Y. Zhang Iono-covalent theory applications (26)
American Huilin Institute http://www.amhuilin.com/
The crystal structure of the high-temperature superconductors (HTSC) and compositional parameters have been correlated with the composition (Bi1-y Pby)2Sr2(Ca1-xRx)Cu2O2+d by Ilyushin et al : “The magnitude of ¶c/¶(x) gives additional evidence that for an explanation of the influence of substitutions of elements on the unit cell parameters one must take some additional factors beyond the ionic radii of the elements into consideration. For the coordination number 8, the ionic radii rca2+ = 1.12A, and ry3+ = 1.019A (Shannon 1976). Hence, the decrease of the double radius of element in the Ca site is 2rca+y » 0.2A for the complete substitution of Ca with Y, which is 3.5 times less than the ï¶c/¶(x)ï. One such factor can be the difference in electronegativities X of corresponding ions, Xca2+ < X y3+ (Zhang 1982) , and hence, the contribution of the difference in X in the change of the interlayer distance has the same sign as that of the difference of the ionic radii.”
 A.S. Ilyushin, L. Shi, L.I Leonyuk, B.M.Mustafa, I.A.Nikanorova,. S.V. Red’ko, Y. Jia, A.G.Vetkin, G. Zhou, I.V. Zubov, J. Mater. Res., 1993, Vol. 8, No. 8, Aug, 1791-1797.
 Y. Zhang,, Inorg Chem., 1982, 21, 3886.