Study On The Structure And Electrical Properties Of The High Curie Point Relaxor Ferroelectric PIMNT

Relaxor ferroelectric materials of lead magnesium niobate-lead titanate system have excellent ferroelectric properties,dielectric properties,piezoelectric properties and pyroelectric properties,which have important application prospects in the fields of microelectronics,integrated ferroelectrics,microelectromechanical systems.Considering the low Curie point and phase transition temperature of binary lead magnesium niobate-lead titanate single crystal during application,the high Curie point relaxation ferroelectric system,represented by the new generation of Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃?PIMNT?represents,has attracted wide attention.It is expected that while maintaining the excellent electrical performance of the binary system,the operation temperature range of the device can be greatly broadened.This thesis focused on the structure and electrical properties of high Curie point relaxor ferroelectric materials of PIMNT system.The main research contents and results are as follows:1.The domain structure,ferroelectric properties,piezoelectric properties and dielectricpropertiesof0.3Pb(In_1/2Nb_1/2)O₃-0.4Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃?PIMNT?30/40/30??single crystal at normal temperature and variable temperature were studied.At 1 kHz,the dielectric constant?_r and loss tan?of the single crystal were 4046 and 0.008 respectively.Frequency constant N_t,electromechanical coupling coefficient k_t and quality factor Q_m were 1896 kHz·mm,0.56 and 120respectively.Piezoelectric coefficient(9^*₃₃ was 1034 pm/V.Residual polarization intensity P_r and coercive field E_c were 23?C/cm² and 2.9 kV/cm respectively.At room temperature,the domain size was 100-300 nm.The polar micro region and typical piezoelectric hysteresis loop can be observed.The study of domain structure at different temperatures indicated that the domain structure of PIMNT single crystal could persist up to 180?C,which was substantially higher than the Curie temperature.Moreover,the weak butterfly shape piezoelectric response at 180?C could be substantially enhanced with the local DC field increasing to 25 V.The corresponding physical mechanism was analyzed and discussed.2.PIMNT films were grown on SrRuO3?SRO?buffered SrTiO3?STO?single-crystal substrate by pulsed laser deposition?PLD?.The effect of oxygen partial pressure on the structure and electrical properties of PIMNT thin film were studied.Under the conditions of 600?C and 20 Pa,the relative dielectric constant of 1 kHz is as high as2234 at room temperature.Coercive field E_c and residual polarization intensity P_r were5.6 kV/mm and 40?C/cm² respectively.3.The effect of substrate temperature on the piezoelectric,dielectric,ferroelectric properties of PIMNT thin films and their physical mechanism were further studied.The PIMNT films were prepared at the substrate temperature of 550?C to 620?C.Pure perovskite structures can be obtained for all the substrate temperatures with no obvious peak splitting or shifting.Dense microstructure could be observed from the SEM surface and cross-sectional results,which indicated that the films were well-crystallized.The remnant polarization intensity P_r located between 23.9?C/cm² and 45.2?C/cm²and the relative dielectric constant?_r varied from 1257 to 1563.These indicated the dielectric constants of PIMNT films exhibited weak temperature dependence during the studied temperature range.Under the conditions of 620?C and 15 Pa,the thickness of the film was 315 nm.The piezoelectric coefficient was 40 pm/V.The leakage current response was dominated by ohmic conduction mechanism and FN tunneling effect in weak field and strong field,respectively.PFM results indicated that the thin film under this condition has obvious ferroelectric domain structure and local piezoelectric response.