Crystal Growth And Property Characterization Of Lead-based Relaxor Ferroelectric Materials With High Phase Transition Temperature

Relaxor ferroelectric single crystal（1-x）Pb(Mg_1/3Nb_2/3)O₃-x Pb TiO₃ possesses excellent ferroelectric and piezoelectric properties,which makes it very useful in the application of underwater acoustic transducer,ultrasonic motor and pyroelectric devices.In recent years,the properties of PMN-PT crystal have been further optimized by doping or adding other components.In these methods,the addition of Pb Zr O₃ could be an effective way to make up the defects of existed materials.The reason is that the PMN-PT-PZ single crystal not only has higher phase transformation temperature,but also keeps the stability of excellent electrical properties.The advantage makes PMN-PT-PZ crystal become a material with high application value.In addition,the In doped PMN-PT crystal also has excellent electrical properties,and its growth of large size has been achieved successfully.Based on the above research,Pb(Mg_1/3Nb_2/3)O₃-Pb Ti O₃-Pb Zr O₃and Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-Pb TiO₃ crystals,which are abbreviated as PMN-PT-PZ and PIN-PMN-PT,were grown by vertical Bridgman method.And the characterization of PMN-PT-PZ crystal and the annealing effect on PIN-PMN-PT crystal were studied respectively.The Pb(Mg_1/3Nb_2/3)O₃-Pb Ti O₃-Pb Zr O₃crystalwiththestoichiometricratioof0.624/0.336/0.04 had been grown by the vertical Bridgman method.The size of the as-grown crystal is?25 mm×90 mm,whose polycrystalline materials were synthesized by the two-step solid-state reaction method at elevated temperature.The crystalline phase of as-grown crystal was characterized by the X-ray power diffraction（XRD）.The dielectric,ferroelectric and piezoelectric properties of crystal samples were also investigated.The results show that the as-grown crystal was in the pure perovskite structure,and its rhombohedral/tetragonal ferroelectric phase transition temperature T_rt was about 130℃ and Curie temperature T_c was between 165℃ and 170℃.The piezoelectric constant(d₃₃)of the wafers with（001）orientation taken from the rhombohedral crystal boule was in the range of 1300¹800 p C/N.The ferroelectric parameters of the crystal wafers were measured as a coercive field E_c of 4⁴.5 k V/cm and a remanent polarization P_rof20³1.5μC/cm2.Compared to PMN-PT single crystal,it is confirmed that PMN-PT-PZ single crystal possesses good electrical properties and a higher phase transformation temperature.According to the molar ratio of 0.3Pb(In_1/2Nb_1/2)O₃-0.4Pb(Mg_1/3Nb_2/3)O₃-0.3Pb Ti O₃,PIN-PMN-PT single crystal with size of?25 mm×100 mm had been grown from the stoichiometric melts by vertical Bridgman method.The pure perovskite structure of the as-grown crystal was characterized by X-ray power diffraction analysis（XRD）.A part of crystal samples were annealed,and after annealing,the color of samples became yellow.The dielectric,piezoelectric,ferroelectric and electromechanical coupling properties of annealed and unannealed wafers were characterized.The research results show that the unannealed crystal wafer had a Curie temperature T_c of 167^oC and the maximum dielectric permittivities was 60924.Its piezoelectric constant d₃₃ was more than 2000 p C/N and the ferroelectric parameters were measured as a coercive field E_c of 2.1³.2 k V/cm and a remanent polarization P_rof 25²7μC/cm2.While the annealed wafer had a Curie temperature T_c of 172℃ and the maximum of dielectric permittivities was 77610.Its piezoelectric constant d₃₃ was about 1783 p C/N and the ferroelectric parameters were measured as a coercive field E_c of 2.5³.6 k V/cm and a remanent polarization P_rof26.5²9.4μC/cm2.Compared the two results,it is confirmed that the properties of the annealed wafer are a little better than those of the unannealed one.