Novel Piezoelectric Single Crystals PMN-PT And Their Applications In Medical Ultrasonic Transducers

The piezoelectric materials most commonly used in transducers for medical imaging are soft piezoelectric ceramics such PZT-5A and PZT-5H. However they are polycrystalline ceramics, brittleness and temporal aging, the operating frequency is finite and some parameters are variable with the going of time and changing of environmental temperature which will impede their regular operation. Recently, relaxor ferroelectric single crystals of (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (hereafter as PMN-PT) and(1-x)Pb(Zn_1/3Nb_2/3)O₃-xPbTiO₃(hereafter as PZN-PT) are provided with superior piezoelectric properties than Pb(Zr_1-xTi_x)O₃ (hereafter as PZT) piezoelectric ceramics. These single crystals have ultrahigh electromechanical coupling factor in the longitudinal mode (k₃₃>92%) and piezoelectric constant (d₃₃-2000pC/N), but lower dielectric loss tan8 is 1/3 of PZT-5H.Such excellent performances make single crystals promising candidates for medical imaging, especially in the developing harmonic imaging and multi-frequency imaging technique. It is critical to discover the outstanding properties of PMN-PT single crystals sufficiently and realize the application in the medical ultrasonic transducer based on grown successfully in batched with high quality, large size and consistent performances.In this dissertation, as grown (1-x) PMN-xPT single crystals were prepared with composition x is 0.30, 0.31 respectively, for a detail study. The investigation of elastic, dielectric piezoelectric, and acoustic performances in <001>-poled 0.70Pb (Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (0.70PMN-0.30PT) single crystals using a resonance technique were present, and the temperature stabilities also were analyzed. With poling the single crystals with rhombohedral symmetry along [001] of parent cubic axis, eight equivalent spontaneous polarization <111>_cub directions turn to four <11 l>_cub directions, which make them into desired multidomain structures with the effective tetragonal 4mm symmetry. The complete set of constants was determined for this <001>-poled domain engineered system by the 4mm symmetry. There are total of 11 independent physical constants describing the elasto-piezo-dielectric matrices for this symmetry.So there are six elastic constants( s_ij^E ,s_ij^D ,c_ij^D ,c_ij^D , ij=11, 12, 13, 33, 44, 66), three piezoelectric constants( e_mi , d_mi , g_mi , h_mi , mi = 15, 31, 33), and two dielectric...