Low-alloyed molybdenum single crystals: preparation, structure and properties

Investigation concerns the method of preparation of low-alloyed molybdenum single crystals directly from molybdenum rods and wire, rod or foil containing the appropriate alloying metal, excluding the stage of pre-fusion of the components in an arc furnace, which is more economical than traditional method. In this way Mo-W, Mo-Ta (1,5 wt.% alloying elements of each) and Mo-Re (2 and 3 wt.%) single crystals were prepared by electron-beam zone melting. Authors discuss in more detail the structure and structural parameters of prepared single crystals. Some structural features of Mo-2 wt.% Re and Mo-3 wt.% Re single crystals are explained. Moreover the coefficient thermal linear expansion (CTLE) was measured for Mo-Re single crystals. As shown the proposed method ensures the preparation of single crystal even in single stage melt. The structural imperfections may be removed by following re-melting.

Source:IOPscience

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A novel in situ method for simultaneous growth of smart material single crystals and thin films

Development of a novel in situ method for simultaneous growth of single crystals and thin films of a smart material spinel is achieved. Material to be grown as metal-incorporated single crystal and thin film was taken as a precursor and put into a bath containing acid as a reaction speed-up reagent (catalyst) as well as a solvent with a metal foil as cation scavenger. By this novel method, zinc aluminate crystals having hexagonal facets and thin films having single crystalline orientation were prepared from a single optimized bath. Properties of both crystals and thin films were studied using an x-ray diffractometer and EDAX. ZnAl2O4 is a well-known wide bandgap compound semiconductor (Eg = 3.8 eV), ceramic, opto-mechanical and anti-thermal coating in aerospace vehicles. Thus a space_ gmr technique was found to be a new low cost and advantageous method for in situ and simultaneous growth of single crystals and thin films of a smart material.

Source:IOPscience

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Refined crystal structures and phase transitions in 0.24Pb(In1/2Nb1/2)O3–0.43Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystal

Local lattice structures of 0.24Pb(In1/2Nb1/2)O3–0.43Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (0.24PIN–0.43PMN–0.33PT) single crystal have been investigated by Micro-Raman spectroscopy. A total of 12 Raman active modes were ascertained using the Gauss–Lorentzian line shape approximation, which confirmed that the 0.43PIN–0.26PMN–0.33PT single crystal has monoclinic symmetry at room temperature. The phase transitions were investigated by analyzing the temperature-dependent relative dielectric permittivity of both poled and unpoled 0.43PIN–0.26PMN–0.33PT single crystals measured upon heating. The monoclinic–tetragonal phase transition occurs at TM–T = 82 °C, and the Curie temperature is 199 °C. The splitting of (200) and (002) peaks in detailed X-ray diffraction spectra in the 2θ range of 44.6–45.2° during heating from room temperature to 200 °C was also studied. For a sample being poled along [111]c pseudo-cubic direction, several sharp peaks arise in the thermally stimulated depolarization current from 67 to 82 °C with the main peak occurs at 67 °C, which indicates that the depolarization temperature is 15 °C lower than the monoclinic to tetragonal phase transition and there are coexistence of monoclinic and rhombohedral phases in the [111]cpoled single crystal.

Source:IOPscience

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Influence of Mn doping on CuGaS2 single crystals grown by CVT method and their characterization

1 and 2 mole% of Mn doped CuGaS2 (CGS) single crystals were grown by the chemical vapour transport (CVT) technique using iodine as the transporting agent. The analysis of the single crystal x-ray diffraction data suggests that the doping of 1 and 2 mole% Mn in the CGS single crystal does not affect the tetragonal (chalcopyrite) crystal structure. The optical absorption spectrum shows that the Mn ion induces a very strong absorption band in the UV–visible–near IR regions. The values of the crystal parameter (Dq) and the Racah parameter (B) calculated from the absorption spectra show d electron delocalization in the host crystal CGS. Room temperature photoluminescence spectra of undoped CGS only exhibited a band–band emission. But 1 and 2 mole% Mn doped CGS single crystals show two distinct CGS and Mn2+ related emissions, both of which are excited via the CGS host lattice. Raman spectra of 1 and 2 mole% Mn doped CGS single crystals exhibit a high intensity peak of the A1 mode at 310 cm−1 and 300 cm−1, respectively. EDAX, optical absorption and Raman spectrum studies reveal that Mn2+ ions are substituted in the Ga3+ ions and incorporated into the CGS lattice. The magnetization of Mn doped CGS single crystals was measured as a function of the magnetic field and temperature. Paramagnetic behaviour typical of spin S = 5/2 expected for Mn2+(d5) magnetic centres was observed in the temperature range 2 K < T < 300 K. In Mn doping, the increase in bulk conductivity of the Mn doped CGS single crystals at room temperature indicates an increase in the hole concentration.

Source:IOPscience

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