Complete chemical control of stoichiometry of materials related to high T-c ceramics RBa2Cu3O7-x (R = rare earth)

A simple wet chemical method involving a two-stage complexometric estimatio n of R (R = rare earth) and Ba together with electrogravimetric determinati on of Cu in the same aliquot prepared by dissolving fully or partially heat -treated ceramics of the formulae RBa2Cu3O7-x is described. Combining these results with independent analysis of oxygen/metal (O/M) ratio by an iodome tric procedure reported in the literature, the total composition of samples of RBa2Cu3O7-x (where R = Y, La, Nd, Sm, Dy and Er) could be evaluated wit h the scatter of 0.01 mol of each of the component in the stoichiometric fo rmula with 95% confidence limit. The use of these inexpensive analytical pr ocedures to follow up the changes in the O/M ratio between two stages of he at treatment is also demonstrated. A linear correlation between the unit ce ll volume of RBa2Cu3O7-x with the cube of R3+ radii was also demonstrated e ven though the O/M ratios of the final products in the above six rare earth complexes differed from each other with the maximum difference being 0.04. (C) 1999 Elsevier Science B.V. All rights reserved.