The homogeneity region of neodymium- and lanthanum-substituted Bi2Sr2Cu2O8-based solid solutions

This work concerns the determination of the homogeneity region for Bi2Sr2Ca 1-xRxCu2O8+delta and Bi2Sr2-xCaRxCu2O8+delta (R = Nd, La) solid solutions. The phase composition of samples quenched from various temperatures was det ermined by semiquantitative X-ray powder diffraction analysis. In the case of lanthanides with similar or smaller ion radii substituting for alkaline- earth metals (the substitution of neodymium for calcium or of neodymium and /or lanthanum for strontium), the extents of the existence of Bi-2212 solid solutions are almost identical and approximate to x approximate to 0.8. Th is value is governed by the Cu+ ion fraction in crystal positions character istic of Cu2+. In the case of La substituting for Ca, an appreciably narrow er extent of the solid solutions was discovered, x approximate to 0.3, whic h is explained by a larger difference between the Ca2+ and La3+ ion radii.