  A previously unreported ferroelectric phase has been revealed on a highly
homogeneous sample of Pb(Zr0.52Ti0.48)O3 by high-resolution synchrotron x-ray
powder diffraction measurements. At ambient temperature the sample has
tetragonal symmetry (at= 4.037 A, ct= 4.138 A), and transforms below ~250 K
into a phase which, unexpectedly, has monoclinic symmetry (am= 5.717 A, bm=
5.703 A, cm= 4.143 A, beta= 90.53 deg., at 20K). The intensity data strongly
indicate that the polar axis lies in the monoclinic ac plane close to the
pseudo-cubic [111] direction, which would be an example of the species
m3m(12)A2Fm predicted on symmetry grounds by Shuvalov.
