Thickness-dependent properties of relaxor-PbTiO₃ ferroelectrics for ultrasonic transducers

The electrical properties of Pb(Mg_1/3Nb_2/3)O ₃-PbTiO₃ (PMN-PT)-based polycrystalline ceramics and single crystals were investigated as a function of scale ranging from 500 μm to 30 μm. Fine-grained PMN-PT ceramics exhibited comparable dielectric and piezoelectric properties to their coarsegrained counterpart in the low frequency range (<10 MHz), but offered greater mechanical strength and improved property stability with decreasing thickness, corresponding to higher operating frequencies (>40 MHz). For PMN-PT single crystals, however, the dielectric and electromechanical properties degraded with decreasing thickness, while ternary Pb(In_1/2Nb_1/2)O₃- Pb(Mg _1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT) exhibited minimal size-dependent behavior. The origin of property degradation of PMN-PT crystals was further studied by investigating the dielectric permittivity at high temperatures, and domain observations using optical polarized light microscopy. The results demonstrated that the thickness-dependent properties of relaxor-PT ferro- electrics are closely related to the domain size with respect to the associated macroscopic scale of the samples.