Fragile morphotropic phase boundary and phase stability in the near-surface region of the relaxor ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3: [001] field-cooled phase diagrams

摘要

We have examined the effects of field cooling on the phase diagram of the relaxor system (1-x) Pb(Zn1/3Nb2/3)O-3-xPbTiO(3) (PZN-xPT) for compositions near the morphotropic phase boundary (MPB). High-resolution diffraction measurements using Cu K-alpha x rays, which probe approximate to 3 mu m below the crystal surface, were made on field-cooled (FC) single-crystal specimens of PZN-4.5%PT and PZN-6.5%PT under electric fields of 1 and 2 kV/cm applied along [001] and combined with previous neutron diffraction data, which probe the entire crystal volume, for FC PZN-8%PT [Ohwada et al., Phys. Rev. B 67, 094111 (2003)]. A comparison to the zero-field-cooled (ZFC) PZN-xPT phase diagram reveals several interesting features: (1) The short-range monoclinic phase observed in the ZFC state on the low-PT side of the MPB is replaced by a monoclinic MA phase; (2) field cooling extends the tetragonal phase to higher temperatures and lower-PT concentrations; (3) the orthorhombic phase near the MPB is replaced by a monoclinic M-C phase; (4) the vertical MPB in the ZFC phase diagram bends significantly towards the low-PT side in the FC state. These results demonstrate that both the phase stability and the nature of the MPB in PZN-PT within the near-surface regions are fragile in the presence of electric fields.