High-resolution synchrotron XRD study of Zr-rich compositions of   Pb(Zr_xTi_1-x)O_3 (0.525\leq x \leq 0.60): evidence for the absence of the   rhombohedral phase
  Results of Rietveld analysis of the synchrotron XRD data on Pb(Zr_xTi_1-x)O_3 (PZT) for 0.525\leqx\leq0.60 are presented to show the absence of rhombohedral phase on the Zr-rich side of the morphotropic phase boundary (MPB). Our results reveal that the structure of PZT is monoclinic in the Cm space group for 0.525\leq x\leq 0.60. The nature of the monoclinic distortion changes from pseudo-tetragonal for 0.525\leqx\leq0.54 to pseudo-rhombohedral for x>0.54. 
Akhilesh Kumar Singh, Dhananjai Pandey, Songhak Yoon, Sunggi Baik and   Namsoo Shin