Chlorination of YBa2Cu3Ox compounds solid-gas reaction

An efficient way to influence the superconducting behaviour of the YBa2Cu3Ox compounds is to replace oxygen by another anion having different charge (for instance a halogen), thus changing the copper valence which is an important factor for superconductivity. It has been shown that solid-gas reactions in mild conditions (for instance using NF3 as fluorinating agent) allowed to obtain effectively fluorinated YBaCuO compounds. Some results have also been reported with chlorine, bromine and iodine. Semi-conducting YBa2Cu3O6 becomes superconducting after halogen treatment. We present here preliminary results obtained for three compositions of YBa2Cu3Ox (x=6, 6.7 and 7) treated under Cl2 gas or CCl4 vapors, showing the progressive modification of the superconducting behaviour by chlorination. (orig.)