Growth of large sized Y Ba2Cu3O7 single crystals using the top seeded melt growth process

Neutron scattering experiments are fundamental to the study of magnetic order and related phenomena in a range of superconducting and magnetic materials. Traditional methods of crystal growth, however, do not yield single crystals of sufficient size for practical neutron scattering measurements. In this paper, we demonstrate the growth of relatively pure, large Y Ba2Cu3O7 single crystals up to 30 mm in diameter using a top seeded melt growth process. The characterization of the microstructural and magnetic properties of these crystals indicates that they contain <2% of impurity phases and, hence, exhibit only weak flux pinning behaviour.

Source:IOPscience

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FeTe0.6Se0.4 bulk single crystals with high critical current densities under magnetic fields

We have fabricated FeTe0.6Se0.4 large-size bulk single crystals with high critical current densities (J c) under magnetic fields. FeTe0.6Se0.4 single crystals were prepared by the melting method with two stage heat treatments. The X-ray diffraction (XRD) analysis and the remanent magnetization method showed that the fabricated bulk crystals are intrinsically single crystals from viewpoint of the critical current flow. Temperature dependence of magnetization revealed that low-T c region exists inside the crystals. The magnetization curves indicated the typical fishtail type, and the magnetic Jc under the magnetic field parallel to the c-axis at 4.2 K achieved 0.36 and 0.2 MA / cm2 at 0 T and 5 T respectively. From the temperature scaling behavior of flux pinning properties we speculated that low-T c regions near excess Fe moderately distributed inside the crystals are dominant pinning centers in high fields at low temperatures.

Source:IOPscience

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Host and defect-related luminescence in Rb2KTiOF5 oxyfluoride crystals irradiated by fast electrons

The paper presents a comparative analysis of RKTF crystals (full name single crystals Rb2KTiOF5), and RKTF + e crystals, single crystals irradiated on a cyclotron by fast electrons Rb2KTiOF5. The crystals were grown by slow solidification method. The study was conducted at a temperature from 7 to 400 K for various types of optical and radiation effects. Spectra of photoluminescence (PL) and X-ray excited luminescence (XRL) in region of 1.5-5.5 eV, time-resolved pulse cathode-luminescence (PCL) spectra, the temperature depending of the XRL, luminescence decay kinetics were studied. Single crystal RKTF are transparent from microwave up to the edge of the long-wave fundamental absorption (near UV range). We detected three luminescence bands for RKTF, in the visible spectral region, that were attributed to radiative annihilation of intrinsic excitons (2.25 eV), recombinaion-type luminescence (2.1 eV) and luminescence of higher TiOF5 complexes (1.9 eV), for all emission bands characterized by great (~1.5-1.8 eV) Stokes shift. The exponential component with lifetime of approximately 19 μs was found in the PCL decay kinetics at 2.25 eV. In the crystal RKTF + e we detected new luminescence bands 2.6 eV and 3.2 eV and the disappearance of the RKTF luminescence bands. Stokes shift of the band 3.2 eV of the RKTF + e crystal is much smaller and is equal to 0.7 eV. Excitation of the band 3.2 eV occurs in the field of crystal transparency, which indicates the defective nature of the glow. PCL decay kinetics at 2.0 and 2.5 eV has a complex nature and consists of at least two components with a life time of 0.5 ms and 6 ms, that significantly more in comparison with RKTF. Irradiation by fast electrons of crystals Rb2KTiOF5 led to entirely new optical properties and suppression of self-luminescence of the crystals.

Source:IOPscience

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In-plane doping profile control of plate-like organic single crystals grown by a method combining electrospray and low vapor pressure liquid film

Although the molecular doping of single crystal organic semiconductors is expected as a key technology that imparts attractive functions in optical and electrical properties, the doping technology in single crystal organic material is still in the initial stages. In this study, doping profile control in the organic single crystal was examined by using an organic single crystal growth method in which a low vapor pressure liquid thin film is used as a crystal growth field and solutes are supplied by electrospray deposition. Steep doping profile control with a transition region of around 1–2 μm was demonstrated using dopants of small molecule red dye and green fluorescent polymer into plate-like single crystal of widegap fluorescent small molecule. We also evaluated the doping profile of the small molecule red dye in microwire-like single crystals of green fluorescent metal complex small molecule.

Source:IOPscience

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The Corrosion of Single Crystals and Recrystallized Single Crystals of Iron and Steel in Citric Acid

Corrosion studies, largely in 0.2M citric acid at 20°C and the boiling point, were made on polycrystalline disks and monocrystalline spheres and disks of Armco iron and type L steel. Preliminary experiments indicated that the (100) face corroded at the slowest rate and the minor faces, of which the (321) is an example, corroded at the most rapid rate. Quantitative measurements were confined to these two crystal faces. The (100) face was cathodic to the (321) face as shown by potential measurements in 0.2M citric acid in the presence and absence of air. The rate of corrosion of the (321) face was approximately twice that of the (100) face on specimens which were chemically polished, electrolytically polished, machined with a sharp lathe tool, or polished with emery paper. The rates of corrosion of the polycrystalline starting material from which the single crystals were prepared were several times greater than those of the single crystals. Conversion of the single crystals to polycrystalline material by heating through the transformation temperature resulted in a considerably increased corrosion rate. In the presence of 40–45 ppm of Sn(II) the rates of corrosion of the single crystals in 0.2M citric acid at the boiling point were reduced greatly and no significant difference between the (100) and (321) faces was observed.

Source:IOPscience

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