Browsing by Author "Yang, Yaodong"
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- Anatomy of vertical heteroepitaxial interfaces reveals the memristive mechanism in Nb2O5-NaNbO3 thin filmsLi, Linglong; Lu, Lu; Wang, Zhiguang; Li, Yanxi; Yao, Yonggang; Zhang, Dawei; Yang, Guang; Yao, Jianjun; Viehland, Dwight D.; Yang, Yaodong (Springer Nature, 2015-03-18)Dynamic oxygen vacancies play a significant role in memristive switching materials and memristors can be realized via well controlled doping. Based on this idea we deposite Nb2O5-NaNbO3 nanocomposite thin films on SrRuO3-buffered LaAlO3 substrates. Through the spontaneous phase separation and self-assembly growth, two phases form clear vertical heteroepitaxial nanostructures. The interfaces between niobium oxide and sodium niobate full of ion vacancies form the conductive channels. Alternative I-V behavior attributed to dynamic ion migration reveals the memristive switching mechanism under the external bias. We believe that this phenomenon has a great potential in future device applications.
- Barium Titanate-Based Magnetoelectric NanocompositesYang, Yaodong (Virginia Tech, 2011-06-21)Barium Titanate (BaTiO3 or BTO) has attracted an ever increasing research interest because of its wide range of potential applications. Nano-sized or nanostructured BTO has found applications in new, useful smart devices, such as sensors and piezoelectric devices. Not only limited to one material, multi-layers or multi-phases can lead to multifunctional applications; for example, nanocomposites can be fabricated with ferrite or metal phase with BTO. In this study, I synthesized various BTO-ferrites, ranging from nanoparticles, nanowires to thin films. BTO-ferrite coaxial nanotubes, BTO-ferrite self-assemble thin films, and BTO single phase films were prepared by pulsed laser deposition (PLD) and sol-gel process. BTO-ferrite nanocomposites were grown by solid state reaction. Furthermore, BTO-metal nanostructures were also synthesized by solid state reaction under hydrogen gas which gave us a great inspiration to fabricate metal-ceramic composites. To understand the relationship between metal and BTO ceramic phase, I also deposited BTO film on Au buffered substrates. A metal layer can affect the grain size and orientation in BTO film which can further help us to control the distribution of dielectric properties of BTO films. After obtaining different nanomaterials, I am interested in the applications of these materials. Recently, many interesting electric devices are developed based on nanotechnology, e.g.: memristor. Memristor is a resistor with memory, which is very important in the computer memory. I believe these newly-synthesized BTO based nanostructures are useful for development of memristor, sensors and other devices to fit increasing needs.
- Controlled growth of epitaxial BiFeO3 films using self-assembled BiFeO3-CoFe2O4 multiferroic heterostructures as a templateLi, Yanxi; Yang, Yaodong; Yao, Jianjun; Viswan, Ravindranath; Wang, Z. G.; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2012-07-01)The growth mechanism of a BiFeO3 layer deposited on self assembled (0.65) BiFeO3-(0.35) CoFe2O4 (BFO-CFO) composite thin films was studied. Epitaxial and self-assembled BFO-CFO thin films were deposited on SrTiO3 (111) substrates by pulsed laser deposition and were subsequently used as a seed layer for the deposition of an additional BFO layer. x-ray line scans showed the heterostructures were highly epitaxial. Cross-sectional scanning electron microscopy and focused ion beam images revealed the top BFO layer grew preferentially from BFO nanopillars in the BFO-CFO thin films, thus, demonstrating controlled growth. The multiferroic properties of this new nanostructure were then studied. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4734508]
- Effect of Mn substituents on the domain and local structures of Na1/2Bi1/2TiO3-BaTiO3 single crystals near a morphotropic phase boundaryYao, Jianjun; Yang, Yaodong; Monsegue, Niven; Li, Yanxi; Li, Jiefang; Zhang, Qinhui; Ge, Wenwei; Luo, Haosu; Viehland, Dwight D. (AIP Publishing, 2011-03-01)The ferroelectric domain and local structures of Na1/2Bi1/2TiO3-x% BaTiO3 (NBT-BT) and 0.14 at. % Mn substituted Na1/2Bi1/2TiO3-x% BaTiO3 (Mn:NBT-BT) single crystals with x=5.5 near a morphotropic phase boundary have been investigated by transmission electron microscopy. Increased ferroelectric ordering and enhanced in-plane octahedral tilting were observed for Mn: NBT-BT compared with NBT-BT. Bragg-filtered lattice images revealed that the size of the in-phase tilt domains of Mn:NBT-BT were on the order of 2 to 8 nm, with a tendency of alignment along {110}. (C) 2011 American Institute of Physics. [doi:10.1063/1.3573801]
- Giant electric field controlled magnetic anisotropy in epitaxial BiFeO3-CoFe2O4 thin film heterostructures on single crystal Pb(Mg1/3Nb2/3)(0.7)Ti0.3O3 substrateWang, Zhiguang; Yang, Yaodong; Viswan, Ravindranath; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2011-07-01)We have deposited self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) thin films on Pb(Mg1/3Nb2/3)(0.7)Ti0.3O3 (PMN-PT) substrates and studied the change in magnetic anisotropy under different strain conditions induced by an applied electric field. After electric field poling, we observed (i) giant magnetization change: magnetization of original CFO phase is three times larger than that of strained one and (ii) magnetic force microscopy line profiles that exhibited significant change in the CFO magnetic domain response in accordance to magnetization-field (M-H) loops. Together, these results demonstrate good control of the magnetic properties of CFO via an electric field induced strain. (C) 2011 American Institute of Physics. [doi:10.1063/1.3619836]
- Magnetoelectric effect in crystallographically textured BaTiO3 films deposited on ferromagnetic metallic glass foilsWang, 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]
- Observation of partially incoherent <110> boundaries between polar nanodomains in Na1/2Bi1/2TiO3 single crystalsYao, Jianjun; Ge, Wenwei; Yang, Yaodong; Luo, Liang; Li, Jiefang; Viehland, Dwight D.; Bhattacharyya, Somnath; Zhang, Qinhui; Luo, Haosu (American Institute of Physics, 2010-09-15)The ferroelectric domain structure of Na1/2Bi1/2TiO3 single crystals was investigated by transmission electron microscopy (TEM) and piezoforce microscopy (PFM). Bright-field TEM and PFM images revealed the presence of polar nanodomains, whose boundaries had a tendency to align along the < 110 >. High resolution TEM images revealed planar defects along these < 110 > boundaries, which partially relaxed the coherency of the lattice. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488879]
- Pulsed Laser Deposition of BaTiO3 Thin Films on Different SubstratesYang, Yaodong; Wang, Zhiguang; Li, Jiefang; Viehland, Dwight D. (Hindawi Publishing Corporation, 2010)We have studied the deposition of BaTiO3 (BTO) thin films on various substrates. Three representative substrates were selected from different types of material systems: (i) SrTiO3 single crystals as a typical oxide, (ii) Si wafers as a semiconductor, and (iii) Ni foils as a magnetostrictive metal. We have compared the ferroelectric properties of BTO thin films obtained by pulsed laser deposition on these diverse substrates.