In-situ neutron diffraction study of Pb(In _1/2Nb _1/2)O ₃-Pb(Mg _1/3Nb _2/3)O ₃-PbTiO ₃ single crystals under uniaxial mechanical stress

In this paper, we report the phase transition behavior of ternary relaxor ferroelectric single crystals of 0.25Pb(In _1/2Nb _1/2)O ₃-0.44Pb(Mg _1/3Nb _2/3)O ₃-0. 31PbTiO ₃ subject to a uniaxial mechanical stress up to 400 MPa. The resultant in situ neutron diffraction data are interpreted in terms of the polarization rotation theory and provide direct structural evidence for the stress-induced polarization rotation pathway deduced from studies of macroscopic physical properties under stress. It is suggested that an intermediate, metastable orthorhombic phase is induced above a critical pressure of ∼75 MPa. This critical stress level appears to be unaffected by sample poling although the ground states (at zero stress) for the poled and unpoled crystals are different. The critical stress level, however, does decrease with increasing temperature. The elastic behavior of the intermediate phases is also studied based on a calculation of the associated lattice strains.