Pressure-composition phase diagram of the Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3) solid solutions

摘要

We combine high-pressure x-ray diffraction, high-pressure Raman scattering, and optical microscopic methods to investigate a series of PMN-xPT solid solutions (x(velence)0.2, 0.3, 0.33, 0.35, 0.37, 0.4) in diamond anvil cells up to 20 GPa at 300 K. The Raman spectra show a new peak centered at 380 cm~(-1) above 6 GPa for all samples, consistent with previous observations. X-ray diffraction measurements are consistent with this spectral change indicating a structural phase transition. For example, we find that the triplet at the pseudocubic [220] Bragg peak merges into a doublet above 6 GPa. The analyzed results indicate that the morphotropic phase boundary (x(velence)0.33 to 0.37) with monoclinic symmetry persists up to 7 GPa. The pressure dependence of ferroelectric domains in PMN-0.32PT single crystals was observed with a polarizing optical microscope. The domain wall density decreases with pressure and the domains disappears at modest pressure of 3 GPa. This indicates that the high pressure phase of PMN-PT is not a macroscopic polar state. We suggest a phase diagram for the PMN-xPT solid solutions.