A ferroelectric monoclinic phase of space group Cm (MA​ type) has been
discovered in 0.65Pb(Mg1/3​Nb2/3​)O3​-0.35PbTiO3​ by means of high
resolution synchrotron X-ray diffraction. It appears at room temperature in a
single crystal previously poled under an electric field of 43 kV/cm applied
along the pseudocubic [001] direction, in the region of the phase diagram
around the morphotropic phase boundary between the rhombohedral (R3m) and the
tetragonal (P4mm) phases. The monoclinic phase has lattice parameters a = 5.692
A, b = 5.679 A, c = 4.050 A and β = 90.15∘, with the bm​-axis
oriented along the pseudo-cubic [110] direction . It is similar to the
monoclinic phase observed in PbZr1−x​Tix​O3​, but different from that
recently found in Pb(Zn1/3​Nb2/3​)O3​-PbTiO3​, which is of space
group Pm (MC​ type).Comment: Revised version after referees' comments. PDF file. 6 pages, 4
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