respectively.     

The Effect of Plastic Deformation on the Real Structure of ZnO Crystals during the Growth Process

The rotational model for ZnO plasticity under the action of concentraion stresses is given on the ground of the real structure analysis (the presence of two scales of the crystal lattice disorientation, a change of the ZnO crystal lattice parameter and the presence of disorientation boundaries of different types). Concentration stresses estimated at the T_gr. \documentclass{article}\pagestyle{empty}\begin{document}$ \tau = G\varepsilon = G\frac{{\Delta a}}{a} \approx 20 $\end{document} MPa exceed the yield point of crystals at T_gr. and may be the cause of rotational plasticity development.     

Neutron diffraction studies of the orthorhombic lattice distortions and magnetic properties of lanthanum manganite obtained under different technological regimes

Neutron diffraction studies have been carried out on two series of lanthanum manganite compositions obtained under different technological regimes. Based on the plot of angle dependence β° characterizing the degree of monoclinic distortions on “tolerance factor” t Mn³⁺ concentration is determined in the compositions obtained by us. With partial oxygen pressure increasing in annealing atmosphere the crystalline transition (orthorhomb-cube) temperature lowers from 583 ± 10°K to 508 ± 10°K. The correlation between magnetic properties of the compositions obtained and the degree of orthorhombic distortions γ′ = \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm b}\sqrt {{\rm 2/c}} $\end{document}\end{document} is established. Neutron diffraction studies of magnetic properties of LaMnO₃ compositions show that with decrease of orthorhombic distortion degree the decrease of antiferromagnetic component and lowering of the Néel point occur, while the ferromagnetic contribution increases and the Curie point rises.     

On the reproducibility of the orientation distribution function of texture samples from pole figures (V). Discussion of the reprojection relationship

The exact solution of the problem \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde P_{hi} (y) \to \tilde f(g) $\end{document} is discussed from the view of the structure of the reprojection relationship and its numerical realization.     

Investigation of the homogeneity of Cu-Ni sintered materials using microprobe

The application of various parameters for the estimation of the degree of homogenization of Cu Ni sinters is investigated. For this purpose specimens were prepared with different Ni contents, different degrees of initial porosity and different sintering periods. Analysis is done by means of point and line technique. The following parameters were used: standard deviation from the mean Ni content, \documentclass{article}\pagestyle{empty}\begin{document}$ S_c = \sqrt {\frac{1}{n}\sum\limits_{i = 1}^n {\left({c_i - \bar c} \right)^2 } } $\end{document}, variation coefficient \documentclass{article}\pagestyle{empty}\begin{document}$ v = \frac{{S_c }}{{\bar c}} $\end{document}, maximum concentration grapient of nickel, \documentclass{article}\pagestyle{empty}\begin{document}$ g = \left({\frac{{dc}}{{dx}}} \right)_{\max } $\end{document} and the relation of the minimum to the maximum Ni concentration in different points of the sinter. – These parameters are enough precise for the representation of the degree of homogenization, but besides this the latter enables to express the homogeneity in the form of a fraction as measure for the homogeneity of a sinter.     

Zum Reflexionsvermögen und Polarisationsverhältnis bei der Röntgenstrahlbeugung am Realkristall (I) Experimentelle Ergebnisse und Vergleich mit der Theorie

Experimental data, a lack of satisfactory theoretical discussion, and some practical problems (application of crystal monochromators, analysis of real structure) as well demand an improvement of the theory of integrated reflectivity, R_i, and of polarization ratio, p, in case of X-ray diffraction in thick real crystals (symmetrical Bragg case). Relatively simple expressions have been obtained concerning the diffraction process in a layer model containing dynamically diffracting mosaic blocks. They fit experimental results, especially the maximum of p at average crystal quality. The theory yields for that maximum p = \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {|\cos 2\Theta |} $\end{document} in case of strong primary and secondary extinction. This is, obviously, in better agreement with experimental work using ordinary monochromator crystals than expressions of the type p = cos² 2 Θ or | cos 2 Θ| or averages of them.     

On the occurrence of polytypism in single crystal CdTe thin films

Cadmium telluride thin films have been found to exhibit polytypism. The polytypes are formed when the as grown amorphous CdTe thin films undergo amorphous to crystalline transformation. The transformed single crystal regions correspond to different polytypes. Besides the well known zinc blende type 3 C cubic phase and less often found wurtzite type 2 H phase, four new polytypes (5 H, 6 H, 6 R and 15 R) the only ones known to-date have been found in the present investigation. In addition to the new polytypes, a new structural variant has also been found. This has the same ‘c’ parameter as that of the 2 H phase but has its ‘a’ lattice parameter as ‘a₀ \documentclass{article}\pagestyle{empty}\begin{document}$ a_{\rm o} \sqrt {3} $\end{document}’ (a₀ being the common lattice parameter of the polytypes). A feasible mechanism making the formation of polytypes intelligible has been suggested.     

Die Molekül- und Kristallstruktur des Morpholyl-pentamethin-merocyanins C9O2NH13

The morpholyl-pentamethine-merocyanine crystallizes within the space group \documentclass{article}\pagestyle{empty}\begin{document}$ P\frac{{{\rm 2}_{\rm 1} }}{{\rm a}} $\end{document} with the lattice constants being a = 13.269 Å, b = 15.232 Å, c = 4.513 Å, β = 94.05°. The bond lengths between the methine-carbon atoms within the pentamethine chain alternate significantly, and thus show a distinct polyenal course. Simultaneously, short C–N (1.339 Å) and short C–O bond lengths (1.224 Å) of the substituents N and O towards the pentamethine chain occur. As with open chained cyanines we also find with this merocyanine a distinct alternation of the valence angles at the methine-carbon atoms. Distances of substituents and alternation of valence angles point to a poylmethinic behaviour of the molecules. The presented merocyanine therefore takes a mean position between a polyenal and a polymethinic behaviour, sharply to be limited by X-ray crystal structure analysis. The experimentally determined geometry of the molecule is compared with quantum mechanical calculations and different structure chemical ideas. On the base of the resonance theory new limiting structures are introduced, the consideration of which enables to give an explanation of the molecule's geometry also in the formalism of mesomerism. The geometry of the chair formed morpholyl ring as well as the packing of the molecules in the crystal bond (intermolecular interaction) are discussed in detail.     

Kinetics of Etching of Dislocations in Ferroelectric Ammonium Hydrogen Tartrate Single Crystals

Ferroelectric crystals of Ammonium Hydrogen Tartrate (AHT) have been synthesised using the controlled reaction between NH₄Cl and (CHOHCOOH)₂ by diffusion process in silica gel medium. (010) cleavages of AHT crystals have been etched in 1.0 M and 1.5 M solutions of SrCl₂ solution. The lateral and normal velocities of the growth of pits were measured at different temperatures. The time dependence of the growth of the pit dimensions is found to be linear, whereas the temperature dependence of the growth of pits is found to be exponential, viz. \documentclass{article}\pagestyle{empty}\begin{document}$ \[V = A\,\exp \left({\frac{E}{{kT}}} \right)\] $\end{document}. The dissolution parameters, e.g. the activation energies and the pre-exponential factors for dissolution along the surface and along the dislocation lines have been computed. It is observed that the activation energy (E₁) of dissolution along [001] direction is found to be greater than the activation energy (E_b) along [100] direction and the implications are discussed.     

The precipitation of sparingly-soluble metal ‘oxinates’ induction periods and nucleation rates

The precipitation of barium, strontium, calcium, magnesium, zinc, cadmium, lead, cobalt, nickel and copper 8-quinolinolates (‘oxinates’) was studied in buffer solutions (pHs from 10 to 4.5) at 22 °C: the metal cation and overall ‘oxinate’ with ‘oxine’ concentrations were varied from 0.0005 to 0.010 M (and saturation rations varied from 3 to 3.000). The induction periods, before the main growth surge, were measured at different metal oxinate concentrations (C) and saturation ratios S = (C)/S · P_r^1/3. Nucleation rates were determined from combined measurements of induction periods and final crystal numbers. Nucleation rates varied with saturation ratios according to the relation \documentclass{article}\pagestyle{empty}\begin{document}$ R_n = k_1 \cdot S^8 {\rm\ nuclei cm}^{ - {\rm 3}} {\rm sec}^{ - {\rm 1}} $\end{document} Induction periods decreased with increasing concentration and supersaturation; over the range t > 3.000 to < 1 sec, . Where t and t were factors that depended on nucleation rates and metal salt solubility. t values decreased and t values increased with decreasing solubility. Precipitation occurred through homogeneous nucleation. Low nucleation rates and prolonged induction periods in solutions of medium to high supersaturation were related to slow rate-determining stages in nucleus formation and to complex formation between metal cation and oxinate anion.     

Concentration Magnetic Phase Transitions in the (La1−xCaxMnO3 System

Comprehensive investigations into crystal structures, electrical and magnetic properties of the (La_1−xCa_x)MnO₃ (x = 0 ÷ 0.6) solid solutions are performed. Two concentration magnetic phase transitions are found: antiferromagnetic-ferromagnetic with x = 0.14 and ferromagnetic (T_c = 150 K) - ferromagnetic (T_c = 260 K) at f = 0.2. It is shown that the first of them is due to the crystal structure O′ O orthorhombic transition, the second - to the increase of ferromagnetic interaction at the expense of additional interaction through conduction electrons. A diagram of the magnetic states for (La_1−xCa_x)MnO₃ at x = 0 / 0.6 is given.     

Heterophase states and a bridging phase in (1‐x)BiScO3 − xPbTiO3

Heterophase ferroelectric solid solutions of (1‐x)BiScO₃ − xPbTiO₃ are studied near the morphotrpic phase boundary (0.60 ≤ x ≤ 0.64). The role of non‐180° domain types of the P4mm and R3m phases in heterophase structures is studied in the context of the phase content. It is shown that the bridging Cm phase coexists with the adjacent phase (either P4mm or R3m), and different variants of an elastic matching ‘single‐domain Cm phase–polydomain P4mm phase’, ‘single‐domain Cm phase–polydomain R3m phase’ and ‘single‐domain Cm phase–near single‐domain R3m phase’ promote the complete stress relief. Based on these concepts and considering a minimum number of the domain types in the coexisting phases, we find a molar‐concentration dependence of the volume fraction of the Cm phase in the heterophase states. A correlation between the predicted volume fraction of the Cm phase and ratios of its unit‐cell parameters is first revealed. The role of the intermediate R3m phase in the phase sequence R3c − R3m − Pm$\overline 3$m and in the stress relief at x = 0.60 is discussed. Good agreement between the predicted and experimental data on the phase content is reached near the morphotrpic phase boundary.     

AlxGa1−xAs LPE growth

Al_xGa_1−xAs LPE growth was studied within the temperature range of 930–900°C with Al concentrations in solutions from 0.04 to 2.4 at.%. AlAs concentration in layers has been shown to grow with the cooling rate increase of solution. Interface and volume nucleation parameter dependence of K_i and K_v and formation time t_f on Al concentration in Ga solution have been found. Addition of Al to Ga solution increases critical values of As supersaturation (supercooling) and, as a result, increase in thickness of Al_xGa_1−xAs layers compared with GaAs layers have been determined in spite of As concentration lowering in Ga solution.     

Crystal size distribution in precipitates

After a short introduction on the principles of nucleation and growth – here especially considering defect crystals – particle size distribution in precipitates is discussed. At first batch crystallization is referred to briefly. The situation in stirred continuous tank crystallizers is investigated in detail. Size distribution is considered in dependence on steady state flow rates of the reacting solutions, residence time of crystals in the tank, resulting in an exponential equation for the number of crystals per unit volume: \documentclass{article}\pagestyle{empty}\begin{document}$ n\left(r \right) = \frac{{\dot n_0 }}{{f\left(s \right)}}e^ - \frac{{vr}}{{V \cdot f\left(s \right)}} $\end{document}. With two and more tanks in series size distribution additionally becomes dependent on the difference of the supersaturations, of the occurrence of nucleation, and of the residence time of crystals in the various tanks. Equations for the size distribution are given for special conditions with two and more tanks in series.     

Doping of PbTe and Pb1−xSnxTe with gallium and indium

Precipitations in Indium and Gallium-doped PbTe, SnTe and Pb_1−xSn_xTe are investigated. The compositions of the precipitated phases are PbGa₆Te₁₀ SnGa₆Te₁₀ and PbIn₆Te₁₀ for binary compounds. For Pb_1−xSn_xTe the precipitated phase composition corresponds to the continuous solid solutions Pb_1−zSn_zGa₆Te₁₀. Basic properties of the new compounds are determined. Their resistivity being of 5 ÷ 6 orders higher than that for Pb(Sn)Te, the anomalous transfer phenomena, observed in highly Ga(In)-doped samples can be explained on the basis of the barrier model.     

Calculations of homogeneous region in Ga1−xAlxAs and GaAs1−xPx ternary solid solutions

Ternary solid solutions of A^IIIB^V compounds are considered as pseudobinary A(x)^IIIB(x)^v compounds, where the behaviour of A(x)^III and B(x)^v pseudoatoms is quite similar to A^III and B^v atoms in a binary A^IIIB^v crystal. Weak dependence of point defect contribution into Gibb's energy of A^IIIB^v crystal on its defect nature, random character of ternary solid solutions of A^IIIB^v compounds allow to use already for binary compounds developed formalism in the determination of component thermodynamic potentials of solid solution. Basing on literature data for the equilibrium solidus of AlAs the approximation for the temperature dependence of thermodynamic potential of an AB quasimolecule in A^IIIB^v crystal is revised. This result together with the well-known parameters for the equilibrium liquidus in Ga–P, Ga–As, and Al–As systems were used for calculations of the nonstoichiometric factor at the boundary of a homogeneous region in Ga_1−xAl_xAs and GaAs_1−xP_x ternary solid solutions. The results are compared with the known literature data.     

Dynamics of structural defects of LPE-grown Gax-In1−xP Layers

The structural properties of epitaxial Ga_xIn_1−xP, LPE-grown on 〈111〉-oriented GaAs-substrate, have been investigated. Two groups of samples have been distinguished with respect to the lattice parameters of the layers (a₁) and the substrate (a_s): group A with a₁ < a_s and Δa/a_s = (0.85 ÷ 2.98)%, and group B with a₁ > a_s and Δa/a_s = (0.11 ÷ 1.98)%. Group A is characterized by a structure, including orthogonal, and slanted at 60° towards the surface, linear dislocations, originating from mismatch ones. Group B is characterized by a segmented-surface structure. The optimum conditions for the growth of GaInP layers on GaAs substrates (initial temperature, saturation and composition of the melt, as well as cooling rate) are discussed on the basis of the data obtained.     

Infrared optical properties of Cu1−xLixSe2 thin films

Infrared absorption spectra of Cu_1−xLi_xInSe₂ thin films are measured at room temperature in the wavenumber range from 100 to 600 cm⁻¹. The spectra exhibit two absorption bands in the wavenumber ranges 200–210 cm⁻¹ and 330–355 cm⁻¹ which are ascribed to vibrational modes due to In Se and Li Se vibrations, respectively. The influence of the phase transition from the chalcopyrite structure to the β-NaFeO₂ structure in the composition range x = 0.5–0.6 on the vibrational characteristics is established and discussed.