Phase diagram and Raman imaging of grain growth mechanisms in highly textured Pb(Mg1/3Nb2/3)O3–PbTiO3 piezoelectric ceramics

Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solution (PMN(1−x)–PTx) ceramics with 0 < x < 1 have been prepared by homoepitaxial templated grain growth (HTGG) using cubic PMN–PT single crystal seeds as templates and nanoparticles for the ceramic matrix. Samples were prepared using the doctor Blade method and sintered in a controlled atmosphere. They were then analysed by DTA, TGA, optical/scanning electron microscopy, Raman spectroscopy and imaging. Relationships between Raman parameters such as band component or area versus composition (x) are proposed. Wavenumber and peak area shifts from the single crystal seed centre to periphery growth are assigned to compositional change. Representative medium to highly textured ceramics with Lotgering factors of ∼0.7 and 0.9 were sintered at 1150 and 1200 °C, respectively, and studied by direct and smart Raman imaging. The Raman peak centre of gravity depends on the solid solution composition whereas peak intensity is correlated to the unit-cell distorsion and related short-range structure. Two different growth mechanisms are observed: below ∼1200 °C, sharp corner and straight edged single crystal seeds develop through a liquid I phase at the crystal/matrix interface; at higher temperatures, the matrix is consumed and crystal growth develops in contact with a liquid II phase, through the help of the high PbO partial pressure. Smart Raman imaging shows that the final composition and structure is very close to that of the matrix. Formation of short-range ordered B/B′ domains is expected. A phase diagram is proposed.