Browsing by Author "Yan, Li"

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    Conformal sensor skin approach to the safety-monitoring of H-2 fuel tanks
    Dong, Shuxiang; Cao, Hu; Bai, Feiming; Yan, Li; Li, Jiefang; Viehland, Dwight D.; Gao, Y. K. (AIP Publishing, 2004-05-01)
    A conformal sensor skin approach has been developed for safety monitoring of H-2 fuel tanks. Small piezoelectrically driven sound resonance cavities were embedded in a porous polymer. When placed on a structural composite plate, it was found feasible to detect the leakage of small concentrations of H-2 in real time. (C) 2004 American Institute of Physics.
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    Deposition conditions and electrical properties of relaxor ferroelectric Pb(Fe1/2Nb1/2)O-3 thin films prepared by pulsed laser deposition
    Yan, Li; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2007-05-15)
    Epitaxial lead iron niobate thin films with thicknesses of 50 nm < t < 500 nm have been deposited by pulsed laser deposition. We have identified the deposition conditions that result in insulating layers. These critical conditions are essential to (i) prevent semiconducting resistivity characteristics, (ii) achieve higher induced polarizations of 70 mu C/cm(2) under E=190 kV/mm, and (iii) obtain remanent polarizations of 17.7 mu C/cm(2), coercive fields of 9.5 kV/mm, and dielectric constants of similar to 1200 at room temperature. (c) 2007 American Institute of Physics.
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    Direct measurement of magnetoelectric exchange in self-assembled epitaxial BiFeO3-CoFe2O4 nanocomposite thin films
    Yan, Li; Xing, Zengping; Wang, Z. G.; Wang, T.; Lei, G. Y.; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2009-05-01)
    We report the direct measurement of a magnetoelectric (ME) exchange between magnetostrictive CoFe2O4 nanopillars in a piezoelectric BiFeO3 matrix for single-layer nanocomposite epitaxial thin films grown on (001) SrTiO3 substrates with SrRuO3 bottom electrodes. The ME coefficient was measured by a magnetic cantilever method and had a maximum value of similar to 20 mV/cm Oe. The films possessed saturation polarization (60 mu C/cm(2)) and magnetization (410 emu/cc) properties equivalent to bulk values, with typical hysteresis loops.
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    Enhancement of multiferroic properties of Pb(Fe1/2Nb1/2)O-3 thin films on SrRuO3 buffered SrTiO3 substrates
    Yan, Li; Zhao, X.; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2009-05-01)
    We report multiferroic properties of Pb(Fe1/2Nb1/2)O-3 (or PFN) epitaxial thin layers grown on (001), (110), and (111) SrTiO3 substrates with and without a SrRuO3 (SRO) buffer. Our findings are as follows: (i) the constraint stress on (001) substrates is more than ten times larger than those on (110) and (111); (ii) this large constraint stress induces higher piezoelectric constants, magnetic permeability and magnetization for (001) PFN compared with (110) and (111) layers; (iii) epitaxy distorts the structure of (001) PFN causing the films to be weakly ferromagnetic, whereas (110) films are antiferromagnetic; and (iv) a significant increase of the coercivity of (001) layers occurs due to clamping by a SRO buffer layer.
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    Evolution of domain structures in Na1/2Bi1/2TiO3 single crystals with BaTiO3
    Yao, Jianjun; Yan, Li; Ge, Wenwei; Luo, L. A.; Li, Jiefang; Viehland, Dwight D.; Zhang, Qinhui; Luo, Haosu (American Physical Society, 2011-02-16)
    The domain structures of Na1/2Bi1/2TiO3-BaxTiO3 (NBT-x%BT) crystals for x = 0, 4.5, and 5.5 have been investigated by polarized light and piezoresponse force microscopies. The results show that BaTiO3 (i) refines the size of polar nanoregions and enhances their self-organization, and (ii) suppresses the formation of proper ferroelastic domains at high temperatures in the paraelectric state, and it rather favors the formation of improper ones that form below the ferroelectric Curie temperature and that elastically accommodate the ferroelectric ones.
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    The influence of Mn substitution on the local structure of Na0.5Bi0.5TiO3 crystals: Increased ferroelectric ordering and coexisting octahedral tilts
    Yao, Jianjun; Ge, Wenwei; Yan, Li; Reynolds, William T. Jr.; Li, Jiefang; Viehland, Dwight D.; Kiselev, Dmitry A.; Kholkin, Andrei L.; Zhang, Qinhui; Luo, Haosu (American Institute of Physics, 2012-03-15)
    The ferroelectric domain structure of pure Na1/2Bi1/2TiO3 (NBT) and 1 at.% Mn-doped NBT (Mn-NBT) crystals was investigated by piezoresponse force microscopy. The correlation length of the polar regions was found to increase upon Mn substitution. High resolution transmission electron microscopy revealed that the coherency of the lattice across the domain boundaries between polar regions was also enhanced. Selected area electron diffraction showed that Mn favored coexisting 1/2 (ooo) and 1/2 (ooe) oxygen octahedral tiltings, over only 1/2 (ooo) for pure NBT. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3699010]
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    Low symmetry phase in Pb(Zr0.52Ti0.48)O-3 epitaxial thin films with enhanced ferroelectric properties
    Yan, Li; Li, Jiefang; Cao, Hu; Viehland, Dwight D. (AIP Publishing, 2006-12-01)
    The authors report the structural and ferroelectric properties of Pb(Zr0.52Ti0.48)O-3 (PZT) epitaxial thin films grown on (001), (110), and (111) SrRuO3/SrTiO3 substrates by pulsed laser deposition. A monoclinic C (M-c) phase has been found for (101) films, whereas (001) and (111) ones were tetragonal (T) and rhombohedral (R), respectively. The authors find that the ferroelectric polarization of the M-c phase is higher than that in either the T or R ones. These results are consistent with predictions (i) of epitaxial phase diagrams and (ii) that the enhanced ferroelectric properties of morphotropic phase boundary PZT are related to a low symmetry monoclinic phase. (c) 2006 American Institute of Physics.
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    Magnetoelectric and multiferroic properties of variously oriented epitaxial BiFeO3-CoFe2O4 nanostructured thin films
    Yan, Li; Wang, Zhiguang; Xing, Zengping; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2010-03-15)
    We report the ferroelectric, ferromagnetic, and magnetoelectric (ME) properties of self-assembled epitaxial BiFeO3-CoFe2O4 (BFO-CFO) nanostructure composite thin films deposited on (001), (110), and (111) SrTiO3 (STO) single crystal substrates. These various properties are shown to depend on orientation. The maximum values of the relative dielectric constant, saturation polarization, longitudinal piezoelectric coefficient, saturation magnetization, and ME coefficient at room temperature were 143, 86 mu m/cm(2), 50 pm/V, 400 emu/cc, and 20 mV/cm Oe, respectively.
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    Magnetoelectric effect in crystallographically textured BaTiO3 films deposited on ferromagnetic metallic glass foils
    Wang, Zhiguang; Yan, Li; Yang, Yaodong; Li, Jiefang; Das, Jaydip; Geiler, Anton L.; Yang, Aria F.; Chen, Yajie; Harris, Vincent G.; Viehland, Dwight D. (American Institute of Physics, 2011-02-01)
    We demonstrate a significant control of the polarization response under an applied magnetic field for a magnetoelectric (ME) heterostructure. This structure was comprised of a 2 mu m thick ferroelectric BaTiO3 (BTO) film deposited on flexible ferromagnetic metallic glass foil (25 mu m thick). Au was used as a buffer layer to control BTO growth orientation, and to protect the metallic glass from oxidation. x-ray diffraction and scanning electron microscopy demonstrated the successful growth of well-crystallized BTO films with a high degree of (111) orientation on the amorphous metallic glass foils. Well-defined polarization (P-E) and magnetization (M-H) hysteresis loops confirmed the coexistence of ferroelectric and ferromagnetic properties. A ME voltage coefficient of about similar to 60 mV/cm Oe was measured. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3544352]
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    Magnetoelectric properties of flexible BiFeO3/Ni tapes
    Yan, Li; Zhuo, M.; Wang, Z.; Yao, J.; Haberkorn, N.; Zhang, S.; Civale, L.; Li, J.; Viehland, Dwight D.; Jia, Q. X. (AIP Publishing, 2012-07-01)
    We report ferroelectric (FE), ferromagnetic, and magnetoelectric (ME) properties of BiFeO3 films directly deposited on flexible magnetic Ni tapes. Without use of metal-oxide and/or noble metal buffer layer between the BiFeO3 and the Ni, both ferroelectric and magnetic properties of the film and the substrate are preserved. X-ray diffraction and transmission electron microscopy analyses confirm the formation of preferentially oriented (110) BiFeO3 film on Ni tapes. The BiFeO3 film has a saturation polarization and a piezoelectric d(33) coefficient of 69 mu C/cm(2) and 52 pm/V, respectively. The BiFeO3/Ni tape shows a magnetoelectric coefficient of 3.5 mV/cm.Oe. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731780]
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    Multiferroic epitaxial Pb(Fe1/2Nb1/2)O-3 thin films: A relaxor ferroelectric/weak ferromagnet with a variable structure
    Yan, Li; Li, Jiefang; Suchicital, Carlos T. A.; Viehland, Dwight D. (AIP Publishing, 2006-09-01)
    The authors report the structural, ferroelectric, and ferromagnetic properties of Pb(Fe1/2Nb1/2)O-3 epitaxial thin layers grown on (001), (110), and (111) SrTiO3 substrates by pulsed-laser deposition; films were of sufficient resistivity to enable high-field P-E measurements. Findings are as follows: epitaxial strain results in (i) a dramatic increase in the spontaneous polarization P-s; (ii) a lattice structure that is dependent on substrate orientation; (iii) a slim-loop P-E response and relaxor ferroelectric characteristics in the dielectric constant, both of which are nearly independent of crystallographic orientation; and (iv) a weak ferromagnetic moment, which is dependent on epitaxial mismatch. (c) 2006 American Institute of Physics.
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    Nanogrowth twins and abnormal magnetic behavior in CoFe2O4 epitaxial thin films
    Yan, Li; Wang, Yu; Li, Jiefang; Pyatakov, Alexander P.; Viehland, Dwight D. (American Institute of Physics, 2008-12-15)
    Nanogrowth twins (GTs) have been observed in CoFe2O4 (CFO) epitaxial thin films deposited on (111) oriented SrTiO3 substrates by pulsed laser deposition. The GTs form during nucleation and growth and consist of CFO growth regions that have a mirror relationship with respect to each other. We show that the films with GTs (i) are better crystallized than the ones without them and (ii) have higher saturation magnetizations due to the presence of twin boundaries.
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    A piezoelectric single crystal traveling wave step motor for low-temperature application
    Dong, Shuxiang; Yan, Li; Viehland, Dwight D.; Jiang, X. N.; Hackenberger, Wesley S. (AIP Publishing, 2008-04-01)
    A piezoelectric Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) single crystal traveling wave rotary motor operated in a stepping motion for cryogenic actuations was developed and characterized. This single crystal stepping motor had a torque of >= 1.5 kg cm, an excess of 1800 steps per revolution about its axis, and a power consumption of <= 2 W by using a step motion with 25% duty cycle. We then show that this single crystal motor can successfully operate at 77 K (liquid nitrogen) under a load. (c) 2008 American Institute of Physics. (c) 2008 American Institute of Physics.
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    Resonant bending mode of Terfenol-D/steel/Pb(Zr,Ti)O-3 magnetoelectric laminate composites
    Xing, Zengping; Dong, Shuxiang; Zhai, Junyi; Yan, Li; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2006-09-01)
    Resonant bending-mode Tb1-xDyxFe2-y/elastic-steel/Pb(Zr,Ti)O-3 magnetoelectric (ME) laminate composites have been investigated. An elastic-steel layer with a relatively high Q(m) significantly increases the resonant enhancement of the ME coefficient due to an increased effective Q(m) of the laminate. The three-phase ME laminates have a low first-order bending frequency of similar to 5 kHz, with a resonance-enhanced ME coefficient of similar to 40 V/cm Oe. (c) 2006 American Institute of Physics. (c) 2006 American Institute of Physics.
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    A small, linear, piezoelectric ultrasonic cryomotor
    Dong, Shuxiang; Yan, Li; Wang, Naigang; Viehland, Dwight D.; Jiang, Xiaoning; Rehrig, P.; Hackenberger, Wesley S. (AIP Publishing, 2005-01-01)
    A small, linear-type, piezoelectric ultrasonic cryomotor has been developed for precision positioning at extremely low temperatures (greater than or equal to-200 degreesC). This cryornotor consists of a pair of Pb(Mgl(1/3)Nb(2/3))O-3-PbTiO3 single crystal stacks, which are piezoelectrically excited into the rotating third-bending mode of the cryomotor stator's center, which in turn drives a contacted slider into linear motion via frictional forces. The performance characteristics achieved by the cryornotor are: (i) a maximum linear speed of >50 mm/s; (ii) a stroke of >10 mm; (iii) a driving force of >0.2 N; (iv) a response time of similar to29 ms; and (v) a step resolution of similar to20 nm. (C) 2005 American Institute of Physics.
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    Structure of (001)-, (110)-, and (111)-oriented Pb(Fe1/2Nb1/2)O-3 epitaxial thin films on SrRuO3-buffered SrTiO3 substrates
    Yan, Li; Li, Jiefang; Viehland, Dwight D. (Cambridge University Press, 2008-03-01)
    We have studied the lattice structure of variously oriented lead iron niobate (PFN) thin films with thicknesses of 50 < t < 500 nm that were deposited by pulsed laser deposition (PLD). We have identified that (001)-, (110)-, and (111)-oriented PFN thin films have tetragonal, orthorhombic, and rhombohedral phases at room temperature, respectively. The change in phase stability, when deposited on substrates of different orientations, is discussed with respect to the influence of epitaxial stress.
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    Triclinic phase in tilted (001) oriented BiFeO3 epitaxial thin films
    Yan, Li; Cao, Hu; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2009-03-01)
    We report a triclinic phase in perovskite BiFeO3 (BFO) epitaxial thin films grown on (130) and (120) oriented SrTiO3 substrates. The lattice constants of the BFO thin films changed with tilt of the substrates from (001) toward (110). These lattice parameters result from the epitaxially engineering of structurally bridging phases of the lowest possible symmetry.
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    Two phase magnetoelectric epitaxial composite thin films
    Yan, Li (Virginia Tech, 2009-11-03)
    Magnetoelectricity (ME) is a physical property that results from an exchange between polar (electric dipole) and spin (magnetic dipole) subsystem: i.e., a change in polarization (P) with application of magnetic field (H), or a change in magnetization (M) with applied electric field (E). Magnetoelectricity can be found both in single phase and composite materials. Compared with single phase multiferroic materials, composite multiferroics have higher ME effects. Through a strictive interaction between the piezoelectricity of the ferroelectric phase and the magnetostriction of the ferromagnetic phase, said multiferroic composites are capable of producing relatively large ME coefficients. This Dissertation focused on the deposition and characterization of two-phase composite magnetoelectric thin films. First, single phase ferroelectric thin films were studied to improve the multiferroic properties of the composite thin films. Then structural, ferroelectric, ferromagnetic, and magnetoelectric properties of composite thin films were researched. Finally, regular nano-array composite films were deposited and characterized. First, for single phase ferroelectric thin films, the phase stability was controlled by epitaxial engineering. Because ferroelectric properties are strongly related to their crystal structure, it is necessary to study the crystal structures in single phase ferroelectric thin films. Through constraint of the substrates, the phase stability of the ferroelectric thin films were able to be altered. Epitaxial thin-layers of Pb(Fe1/2Nb1/2)O3 (or PFN) grown on (001), (110), and (111) SrTiO3 substrates are tetragonal, orthorhombic, and rhombohedral respectively. The larger constraint stress induces higher piezoelectric constants in tetragonal PFN thin film. Epitaxial thin-layers of Pb(Zr0.52Ti0.48)O3 (or PZT) grown on (001), (110), and (111) SrTiO3 substrates are tetragonal, monoclinic C, and rhombohedral respectively. Enhanced ferroelectric properties were found in the low symmetry monoclinic phase. A triclinic phase in BFO was observed when it was deposited on tilted (001) STO substrates by selecting low symmetry (or interim) orientations of single crystal substrates. Then, in two phase composite magnetoelectric thin films, the morphology stability was controlled by epitaxial engineering. Because multiferroic properties are strongly related to the nano-structures of the composite thin films, it is necessary to research the nano-structures in composite thin films. Nano-belt structures were observed in both BaTiO3-CoFe2O4 and BiFeO3-CoFe2O4 systems: by changing the orientation of substrates or annealing condition, the nano-pillar structure could be changed into nano-belts structure. By doing so, the anisotropy of ferromagnetic properties changes accordingly. The multi-ferroic properties and magnetoelectric properties or (001), (110) and (111) self-assembled BiFeO3-CoFe2O4 nano-composite thin film were also measured. Finally, the regular CoFe2O4-BiFeO3 nano-array composite was deposited by pulsed laser deposition patterned using a focused ion beam. Top and cross-section views of the composite thin film showed an ordered CoFe2O4 nano-array embedded in a BiFeO3 matrix. Multiferroic and magnetoelectric properties were measured by piezoresponse force microscopy and magnetic force microscopy. Results show (i) switching of the magnetization in ferromagnetic CoFe2O4 and of the polarization in ferroelectric BiFeO3 phases under external magnetic and electric field respectively, and (ii) changes of the magnetization of CoFe2O4 by applying an electric field to the BiFeO3 phase.
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    Vacuum response and gas leak detection in piezoelectrically driven sound-resonance cavity
    Dong, Shuxiang; Bai, Feiming; Yan, Li; Cao, Hu; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2004-05-01)
    It has been found that a piezoelectrically driven sound-resonance cavity (PSRC) is quite sensitive to low-pressure changes: a change from ambient to vacuum (67 Pa) conditions results in a 89degrees phase shift and a -81% voltage decrease. Under vacuum conditions, the PSRC is highly sensitive (similar to7 ppm) to leakage of H-2 gas. (C) 2004 American Institute of Physics.