Giant piezoelectric response near the uniaxial stress induced tricritical point in Pb(Mg1/3Nb2/3)O3–0.3PbTiO3

We report intriguing piezoelectricity near the uniaxial stress induced tricritical point (TCP) in Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃. Depending on temperature, the transverse compression driven rhombohedral to orthorhombic transition may involve monoclinic and tetragonal states on the polarization rotation path. The TCP occurs on the stress-temperature variable plane when two lines of first-order transitions intersect one line of critical points (LCP). Though the current tricritical point and our previously reported critical end point in the pressure vs. electric field variable plane are of disparate nature, they share a common wedge-shaped feature on the free energy surface. Anisotropic free energy flattening brings about dielectric anomaly and preferential piezoelectric enhancement. Longitudinal piezoelectric constant in the orthorhombic and shear constant in the tetragonal state are remarkably strengthened. Piezoelectric cusps do not diverge on the LCP but exhibit weak divergence at the transition between metastable monoclinic and orthorhombic states.