Influence of Adsorbed Organic Molecules on the Critical Parameters of HTSC Ceramics. Part I. YBa2Cu3O7-x Treated with Phenidone and Hydroquinone
Materials Research Innovations
, E-ISSN: 1433-075X
Makarshin Lev L.
Andreev Dmitry V.
Golikova Natalya A.
Parmon Valentine N.
Boreskov Institute of Catalysis, pr. Akad. Lavrentieva 5, Novosibirsk 630090, Russia
A modification of high-temp. superconducting materials with the use of org. compds. is the issue of the day. The modification makes it possible to change superconducting properties in a controlled fashion, to protect ceramic superconducting materials from the action of the atm. as well as to elucidate the role of cationic and anionic subsystems in the appearance of the superconducting state in superconducting cuprates. The influence of org. compds. on superconducting properties was first studied using low-temp. superconductor metallic films by adsorption of org. compds. of different natures. The increase or decrease of the temp. of the superconducting transition, Tc, was assocd. with electron-donor properties of the adsorbed mol. The treatment of YBa2Cu3O7-x powder by org. donor-acceptor electron transport systems (DMF - CCl4, dimethylsulfoxide - CCl4, etc.) is described in Nifontova et al.. After this treatment, the labile subsurface oxygen in the superconductor's lattice appears to be removed and more perfect and structured cryst. layers are displayed. In this connection it is interesting to study the effect of adsorbed org. mols. with a reducing ability on the superconducting properties of ceramics YBa2Cu3O7-x. A striking example of such org. compds. is hydroquinone (p-dihydroxybenzene) and phenidone (1-phenyl-3-pyrazoline). The YBa2Cu3O7-x powder was treated in hermetically sealed glass ampoules with a definite concn. of hydroquinone or phenidone in pure dried benzene. After the treatment during a definite period, the powder sample was used in the magnetic measurements. The testing expts. showed that the superconducting properties of the ceramics were maintained after its soaking in pure benzene. According to the magnetic measurements, superconducting properties of ceramics YBa2Cu3O7-x change after their treatment with a hydroquinone or phenidone soln. in benzene (10-3 mole/L) at room temp. Figure 1 shows the magnetic susceptibility vs. temp. of the initial sample and of the sample treated with phenidone and hydroquinone for 1 day. After the treatment, Tc increases almost immediately by ca. 3 K. But the value of the abs. magnetic susceptibility significantly decreases, esp. when the sample is treated with hydroquinone. Such a magnetic response suggests a degrdn. of the superconducting properties of YBawCu3O7-x, which is caused by the redn. of either the superconducting phase fraction or the transport crit. current. To understand the mechanism of the obsd. phenomenon, the ceramics were addnl. studied by X-ray diffraction anal., optical and IR spectroscopy, and thermal gravimetry. The X-ray diffraction anal. showed that the sample microstructure has changed due to the increased defectiveness of the material, which may be accompanied by the formation of microcracks and small particles of a new phase. The IR spectroscopy substantiates the occurrence of chemisorption of hydroquinone on the ceramics surface accompanied by a formation of a strong complex with charge transfer or by a chem. reaction yielding new adsorbed mols. On the basis of the thermogravimetry data, we conclude that the adsorbed hydroquinone reacts with the weakly bound oxygen of the superconducting ceramics. Thus the modification of YBa2Cu3O7-x ceramics is assocd. with the redn. of the weakly bound oxygen and the formation of the copper cations in the oxidn. state +3.