Monoclinic structure of unpoled morphotropic high piezoelectric PMN-PT and PZN-PT compounds

Abstract

Evidences of a monoclinic phase in unpoled $({\mathrm{PbMg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}{)}_{1\ensuremath{-}x}\ensuremath{-}({\mathrm{PbTiO}}_{3}{)}_{x}$ with $x=0.35$ (PMN-PT 35%) and unpoled $({\mathrm{PbZn}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}{)}_{1\ensuremath{-}x}\ensuremath{-}({\mathrm{PbTiO}}_{3}{)}_{x}$ with $x=0.09$ (PZN-PT 9%) are presented from a neutron Rietveld analysis. This monoclinic phase is different from the phase recently evidenced by Noheda and co-workers in ${\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ with $x=0.48$ [B. Noheda et al., Phys. Rev. B. 61, 8687 (2000)] but is identical to the phase observed in poled PZN-PT with $x=0.08$ [B. Noheda et al., Phys. Rev. Lett. 86, 3891 (2001)] by the same authors. The structural resolutions allowed us to compare both structures and to deduce the direction and magnitude of polarization. In PMN-PT 35% and PZN-PT 9% this phase is characterized by a weak value of polarization, a strong deformation of oxygen polyhedra, and weak cationic shifts.