  The structural phase transformations of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3
(PMN-30%PT) have been studied using x-ray diffraction (XRD) and neutron
scattering as a function of temperature and electric field. We observe the
phase transformational sequence (i) cubic (C)-> tetragonal (T)-> rhombohedral
(R) in the zero-field-cooled (or ZFC) condition; (ii) C->T-> monoclinic (MC)->
monoclinic (MA) in the field-cooled (or FC) condition; and (iii) R->MA->MC->T
with increasing field at fixed temperature beginning from the ZFC condition.
Upon removal of the field, the MA phase is stable at room temperature in the FC
condition, and also in the ZFC condition with increasing field. Several
subtleties of our findings are discussed based on results from thermal
expansion and dielectric measurements, including (i) the stability of the MA
phase; (ii) a difference in lattice parameters between inside bulk and outside
layer regions; and (iii) the diffuse nature of the MA and MC phase transition.
