AN ANALYSIS OF CHARGE-CARRIERS DISTRIBUTION IN RBA2CU3O7 USING THE CALCULATION OF BOND VALENCE SUMS

The distribution of charge carriers in the RBa2Cu3O7 structure between Cu(2)O-2 planes and Cu(1)O chains was studied using the calculation o f bond valence sums with the strain correction taken into account. Wit h a growth of the R3+ ionic radius, h(pl) decreases and h(ch) increase s almost linearly. The optimum value of the hole concentration in Cu(2 )O-2 planes was found to be about 1/4. The result implies, that RBa2Cu 3O7 phases with R = La, Nd, are underdoped and those with R = Y, Sm-Lu are overdoped. A model of possible real-space charge carrier ordering in Cu(2)O-2 planes of RBa2Cu3O7 with the optimum hole concentration w as proposed. (C) 1997 Elsevier Science B.V.