Analysis of YBCO

The most important parameter is the value of % in formula which gives the hole concentration. For simplicity this is represented as the Cu(III) content. The simplest analytical method is iodometric. A weight of the sample is dissolved in 1 M HCl in air, when Cu(III) is reduced by water to Cu(Il). Then the Cu originally present and Cu so formed liberate iodine when treated with K1 solution. The iodine is then titrated with 

The combined determination of total Cu, Ba and Y is possible by dissolving a weight of powder in 1 M HCl. On treatment with sulphuric acid, barium sulphate precipitates and weighed. The filtrate containing Cu and Y is then treated with S02/SCN solution when Cu is precipitated as thiocyanate and weighed. The filtrate contains Y which is determined by EDTA titration or assayed spectrophotometrically. 

Add to the filtrate 30 cm of freshly prepared saturated sulphur dioxide solution in the fume cupboard. Heat to near boiling and add 2.5 cm of 10% potassium or ammonium thiocyanate solution, slowly with constant stirring. Allow to cool and stand, preferably overnight. Filter, wash and dry as in Sec. 16.4.1, collecting the filtrate in a clean evaporating basin. 

Although Y in aqueous solution can be determined by EDTA titration, Cu ions have to be removed by a lengthy procedure. However, the organic dye arsenazo (6-phenylazo-3-arsonophenylazochromotropic acid) forms a violet complex witii Y(III). 

Evaporate the filtrate from the previous operation (after precipitating Cu) to dryness, pipette 5.0 cm cone. HCl, to the residue, warm to dissolve. After cooling, add 0.3 cm  

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In fig.l there are presented results of detailed analysis of resistive behavior for YBCO single crystal in the model where total resistivity ptot is... 

In order to provide the opportunity for a direct analysis of structure-property correlations, measurements of structure and properties need to be performed on the same sample. Recent work in our laboratory has focused on the study of 45°/[001] tilt grain boundaries in YBCO [10.17, 10.19, 10.58-10.60]. Thin films were deposited epitaxially, using several techniques and deposition conditions. In each case grain boundaries were introduced into predetermined patterns suitable for electrical characterization. The individual thin-film bi-epitaxial grain boundary junctions then were electrically characterized by using... 

Faiz et al. (1996) have applied micro-PIXE analysis to study solute distributions in a single crystal sample of YiBa2Cu307 5 high temperature superconductor (YBCO) of dimensions 1.3 mm x 1.5 mm x 75 pm. It contained a small secondary crystal overgrowth of dimensions 340 x 340 x 100 pm3. The interface region between the smaller crystal and the base crystal was covered with a material which appeared to be residual flux. The instrument employed a 2.5 MeV focused proton beam of about 4 pm resolution, which could scan an area of 500 x 500 pm2 on the sample surface. The microbeam current was kept low (typically about 30 pA) to avoid any damage to the sample. 

A recent preprint [38] dealing with the chain buckling distortion in the high temperature superconductor, YBCO, is an example of such an analysis and which urgently calls for a new approach to the problem. Our method should be a viable alternate in the near future in addressing such problems. For this we need to provide the functional of two variables, the electron density and the ion coordinate. 

The simplest methods of HTSC analysis are based on the determination of the products of sample dissolution in acidic media. Potentiometric, amperometric, or coulometric titrations are frequently used (mainly for YBCO ceramics [525-527] and their analogs with other rare-earth elements [528, 529], and also for BSCCO [530]). We note particularly the method of potentiostatic coulometric analysis [531], which allows one to analyze thallium cuprate samples over a wide range of the Tl/Cu ratio, and also the method of flow-through coulometry for determining the effective valence of copper [532]. The polarographic determination of Cu content in the samples obtained by dissolving HTSCs in concentrated alkaline solutions with special... 

For application to YBCO, it has been pointed out that bond-valence calculations are empirical and cannot be used to determine the valences of the elements involved to better than around 10% [11.43]. However, in the case of the boundary structures observed here, the atomic positions can only be determined with an accuracy of 0.1 A, making any errors induced by the bond-valence sum analysis second order. As such, the bond-valence sums can be used to indicate positions where the valence of the elements involved changes considerably, although relating the magnitude of the change to properties must be approached with care. 

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