Nanocomposites and nanomaterials

Effects of Hf impurity on the excess conductivity of YBaCuO ceramic samples at temperatures near and above the critical
Vovk R.V.1, Kamchatnaya S.N.2, Litvinov Yurij.V.1, Bohutskyi V.R.2
1 V.N.Karazin Kharkiv National University, sq. Svobody, 4, Kharkiv-61022, Ukraine. 
E-mail: kamchatnayasn@gmail.com
2 Ukrainian State University of Railway Transport, sq. Feuerbach, 7, Kharkov-61050, Ukraine 

One of the most important aspects of the technological application of high-temperature superconducting (HTSC) materials is to ensure the stability of their oxygen subsystem. To the greatest extent, this applies to HTSC compounds, the so-called 1-2-3 or ReBa2Cu3O7-δ system (Re - Y or lanthanides) [1,2].
In this work, the effect of the Hf impurity on the conductivity of YBaCuO HTSC ceramics at temperatures near and above the critical one was researched.
Samples of YBa2Cu3O7 ceramics were synthesized by the interaction of Y2O3, BaCO3 and CuО compounds in the temperature range 750–900°C. The resulting powder was pressed under pressure into discs and baked, followed by cooling to room temperature with intermediate exposures. To obtain samples with the addition of hafnium, a different amount by weight of Hf2O3 was added to the initial mixture.
X-ray and resistive researches of samples of YBa2Cu3O7-δ ceramics have been conducted.
According to the research we can draw the following conclusion. The excess conductivity of YBaCuO samples doped with Hf in a wide temperature range Tf<Т<T* obeys an exponential temperature dependence, and in the case of approaching Tc, it is satisfactorily described within the Aslamazov-Larkin theoretical model. The doping of YBaCuO single crystals with hafnium leads to the effect of expanding the temperature range of the pseudogap mode, thereby narrowing the region of the linear dependence (Т) in the ab plane.

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2.	M.V. Sadovskii, I.A. Nekrasov, E.Z. Kuchinskii, T. Pruschke, V.I. Anisimov // Physic Rev.-2005.- B 72.-P. 155-161.