Influence of Sr substitution on the structure, charge distribution, and critical temperature of Y(Ba1-xSrx)(2)Cu4O8 single crystals - art. no. 094518

We have investigated the influence of substitution of Sr for Ba on the stru cture, charge distribution. and T-c in the YBa2Cu4O8 (Y124) compound. Bond valence sum and nuclear quadrupole resonance investigations show that the s ubstitution of Sr causes a redistribution of charge in the structure. The n umber of holes located in plane copper (Cu2) and apical oxygen (O1) increas es. hence the number of holes in chain copper (Cu1) and plane oxygen (O2 an d O3) decreases. A redistribution of holes from Cu1 to O1 and from O2 and O 3 to Cu2 takes place. The literature data for Y123 and the hydrostatic pres sure effect on both Y124 and Y123 compounds show that oxygen doping in Y123 and the pressure effect in Y124 increase the hole number equally on copper and oxygen. Therefore, although the number of holes on copper Cu2 in the C uO2 planes increases with Sr doping in both Y124 and Y123. T-c does not ris e as much as expected from the amount of charge transferred to Cu2. because of their distribution in the CuO2 planes.