Phase Equilibrium of the Ga–Al–Sb system

Employing the method of liquid-phase epitaxy (LPE) solid-solutions of Ga_1–xAl_xAl_xSb (0 ≦ x ≦ 0.8) have been obtained. The dependence of Sb solubility on Al concentration in the liquid phase at 403°C, 452°C, 500°C has been established. The dependence of AlSb concentration in the solid phase on the composition of the liquid phase has been investigated at 452°C. Using the chemical constants equilibrium method, the phase equilibrium of the Ga–Al–Sb system in the region of liquid phase composition near the Ga-rich corner of the phase diagram has been calculated. The comparison of experimental and calculated data for the liquid and solid phases shows their agreement within the limits of experimental error.     

An Investigation of Molecular Reorientation in Crystalline Pyrazine by Pulse NMR and The Atom-Atom Approximation for Intermolecular Forces

Proton NMR relaxation times (T ₁, at 9.2 MHz and 18.5 MHz, and T ₁ at 18.5 MHz) have been measured for crystalline pyrazine over the temperature range 293 K to the melting point at 327 K. No evidence of a discontinuity in these data is evident at either 29°C or 35°C, where previous workers have found evidence of a phase transition using infrared, Raman, ¹⁴N NQR, calorimetric and other techniques. This result was valid for both unpurified samples and for samples obtained as the result of fractional sublimation. With the assistance of potential energy calculations using the atom-atom approximation for intermolecular forces, the nature of the motional process responsible for the spin-lattice relaxation has been proposed to be an in-plane flip by 180 degrees; this proposal appears to be consistent with all experimental information available for the low-temperature phase stable below 29°C. In addition, the nature of the first phase transition at 29°C has been similarly investigated; it is suggested that this involves an inplane rotation by 90 degrees of just one of the two molecules in the unit cell. Again, this suggestion seems capable of rationalising all available information concerning this transition, although it is possibly not unique in this regard.     

Diffusionsuntersuchungen am System Cu–Ti

As a result of diffusion studies in the binary system of Cu–Ti within a temperature range of 750°C and 850°C the intermetallic phases Ti₂Cu, TiCu, Ti₃Cu₄, Ti₂Cu₃ and Ti₂Cu₇ have been detected by means of electron microprobe analysis. Up to now according to the equilibrium diagram of Zwicker the intermetallic phase Ti₃Cu₄ was reported to be instable only. By the present investigation a time dependence of the width of the total diffusion zone as well as of each of the phases, d∼ √t, has been verified, i.e. volume diffusion is dominating. The chemical diffusion coefficients of all phases have been measured for 750°C, 800°C and 850°C. The partial diffusion coefficients for Cu and Ti in Ti₂Cu₇ for 850°C have also been determined. The chemical diffusion coefficients follow the Arrhenius law, the activation energy Q and the frequence constant D₀ could be calculated.     

Investigations of phase relations in the system CaO?Na2O?K2O?P2O5

The lattice constants of the compound Ca₂NaK(PO₄)₂ have been studied at room temperature using an X-ray powder diffractometer and also in the temperature range from 20 up to 1000 °C by Guinier-Lenné-technology. A hexagonal lattice with the parameters a₀ = 5.4367 Å and c₀ = 7.3125 Å and a cell volume of 187.18 ų has been determined for the high temperature phase, existing from 670 °C upward. At temperatures below 670 °C a superlattice structure is formed by tripling the axis a, a ′, and c so that it results in a hexagonal superlattice structure cell with the lattice constants of a₀ = 16.311 Å and c₀ = 21.939 Å and a cell volume of 5054 ų.     

Calculation of Diffusion-limited Growth of Hg1−x Cdx Te Epilayers on CdTe from Te-rich Melts by Step-Cooling LPE

Calculations of layer thicknesses and composition profiles in Hg_1−xCd_xTe layers on CdTe substrates for the growth from Te-rich melts have been carried out for liquidus temperatures of 460 °C, 480 °C, and 500 °C. This has been made on the basis of the multicomponent diffusion model of SMALL and GHEZ and the solid-liquid phase relation of BRICE . It could be shown that growth velocity increases only slightly with rising liquidus temperature. On the other hand, the interdiffusion velocity of Hg and Cd in the solid increases remarkably at a higher temperature. Therefore, to get layers with a constant x-value a higher supersaturation of the melt is necessary. The x-value decreases with rising supercooling by about 0.003 K⁻¹. To demonstrate the thermodynamically and kinetically advantageous properties of CdTe as substrate material, comparative calculations for a “hypothetical” HgTe substrate have been involved.     

A New Calcium Oxalate Monohydrate Produced by Thermal Dehydration of Weddellite

A high temperature-Guinier photograph of weddellite power showed at 118 °C a transition to a so far unknown phase which transformed to β-Ca(COO)₂ at 135 °C and during cooling down to whewellite at 103 °C. X-ray diffraction studies on single crystals revealed the new phase to have an orthorhombic symmetry with the lattice constant a = 12.088 Å, b = 10.112 Å, c = 14.634 Å, α = β = γ = 90°. There are very simple orientation relations to weddellite: a₁ (wed) ∥ a (new phase), a₂ (wed) ∥ b (new phase), c (wed) ∥ c (new phase). DTA/TG studies showed that the new phase is a calcium oxalate monohydrate.     

Growth of single‐grain GdBa2Cu3O7‐x superconductors by top seeded infiltration and growth technique

The top seeded infiltration and growth technique (TSIG) is an effective way for the preparation of bulk REBa₂Cu₃O_7‐x (RE‐123, where RE denotes rare earth) with finely dispersed RE₂BaCuO₅ (RE‐211) particles compared to the conventional melt growth (MG) method. The nucleation temperature and the ending growth temperature are the most important parameters need to be optimized during the preparation of RE‐123 bulks by the TSIG process. In this paper, the effects of these parameters on the growth of single‐grain GdBa₂Cu₃O_7‐x (GdBCO) superconductors have been investigated experimentally. It is found that the temperature for the growth of single‐grain GdBCO is in the region between 1040 °C and 1015 °C. In addition, the relation between growth rate and supercooling has been investigated in detail. The combined techniques of SEM and EDS were used to study the microstructure of the samples grown at different temperatures. Based on this, a two‐step slow cooling method during the crystallization process is proposed for the fabrication of RE‐123 bulks. Finally, the single‐grain GdBCO samples of the diameters 20 mm and 30 mm were fabricated successfully by the TSIG technique, with the slow‐cooling process in the temperature window 1030 °C–1020 °C for 60 h and 100 h respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Double Salt Formation in the Cu(HCOO)2–Sr(HCOO)2–H2O System

The solubility in the Cu(HCOO)₂–Sr(HCOO)₂–H₂O system has been studied by the method of physico-chemical analysis at 25 and 50 °C. It has been established that two double salts are formed in the system: CuSr₂(HCOO)₆ · H₂O at 25 °C and CuSr(HCOO)₄ · 4 H₂O at 50 °C. The latter salt has not yet been described in the literature. It has been characterized by X-ray powder diffraction and DT and TG analysis. CuSr(HCOO)₄ · 4 H₂O crystallizes in the triclinic system with lattice parameters a = 12.376(6) Å, b = 13.394(4) Å, c = 11.508(6) Å, α = 93.38(3)°, β = 94.01(3)°, γ = 75.04(3)°. Dehydration proceeds in two stages.     

Crystallization of Li2OSiO2 glass studied by positron annihilation

The crystallization of 34 Li₂O65 SiO₂1 P₂O₅ glass has been studied by positron annihilation. The changes in the positron lifetime spectra have been correlated to the magnitude of the amorphous X-ray scattering. A linear relationship has been found for heat-treatment temperatures less than 700°C, above which non-linear phenomena in the lifetime spectra set in. The volume crystallinity reaches a saturation value, which varies from 70% at the heat-treatment temperature of 535°C to 80% at 700°C because of the phase separation. The dimensionality of the crystal growth in this glass is found to be n = 1.5 ± 0.1. The effect of the phase separation on the rate and dimensionality of the crystallization is discussed. The results show that positron annihilation is a sensitive and accurate method to follow crystallization in vitreous materials.     

Temperature Function of Birefringence and Structural Changes in Carbazole Crystal

With a modified quarter-wave Sénarmont compensator, exact measurements of the optical path difference have been carried out in (010) plates of carbazole, C₁₂H₉N, in the temperature range 20 < T < 190°C. At a temperature near 155°C distinct anomaly has been found corresponding to crystal-to-crystal phase transformation. The birefringence changes are discussed in terms of temperature dependence of density and orientation of molecules in the unit cell due to thermal expansion of the crystal.     

Synthesis and phase transitions of oxide-ion conducting compound La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> doped with alkaline metals

The specific features of synthesis, polymorthism, and electric conductivity of oxide-ion conducting compounds La_{2 − x} Me _x Mo₂O_{9 − y} , where Me = Na, K, Rb, or Cs, have been studied. Ceramic samples were obtained by solid-state synthesis in the temperature range of 960–1100°C. The regions where solid solutions exist have been found to depend on the temperature of the sample firing. According to the calorimetric and electrophysical data, the phase transition from the monoclinic phase (α) to the cubic phase (β) in samples doped with potassium and rubidium disappears at x = 0.02 and 0.04, respectively. In these cases the only transition from the cubic β _ms phase to the high-temperature cubic β phase is observed near 450°C. Doping with sodium and cesium does not suppress the α → β phase transition.     

MOVPE growth of spontaneously ordered (GaIn) and (AlIn)P layers lattice matched to GaAs substrates

A systematic study of the metal-organic vapour-phase epitaxial growth of (GaIn)P and (AlIn)P layers deposited on GaAs substrates with (001) and (110) orientation is presented. Special attention has been paid to the growth on (001)-oriented wafers with different misorientations to the growth direction. The influence of the growth conditions on the properties of the epitaxial layers such as lattice mismatch, alloy composition, photoluminescence (PL) wavelength, FWHMs of PL peaks and atomic ordering is discussed. Layers with mirrorlike surfaces and various degrees of order could be deposited at growth temperatures T_g ranging from 595 °C to 750 °C for (GaIn)P and 720 °C to 800 °C for (AlIn)P. In addition to the influence of T_g on the Ga incorporation during the (GaIn)P growth we found the Ga distribution coefficient k_Ga to be affected by the misorientation of the substrates. k_Ga correlates presumably with the number of kinks and steps on the substrate surface. Transmission electron diffraction (TED) and PL investigations show that the degree of order — often described by the ordering paramter η — depends strongly on T_g the ordering is more pronounced when the layers are deposited on substrates misoriented towards the (1 11) lattice plane. Strong ordering has been observed for (GaIn)P samples grown at 680 °C on substrates 2° misoriented towards the [1 10] direction and at 650 °C on substrates 6° misoriented towards the same direction. For the (AlIn)P samples striking ordering has been found when they were grown at 720 °C.     

Investigation of structural transformations in Cu2Se

Structural transformations in Cu₂Se have been studied by the method of hightemperature roentgenography. From a diffraction record of reflection angles and from a Debye-powder pattern the unit-cell parameters of a rhombic α-modification have been calculated at temperatures of 25, 50, 100, and 132 °C. Using the diffraction line (027) disappearing under the α → β transformation and appearing again in the course of the inverse β → α transformation it has been found that the equilibrium temperature between the α- and β-modifications is T₀ = 134 ± 0.5 °C. The unit cell parameter of a hightemperature face-centered cubic β-modification at temperatures of 150, 200, 250, and 300 °C also has been determined. In the course of mutual transformations a rigid orientational linkage has been found to exist between the α- and β-modifications. It has been discovered that when the multiplicity of α → β and β → α transformations n reaches a value of approximately 30, a β-Cu₂Se → Cu₂–_xSe transformation (where x = 0.20) takes place which is not followed by an inverse transformation.     

GeO2 based high k dielectric material synthesized by sol–gel process

Recently, there has been lot of research on new high dielectric constant (high k) materials for use in future generations of ultra-large scale integrated circuits (ULSI). There are number of requirements for the new high k materials, such as high dielectric constant, thermal stability (400 °C or higher), high mechanical strength, and good adhesion to neighboring layers. Keeping in view the properties required for the replacement of existing SiO₂ dielectrics, new high k dielectric material based on GeO₂ has been synthesized. Polycrystalline GeO₂ thin films have been deposited by simple, and cost effective sol–gel spin coating process. The obtained xerogel films of germanium oxide have been annealed at 400 °C, 600 °C and 800 °C for 3 h in argon atmosphere. Elemental composition, morphology, and phase analysis have been measured by employing X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction techniques, respectively. The formation of the hexagonal GeO₂ phase at and above 400 °C has been reported. The composition of the annealed films have been measured and found to be 68 at.% of O, 32 at.% of Ge for GeO₂, which are close to the stoichiometry of the GeO₂.     

The Description of the Isothermal Decomposition Processes in Al?Sc Alloys by means of Electric Resistivity Measurements and TEM Investigations

The decomposition behaviour of two AlSc alloys (c_Sc = 0.18; 0.36 at.%) after direct quench to room temperature and subsequent ageing at temperatures in the range 200 °C ≦ T_a ≦ 550 °C was investigated by means of isothermal resistivity measurements and TEM. In the temperature range 325 °C ≦ T_a ≦ 400 °C both alloys show independent of the Sc content an “inversion” of the decomposition kinetics, obviously caused by the transition of the coherent into the incoherent Al₃Sc phase.     

Square-Planar trans-Bis-(1-p-n-octylphenylbutane-1,3-dionato) copper (II), a New Compound Exhibiting Three Kinds of ‘Double Melting’ Behaviour

The new compound, bis-(1-p-n-octylphenylbutane-1,3-dionato) copper(II) has four polymorphs, C¹ (m.p. 96°C), all having the same squareplanar trans structure. C¹, C^a, and C^m exhibit ‘double melting’ behaviour, i.e., they melt at their was observed only on very rapid heating, while that of C^a and C^m only on slow heating. Slow solid-solid phase transition from C¹ to C^h was observed at ca 50°C. Each polymorph could be obtained as a stable form at room temperature and gave a quite different X-ray diffraction powder pattern. The interrelationships of the four forms have been clarified by differential scanning calorimetric and micriscopic measurements. When the melt of the complex is rapidly cooled, it converts into a glassy state, which is stable at room temperature. The glass transition temperature T₈ and the crystallizing temperature T_e are very close to each other at 52.5°C and 58.0°C, respectively.     

Contribution to the Ti‐Bi phase diagram

The system Ti‐Bi has been investigated by solid/liquid diffusion couples at 400, 500, 600 and 700 °C. Indication that the growth rate of the diffusion layers at 500 °C is linear has been found, with a growth constant of around 5 × 10^–11 m.s^–1. The existence of the Ti₂Bi phase has been confirmed. Some formerly unknown binary phases (TiBi, Ti₂Bi₃, TiBi₂) have been observed. The phase TiBi is, probably, identical with Ti₈Bi₉ reported previously. All intermediate phases suffer air corrosion, but in various degrees. A tentative variant of the Ti‐Bi phase diagram, including the newly found compounds, has been constructed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the formation of quasicrystalline Al<Subscript>70</Subscript>-Pd<Subscript>20</Subscript>-Re<Subscript>10</Subscript> phase in situ during annealing

The change in the phase composition of thin-film layered AlPdRe nanostructures during annealing, which led to the formation of a quasicrystalline layer, has been studied in situ. It is shown that the Al₃Pd phase is formed at a temperature above 260°C, which transforms into the AlPd phase at 580°C, and the icosahedral quasicrystalline Al-Pd-Re phase is formed at 680°C.     

Interactions between YBa2Cu3O7-x and K2Co3

The interactions between YBa₂Cu₃O_7-x and K₂CO₃ have been studied using thermochemical methods, isothermal annealing of diffusion pairs, optical microscopy, X-ray diffraction, and microprobe analyses. The experiments have shown existence of solubility of YBa₂Cu₃O_7-x or its constituents in both solid and liquid K₂CO₃. The barium ions are preferably dissolved in K₂CO₃, whereas potassium cations do not enter massively into the bulk of the YBa₂Cu₃O_7-x-phase. A eutectic-type phase diagram is supposed for the system K₂CO₃–YBa₂Cu₃O_7-x. The so called “green phase” Y₂BaCuO₅ and a K–Cu–O compound have been found in the contact zone at 813 °C while a “black phase” layer with nominal composition Y_1.6Cu_2.8O_5.4 has grown at 707 °C.     

The crystal structure of α‐SrGaBO4

A new compound α‐SrGaBO₄ has been synthesized by solid state reaction at high temperatures, and its structure has been solved by direct methods from powder X‐ray diffraction. α‐SrGaBO₄ has an orthorhombic system, Pccn space group, with lattice parameters a = 15.3154(7) Å, b = 8.9186(4) Å, c = 5.8130(3) Å, and Z = 8. The structure consists of infinite chains run parallel to the c axis and built up of GaO₄ tetrahedral and BO₃ triangles. The basic unit of these chains is a six ‐ membered Ga₂BO₈ ring formed by two GaO₄ tetrahedra and one BO₃ triangles. The Sr atom is bonded to eight oxygen atoms. The strontium atoms serve to hold the chains together through co‐ordination with oxygen atoms. DTA curve of noncrystalline glassy SrGaBO₄ was discussed. The XRD results show no phase transition occurs between ‐173 °C and 127 °C. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)