Abstract
A systematic study has been made of the effect on the structure, electrical conductivity and hole concentration of Bi 2Sr 2CaCu 2O 8+ d resulting from the substitution of rare earths for Ca. The area of the basal plane increased and the c-axis decreased with an increase of rare earth concentration. T c remained at 73 K for x<0.35 and then fell rapidly to below 4.2 K in the range 0.35< x⪕0.6. For x⪖0.6 the resistivity appears to correspond to variable range hopping. The effective Cu-O charge has been determined chemically and the resulting variation of T c with the number of holes per sub cell is in agreement with the behaviour of other systems in which holes occur in Cu-O planes. The smooth transition from superconducting to localised nature is believed to follow from a decrease of the in-plane Cu-O hybridization.
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