Influence of Zn doping on the thermal expansion of the high T_c superconductor Y₁Ba₂Cu₃O_y

Thermal expansion measurements have been carried out for the Zn-substituted compounds Y₁ Ba₂ (Cu_1-xZn _x)₃O_y (0 ≤ x ≤ 4%) with a high-resolution dilatometer using the three terminal capacitance technique. The present setup is sensitive enough to detect changes in a of about 10 ^-8 K^-1. Results indicate that the jump δα in the coefficient of linear thermal expansion decreases with an increase in Zn content. For x = 1 %, δα decreases by a factor of about five whereas the oxygen content and transition temperature do not change appreciably. There is strong evidence that the temperature dependences of α for compounds with high Zn concentration depend on the conditions of sample growth.