Phase diagram of the relaxor ferroelectric (1 − x)Pb(Mg_1/3Nb_2/3)O₃+xPbTiO₃ revisited: a neutron powder diffraction study of the relaxor skin effect

Abstract

We revisit the phase diagram of the relaxor ferroelectric PMN-$x$PT using neutron powder diffraction to test suggestions that residual oxygen vacancies and/or strain affect the ground state crystal structure. Powdered samples of PMN-$x$PT were prepared with nominal compositions of $x=0.10$, 0.20, 0.30, and 0.40 and divided into two identical sets, one of which was annealed in air to relieve grinding-induced strain and to promote an ideal oxygen stoichiometry. For a given composition and temperature the same structural phase is observed for each specimen. However, the distortions in all of the annealed samples are smaller than those in the as-prepared samples. Further, the diffraction patterns for $x=0.10$, 0.20, and 0.30 are best refined using the monoclinic $Cm$ space group. By comparing our neutron diffraction results to those obtained on single crystals having similar compositions, we conclude that the relaxor skin effect in PMN-$x$PT vanishes on the Ti-rich side of the morphotropic phase boundary.

Keywords:

• relaxors
• PMN
• phase diagram
• morphotropic phase boundary
• skin effect
• neutron diffraction

Acknowledgements

The authors acknowledge useful discussions with J. K. Stalick and S. Ji as well as the support of the National Institute of Standards and Technology, US Department of Commerce, in providing the neutron research facilities used in this work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work at Simon Fraser University was supported by the United States Office of Naval Research (ONR) [grant number N00014-12-1-1045]; the Natural Sciences and Engineering Research Council of Canada (NSERC) [grant number 203772]. Work in the Materials Science Division at Argonne National Laboratory is supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division [grant number DE-AC02-06CH11357]. G.Xu acknowledges support from the Office of Basic Energy Sciences, US Department of Energy [grant number DE-AC02-98CH10886], while C. Stock acknowledges the Carnegie Trust for the Universities of Scotland and the Royal Society.