Effect of zinc doping on the microstructure in YBCO

XRD experiment was conducted on zinc substituted YBCO ceramics in the tempe rature range 90-270K. In undoped or lightly doped samples, the abrupt chang e of lattice parameter at several temperatures and the large average temper ature derivative of lattice parameter, originating from both thermal expans ion and subtle changes of lattice parameter, give evidences for the onset a nd development of CuO5 tilting upon cooling. Such tilting was suppressed by zinc doping and this effect is discussed in favor of the strong and expand ed nature of the disturbance on electronic states created by Zn that is ess ential for tilting mechanism of CuO5 pyramids.