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1

Structure, conformation and hydrogen bonding of two amino-cycloalkanespiro-5-hydantoins

100%

Todorov P., Petrova R., Naydenova E., Shivachev B.

Open Chemistry

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2009

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vol. 7

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issue 1

14-19

EN

The crystal structures of 3-amino-cycloheptanespiro-4′-imidazolidine-2′,5′-dione (I) {systematic name: 3-amino-1,3-diazaspiro[4.6] undecane-2,4-dione} and 3-amino-cyclooctanespiro-4′-imidazolidine-2′,5′-dione (II) {systematic name: 3-amino-1,3-diazaspiro[4.7] dodecane-2,4-dione}, have been determined. In both compounds the polar hydantoin groups cause molecules to aggregate via N-H...O and N-H...N interactions, forming a layer structure, in which the cycloalkane rings project outwards from the central, more polar, region. The observed molecular structure is compared with that calculated by density functional theory methods. [...]

2

Synthesis and superconducting properties of Nd0.33Eu0.08Gd0.58Ba2Cu3Oz materials

88%

Stoyanova-Ivanova A., Terzieva S., Shivachev B., Mikli V., Vladimirova L.

Open Physics

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2008

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vol. 6

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issue 1

76-79

EN

We have studied the effect of the ratio of different rare-earth element on the superconducting properties and phase formation of (Nd0.33Eu0.08Gd0.58)Ba2Cu3Oz ceramic. Bulk NEG samples were prepared using the solid-state reaction process. The superconducting transition for Nd0.33Eu0.08Gd0.58Ba2Cu3Oz is T c ≈90 K and the value of the critical current density (J c) is 13.9 A/cm2 at 77 K under zero magnetic fields. This value is twice as high when compared with the (J c) value of YBCO systems (J c = 7.31 A/cm2). The obtained bulk sample was used for the production of superconducting Ag-sheathed tapes by OPIT method including hot rolling. The critical current density of the obtained tape (337 A/cm2) is one order higher than the one of the bulk sample.

3

Microstructure and thermal properties of quasi-equal rare earth substitution Y0.5Gd0.5Ba2Cu3O6.94 superconductor

76%

Terzieva S., Stoyanova-Ivanova A., Shivachev B., Terzijska B., Zaleski A., Misiorek H., Mikli V.

Open Physics

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2009

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vol. 7

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issue 1

84-88

EN

Sintering effects in YBa2Cu3Oz samples with quasi-equal rare earth substitution have been investigated. It has been shown that the Y-123 type compound can be formed when gadolinium is partially substituted (in this case 50% atomic substitution) for yttrium. The superconducting compound was obtained by the optimized ceramic method, including solid-state reaction, melting and sintering, controlled by X-ray diffraction. The microstructure was investigated by SEM and energy dispersive X-ray analyses. An AC susceptibility measurement has shown that T c =93 K. Temperature-dependece of the thermal conductivity (4.5–300 K) of the polycrystalline Y0.5Gd0.5Ba2Cu3O6.94 sample was also measured.

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1 Naydenova E.

1 Petrova R.

1 Terzijska B.

1 Todorov P.

1 Vladimirova L.

1 Zaleski A.

Structure, conformation and hydrogen bonding of two amino-cycloalkanespiro-5-hydantoins

Synthesis and superconducting properties of Nd0.33Eu0.08Gd0.58Ba2Cu3Oz materials

Microstructure and thermal properties of quasi-equal rare earth substitution Y0.5Gd0.5Ba2Cu3O6.94 superconductor