H. S. Luo

Dielectric properties of 65PMN-35PT/P(VDF-TrFE) 0-3 composites

Lead magnesium niobate-lead titanate (PMN-PT with 35 mol.% PT) single crystal powder has been incorporated into a polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE) 70/30 mol.%) copolymer matrix to form 0-3 composites. With 65/35 mol.% composition, PMN-PT has high piezoelectric properties as a result of the enhanced polarizability arising from the coupling between two equivalent energy states. P(VDF-TrFE) ferroelectric copolymer films can be poled to give piezoelectric and pyroelectric performance without prior mechanical stretching. The composites were prepared using solvent casting to disperse the single crystal powder homogeneously in the matrix. Composites with PMN-PT volume fraction φ ranging from 0.05 to 0.4 were fabricated using a hot-press method. The relative permittivity and pyroelectric coefficients of the composites were measured as a function of φ. Good agreement has been obtained between the theoretical and experimental values. Under the same poling condition, the composites have higher pyroelectric coefficient than the pure copolymer films. Hysteresis measurements reveal that the remanent polarization of composites increases as φ increases.

Domain structure of adaptive orthorhombic phase in [110]-poled Pb(Mg1∕3Nb2∕3)O3–30.5%PbTiO3 single crystal

The domain structure of orthorhombic phase in [110]-poled Pb(Mg1∕3Nb2∕3)O3–30.5%PbTiO3 has been studied with analytical transmission electron microscopy. Convergent beam electron diffraction analysis indicates that the orthorhombic phase is an adaptive phase composed of tetragonal nanodomains while in the macroscopic scale it appear as orthorhombic due to an average effect. When poled along [110] direction, the volume ratio of the nanodomains with [100] polarization becomes equal to that of the nanodomains with [010] polarization. The nanodomain walls seem pinned, which may be a reason of the lower piezoelectric properties of orthorhombic phase.

Polarized micro-Raman study of the field-induced phase transition in the relaxor 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 single crystal

Polarized Raman spectroscopy has been performed to investigate the effects of the electric field on 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 (PMN–33%PT) single crystal. The electric-field-evolution of Raman spectra differed from one microarea to another. In the crossed polarization geometry, the abrupt changes in the intensities of the Raman bands at around 570 and 780 cm−1 indicated the occurrence of the field induced phase transition from the MC-type to the MA-type monoclinic structure. On the other hand, the Raman spectra for the microarea that was initially in the MA phase exhibited no obvious changes. All these results revealed the microheterogeneity in PMN–33%PT single crystal, which is useful for understanding the field-induced superior electromechanical properties.

Substrate-induced strain effect in La0.875Ba0.125MnO3 thin films grown on ferroelectric single-crystal substrates

The authors have studied the substrate-induced strain effect in La0.875Ba0.125MnO3 (LBMO) thin films grown on ferroelectric 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 (PMN-PT) single-crystal substrates. Both the strain and resistance of the films can be in situ varied by applying an electric field across the PMN-PT substrates. X-ray diffraction analysis indicates that the variations of strain and resistance result from the induced strain in the PMN-PT substrate due to the ferroelectric polarization or the converse piezoelectric effect. The relationships between the resistance and the induced strain in the LBMO film and PMN-PT substrate have been quantitatively analyzed.

Strain-mediated electric-field control of resistance in the La0.85Sr0.15MnO3∕0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 structure

The authors have deposited thin films of La0.85Sr0.15MnO3 (LSMO) on 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 (PMN-PT) single-crystal substrates and have achieved modulation of the resistance of the LSMO film by applying an electric field across the PMN-PT substrate whether the LSMO film is in the paramagnetic, ferromagnetic, or charge-ordered state. Piezoelectric measurements show that the electric field gives rise to a lattice strain in the PMN-PT substrate via the converse piezoelectric effect, which then induces a lattice strain and hence a resistance change in the LSMO film. Analysis of the data indicates that the electric-field-induced lattice strain effect dominates over the field effect in the LSMO/PMN-PT structure.

Investigation of substrate-induced strain effects in La0.7Ca0.15Sr0.15MnO3 thin films using ferroelectric polarization and the converse piezoelectric effect

We have fabricated manganite film/ferroelectric crystal heterostructures by growing La0.7Ca0.15Sr0.15MnO3 (LCSMO) films on ferroelectric 0.67Pb(Mg1/3Nb2/3)O3−0.33PbTiO3 (PMN-PT) single-crystal substrates. The efficient mechanical coupling at the interface, originated from ferroelectric polarization or the converse piezoelectric effect in the PMN-PT substrate, gives rise to large changes in the strain state, electrical resistance, magnetoresistance, and insulator-to-metal transition temperature (TP) of the film. We interpreted all these changes in terms of substrate-induced strain, which modifies the tetragonal distortion of MnO6 octahedra and the electron-lattice coupling strength in the film. Quantitative relationships between TP and induced strain in the LCSMO film have been established.

Ultrahigh piezoelectric response perpendicular to special cleavage plane in BaTiO3 single crystals

We report on the ultrahigh piezoelectric response perpendicular to some special cleavage plane in BaTiO3 single crystals. An extremely high value of piezoelectric coefficient d33 value over 2000pC∕N was obtained after being poled perpendicular to special plane (270) in BaTiO3 crystal, which is more than 20 times higher than those poled along spontaneous polarization direction ⟨001⟩ (d33⟨001⟩=87pC∕N). A large strain of 0.6% was obtained at a very low electric field.

High frequency PMN–PT single crystal focusing transducer fabricated by a mechanical dimpling technique

High frequency (∼30MHz and ∼80MHz) focusing ultrasound transducers were fabricated using a PMN-0.28PT single crystal by a mechanical dimpling technique. The dimpled single crystal was used as an active element for the focusing transducer. Compared with a plane transducer, the focusing transducer fabricated with a dimpled active element exhibits much broader bandwidth and higher sensitivity. Besides, a high quality image can be obtained by the 30MHz focusing transducer, in which the -6dB axial and lateral resolution is 27μm and 139μm, respectively. These results prove that the dimpling technique is capable to fabricate the high frequency focusing transducers with excellent performance for imaging applications.

Time- and temperature-dependent domain evolutions in poled (111)-cut (Pb(Mg1∕3Nb2∕3)O3)0.7(PbTiO3)0.3 single crystal

Ferroelectric domain evolution in poled (111)-cut (Pb(Mg1∕3Nb2∕3)O3)0.7(PbTiO3)0.3 single crystal has been studied by means of piezoresponse force microscopy (PFM). A time-dependent development of lamellar ferroelectric domains from a single domain structure of the just-poled sample has been observed, and it reveals that the formation of the lamellar macrodomains is via the accumulation of well-aligned speckle-shaped nanodomains grown from polar nanosized regions (PNRs). The domain evolutions from macrodomain to microdomain, and from ferroelectric to paraelectric phase at different temperatures, have been revealed in temperature-dependent PFM imaging, and the results are consistent with temperature-dependent relative permittivity measurement. PNRs are believed to play a key role in the domain evolution of depolarization process.

Large and electric field tunable superelasticity in BaTiO3 crystals predicted by an incremental domain switching criterion

Superelasticity is very common in shape memory alloys but is rather difficult to realize in ferroelectric ceramics and had never appeared in normal ferroelectric single crystals. Here we show that guided by a proposed incremental 90° domain switching criterion, large and electric-field-tunable superelastic strains up to 0.85% has been realized in a specially poled BaTiO3 crystal cube via compression loading/unloading with a positive dc bias electric field along the poling direction. Moreover, the tunable superelasticity has a large damping factor of up to 0.76, which is very promising in intelligent damping devices.