Structural transitions in [001]/[111]-oriented 0.26Pb(In _1/2Nb_1/2)O₃-0.46Pb(Mg_1/3Nb _2/3)O₃-0.28PbTiO₃ single crystals probed via neutron diffraction and electrical characterization

We report changes in the metric symmetry of unpoled and electrically poled single crystals of 0.26Pb(In_1/2Nb_1/2)O₃-0. 46Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃, as revealed by neutron diffraction in conjunction with electrical measurements. The unpoled crystals show relaxor characteristics and an average rhombohedral symmetry that persists from ambient temperature up to the Curie temperature of ∼165 °C. Poling along a [111] direction enhances the rhombohedral distortion away from cubic metric symmetry but appears not to induce any monoclinic phases. By contrast, the poled [001]-oriented crystal has orthorhombic (or monoclinic M_C) metric symmetry at 25 °C. An intermediate transition to a metrically tetragonal phase around 120 °C is confirmed for both poled crystals.