Effect of zinc doping on the microstructure in YBCO

XRD experiment was conducted on zinc substituted YBCO ceramics in the temperature range 90-270K. In undoped or lightly doped samples, the abrupt change of lattice parameter at several temperatures and the large average temperature derivative of lattice parameter, originating from both thermal expansion and subtle changes of lattice parameter, give evidences for the onset and development of CuO5 tilting upon cooling. Such tilting was suppressed by zinc doping and this effect is discussed in favor of the strong and expanded nature of the disturbance on electronic states created by Zn that is essential for tilting mechanism of CuO5 pyramids.