| Antiferroelectric (AFE) crystals are promising candidates for dielectrics in high energy density electrical capacitors especially for large size capacitor devices due to the reversible electric field-induced antiferroelectric-ferroelectric phase transition. Piezo/ferro-electric crystal is widely used for the production of piezoelectric transducers, detectors, memorys and other components. For some demanding applications, it is required to have excellent physical properties such as high dielectric constant, high pizeoelectrical activity, high electromechanical coupling coefficient, high mechanical quality factor, low loss and so on. The characteristics of lead based perovskites materials with lutetium show high Curie temperature and possible good performance, which are worth being studied.A Pb(Lu1/2Nb1/2)O3 (PLN) antiferroelectric crystal with tetrakaidecahedron combination in habit and orthorhombic in nature is successfully obtained for the first time by a high-temperature solution technique. Two sets of superlattice reflections including the B-site atom ordering type reflection and the antiparallel lead-atom ordering type reflection are confirmed and distinguished by the X-ray diffraction patterns (XRD) and transmission electron microscope (TEM). The Curie temperature Tc is measured to be near 240 "C with a low dielectric constant (?102). The double hysteresis loops of PLN crystal platelets are displayed with an electric field EAPP = 170 kV/cm applied. The value of energy density is calculated to be 3.65 J/cm3 at 200 ?. All the above features, especially the high Curie temperature and high energy storage capabilities, suggest that the PLN single crystals should be useful for large size capacitor devices or explosion energy conversion device that require a wide operation temperature range.Series of La-modified PLN (LaxPb1-3x/2(Lu1/2Nb1/2)O3, x = 0.01,0.03,0.05) and Na-La-modified PLN ((NaxLaxPb1-2x)(Lu1/2Nb1/2)O3, x = 0.06) AFE crystals are successfully obtained by a high-temperature solution technique. The structural phase transitions and the electrical behavior have been investigated. XRD and Atomic Emission Spectrometry (ICP) analysis indicates that La3+ and Na+ have diffused into the lattices and the crystals display pure perovskite structures. It is found that Curie temperature 7c for AFE transition decreases from 224 ? to 162 ? with the increasing La3+ content, while increase upon Na+ content modified. Compared to PLN antiferroelectric crystals, the energy storage performance was greatly enhanced, such as 1%La-PLN, the unsaturated value of energy storage density is calculated up to 4.5 J/cm3 at 200 ?.AFE crystals Pb(Lui1/2Nb1/2)O3-xPbTiO3 (x = 0.051,0.075) are successfully obtained by a top-seed solution growth (TSSG) technique. The polarization-electric field (P-E) hysteresis loops of PLN-0.075PT crystal at various temperatures suggest that the crystal transformed from ferroelectric phase to antiferroelectric phase then to paraferroelectric phase with the temperature increasing. A small amount of PT-doped AFE PLN-PT crystals show low open field and good energy storage density, such as PLN-0.075PT crystal, the value of energy storage density is calculated up to 3.0 J/cm3 at 160 ?, which provides a base for the modified and appilied extension of PLN crystals.A series of new (1-x)Pb(Lui/2Nbi/2)O3-xPbTi03 (PLN-xPT, x = 0.205,0.221,0.235, 0.281,0.328,0.423,0.446,0.474,0.489,0.513,0.521,0.554,0.566,0.628) binary ferroelectric crystals with high Curie temperature have been successfully obtained by TSSG method. The XRD and polarized light microscope (PLM) analyses confirm the coexistence of rhombohedral and tetragonal phase within the Morphotropic phase boundary (MPB). Furthermore, those compositions within MPB exhibit good comprehensive piezoelectric properties. For example, the crystal PLN-0.49PT, showing high Curie temperature Tc of about 360 ? and high rhombohedral-tetragonal phase transition temperature TRT of about 110 ?. And the piezoelectric coefficient d.33, electromechanical coupling coefficient k33, coercive field Ec and remanent polarization P, are found to be 1630 pC/N,81%,13.8 kV/cm and 26.6 ?C/cm, respectively. The large coercive field and high Tc make it a promising candidate for high power transducers in a wide temperature range.According to previous work on antifeirroelectric PLN-PT and ferroelectric PLN-PT, a solid state phase diagram in the low temperature range has been established, which reveals a morphotropic phase boundary (MPB) in the range of 49%-51% PT. This suggest that the phase structure of PLN-xPT at room temperature changes from Orthorhombic (space group Bmm2) to rhombohedral (space group R3m) to tetragonal (space group P4mm) with the increasing x. From another point of view, the crystals changes from antiferroelectrics to relaxor ferroelectrics then to normal ferroelectrics with the increasing x.Ferroelectric crystals of Pb(Lui/2Nb1/2)O3-Pb(Mg1/3Nb23)O3-PbTiO3 ternary solid solution system with high Curie temperature, in the vicinity of morphotropic phase boundary (MPB) region, are grown by TSSG method. The compositions and structures of the crystals are analyzed. All diffraction patterns present pure perovskite structure. The di-/piezo-/ferro-electric properties of the crystals are also characterized systematically. The Curie temperature Tc and coercive field Ec, increase gradually with increasing PT content. In particular,0.34PLN-0.31PMN-0.35PT crystal exhibits excellent electric properties including the Curie temperature, the rhombohedral-tetragonal phase transition temperature, the piezoelectric coefficient, the remnant polarization and the coercive field, which are 228 ?,156 ?,2092 pC/N,35.5?C/cm and 8.1 kV/cm, respectively, making 0.34PLN-0.31PMN-0.35PT crystal a promising material for transducers and detectors in a wide temperature range. |
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