Manufacture of Bi-cuprate thin films on MgO single crystal substrates by chemical solution deposition

Bi2Sr2CaCu2O8 thin films have been deposited on MgO single crystal substrates by spin-coating a solution based on 2-ethylhexanoate precursors dissolved in xylene. Pyrolysis takes place between 200 degrees C and 450 degrees C and is accompanied by the release of 2-ethylhexanoic acid, CO2 and H2O vapour. Highly c-axis oriented Bi2Sr2CaCu2O8 as well as Er-or Ho-doped Bi2Sr2(Ca, Ln)Cu2O8 (Ln = Er, Ho) films were obtained after heat treatment at 840 degrees C in air

Cost-effective isothermal top-seeded melt-growth of single-domain YBCO superconducting ceramics

Abstract In this work, a series of melt processed YBaCuO (YBCO) single-grains have been fabricated by the top-seeded melt growth (TSMG) technique. The melt processing is accepted widely as an effective way to grow bulk, single grain YBCO superconductors; however, this process is extremely complex and every step can affect the final properties of prepared bulk. Therefore, the impact of precursor powder preparation and growth conditions was studied for the first time. Cost-effective in-house made powder and commercially available precursor powders were employed and samples were grown employing top seeded melt growth, following the isothermal and the under-cooling growth techniques. The bulk microstructure including Y2BaCuO5 (Y-211) particle size and distribution, superconducting properties (Tc, Jc) and field trapping potential were investigated. The cost-effective high performance batch processing methodology was optimized. The fabricated YBCO bulks (diameter of 28 mm) exhibited average trapped field of 0.85 T at 77 K. Furthermore, other possibilities to achieve advancement in processing (RE)BCO bulks, are proposed.Czech Ministry of Industry and Trade, project TIP (FR-TI4/184)

Ultraviolet photochemical reaction of [Fe(III)(C2O4)3]3- in aqueous solutions studied by femtosecond time-resolved X-ray absorption spectroscopy using an X-ray free electron laser

Time-resolved X-ray absorption spectroscopy was performed for aqueous ammonium iron(III) oxalate trihydrate solutions using an X-ray free electron laser and a synchronized ultraviolet laser. The spectral and time resolutions of the experiment were 1.3 eV and 200 fs, respectively. A femtosecond 268 nm pulse was employed to excite [Fe(III)(C2O4)3]3- in solution from the high-spin ground electronic state to ligand-to-metal charge transfer state(s), and the subsequent dynamics were studied by observing the time-evolution of the X-ray absorption spectrum near the Fe K-edge. Upon 268 nm photoexcitation, the Fe K-edge underwent a red-shift by more than 4 eV within 140 fs; however, the magnitude of the redshift subsequently diminished within 3 ps. The Fe K-edge of the photoproduct remained lower in energy than that of [Fe(III)(C2O4)3]3-. The observed red-shift of the Fe K-edge and the spectral feature of the product indicate that Fe(III) is upon excitation immediately photoreduced to Fe(II), followed by ligand dissociation from Fe(II). Based on a comparison of the X-ray absorption spectra with density functional theory calculations, we propose that the dissociation proceeds in two steps, forming first [(CO2•)Fe(II)(C2O4)2]3- and subsequently [Fe(II)(C2O4)2]2-

Cost-effective isothermal top-seeded melt-growth of single-domain YBCO superconducting ceramics

In this work, a series of melt processed Y–Ba–Cu–O (YBCO) single-grains have been fabricated by the top-seeded melt growth (TSMG) technique. The melt processing is accepted widely as an effective way to grow bulk, single grain YBCO superconductors; however, this process is extremely complex and every step can affect the final properties of prepared bulk. Therefore, the impact of precursor powder preparation and growth conditions was studied for the first time. Cost-effective in-house made powder and commercially available precursor powders were employed and samples were grown employing top seeded melt growth, following the isothermal and the under-cooling growth techniques. The bulk microstructure including Y 2 BaCuO 5 (Y-211) particle size and distribution, superconducting properties (T c , J c ) and field trapping potential were investigated. The cost-effective high performance batch processing methodology was optimized. The fabricated YBCO bulks (diameter of 28 mm) exhibited average trapped field of 0.85 T at 77 K. Furthermore, other possibilities to achieve advancement in processing (RE)BCO bulks, are proposed

Preparation and characterization of Bi₂Sr₂CaCu₂O_8+δ thin films on MgO single crystal substrates by chemical solution deposition

Bi2Sr2CaCu2O8 thin films have been deposited on MgO single crystal substrates by spin-coating a solution based on 2-ethylhexanoate precursors. Pyrolysis takes place between 200 degrees C and 450 degrees C and is accompanied by the release of 2-ethylhexanoic acid, CO2 and H2O vapour. Highly c-axis oriented Bi2Sr2CaCu2O8 films were obtained after heat treatment at 840 degrees C in air. The highest T-c of 81 K was measured in a 10-layer film. Subsequent post-annealing in Ar and pure O-2 did not improve the superconducting properties of the films and resulted in the appearance of Bi2CaCuO5 or Bi-2(Sr, Ca)(2)CuO6 impurities. (C) 2013 Elsevier B.V. All rights reserved

Aplikace anal�zy Barkhausenova �umu na n�strojov� oceli X210CR12 po semi-solid zpracov�n�

Tato studie popisuje magnetický Barkhausenův šum v nástrojové oceli X210Cr12. Tento proces zahrnuje částečné natavení polotovaru s následným tvářením a kalením. V závislosti na rozložení napětí uvnitř vzorku může být dosaženo vysoké nehomogenity. Signály nedestruktivních Barkhausenových šůmů a extrahované parametry jsou korelovány s konvenčními destruktivními analýzami prováděnými na světelných a skenovacích elektronových mikroskopech, mikrotvrdoměrech a rentgenovými difrakčními analýzami. V důsledku zjemnění matrice došlo ke změně množství zbytkového austenitu, rozdrobení karbidů, Barkhausenův šum byl výrazně snížen a vytvořil dva vrcholy. Konvenční efektivní hodnota Barkhausenova šumu silně koreluje s tvrdostí. Proto by Barkhausenův šum mohl být použit pro sledování nástrojové oceli X210Cr12 po semi-solid zpracování jako technika schopná rozlišit proměnný charakter mikrostruktury (výjádřený ve složitosti tohoto termínu) a stav napětí v oceli.This study reports about magnetic Barkhausen noise in tool steel X210Cr12 after semi-solid forging. Semi-solid subsequent forging involves the partial melting of the workpiece followed by quenching. This process remarkably affects the character of the resulting matrix; stress state; volume of retained austenite; and the size, morphology and distribution of carbides. However, severe non-homogeneity can be found across the sample due to exerted load concentration in the centre of the sample. Non-destructive Barkhausen noise signals and extracted parameters are correlated with conventional destructive analyses performed by metallographic and scanning electron microscopy observations, microhardness and X-ray diffraction measurements. Due to matrix refinement, the volume of retained austenite was altered, carbides were fragmented, Barkhausen noise remarkably decreased and the Barkhausen noise envelope exhibited two peaks. The conventional effective value of Barkhausen noise strongly correlates with hardness. Therefore, Barkhausen noise could be applied for monitoring of tool steel X210Cr12 after semi-solid forging as the technique capable to distinguishing the variable character of the microstructure (expressed in the complexity of this term) and stress state in