Crystal structure and specific heat of YBa2(Cu1-xZnx)3O7-†(x=0.01 ... 0.1, †=0;0.9)

Abstract Properties of a series of Zn-doped YBa 2 Cu 3 O 7 -samples prepared under identical conditions have been studied by powder neutron diffraction (20 K, 270 K), powder X-ray and electron diffraction (290 K), by measurements of specific heat C p (1.4 K–300 K) and Meissner effect (4 K–100 K). T c decreases linearly at about 10 K /at% Zn. The Meissner signal is still present for high Zn contents. In contrast to this, the transition in C p vanishes at x ≈0.03. Zn is quantitatively dissolved even at x=0.1. The Cu(1)-(chain-) site incorporates about 50% of the total Zn content, while the two equivalent Cu(2)-(plane-) sites contain 25% each. The occupancy of the O(1)-(chain-) site decreases with increasing Zn content according to the approximate formula YBa 2 (Cu 1-x Zn x ) 3 O 7-x/2 . This leads to an almost constant average copper oxidation state, independently confirmed by iodometric titration. Our findings are discussed in terms of a transition to gapless superconductivity upon Zn-doping.