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Zhu, Yuanyuan

Publications and source records attributed to Zhu, Yuanyuan.

27 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Stabilizing new bismuth compounds in thin film form [Stabilizing new thin film materials in bismuth compounds]

Growth of unexpected phases from a composite target of BiFeO 3 :BiMnO 3 and/or BiFeO 3 :BiCrO 3 has been explored using pulsed laser deposition. The Bi 2 FeMnO 6 tetragonal phase can be grown directly on SrTiO 3 (STO) substrate, while two phases (S1 and S2) were found to grow on LaAlO 3 (LAO) substrates with narrow growth windows. However, introducing a thin CeO 2 buffer layer effectively broadens the growth window for the pure S1 phase, regardless of the substrate. Moreover, we discovered two new phases (X1 and X2) when growing on STO substrates using a BiFeO 3 :BiCrO 3 target. Pure X2 phase can be obtained on CeO 2 -buffered STO and LAO substrates. This work demonstrates that some unexpected phases can be stabilized in a thin film form by using composite perovskite BiRO 3 (R = Cr, Mn, Fe, Co, Ni) targets. Moreover, it also indicates that CeO 2 can serve as a general template for the growth of bismuth compounds with potential room-temperature multiferroicity.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Atomic-scale determination of active facets on the MoVTeNb oxide M1 phase and their intrinsic catalytic activity for ethane oxidative dehydrogenation

Atomic resolution aberration-corrected HAADF-STEM imaging has been used to directly image the basal (001) plane of the catalytically relevant M1 phase in MoVTeNb complex oxides. Facets {010}, {120} and {210} are identified as the most stable lateral terminations of the crystals. For each of these surface facets the average concentration of active sites is determined directly from the images. The most stable {010} facet does not expose active sites and is therefore regarded to be inactive. As a consequence, large flattened M1 particles are concluded to have a lower activity than other morphologies. This hypothesis is validated by a statistical analysis of two samples with rod vs. plate morphology. The concentration of sites and the catalytic activity in ethane oxidative dehydrogenation correlate perfectly, demonstrating quantitatively that the differences in reactivity between MoVTeNbOx catalysts of equal crystallinity and chemical composition depend primarily on the terminating facets that constitute the elongated catalyst particles.

MoVTeNbO, Oxidative Dehydrogenation, M1 phase, STE↗
DOE OSTI2016

Dose-rate controlled energy dispersive x-ray spectroscopic mapping of the metallic components in a biohybrid nanosystem

In this work, we showcase that through precise control of the electron dose rate, state-of-the-art large solid angle energy dispersive X-ray spectroscopy (EDS) mapping in aberration-corrected scanning transmission electron microscope (STEM) is capable of faithful and unambiguous chemical characterization of the Pt and Pd distribution in a peptide-mediated nanosystem. This low-dose-rate recording scheme adds another dimension of flexibility to the design of elemental mapping experiments, and holds significant potential for extending its application to a wide variety of beam sensitive hybrid nanostructures.

composition mapping↗
DOE OSTI2016

Two-Dimensional Layered Oxide Structures Tailored by Self-Assembled Layer Stacking via Interfacial Strain

Two-dimensional (2D) nanostructures emerge as one of leading topics in fundamental materials science and could enable next generation nanoelectronic devices. Beyond graphene and molybdenum disulphide, layered complex oxides are another large group of promising 2D candidates because of their strong interplay of intrinsic charge, spin, orbital and lattice. As a fundamental basis of heteroepitaxial thin film growth, interfacial strain can be used to design materials exhibiting new phenomena beyond their conventional form. Here we report the strain-driven self-assembly of Bismuth-based supercells (SC) with a 2D layered structure, and elucidate the fundamental growth mechanism with combined experimental tools and first-principles calculations. The study revealed that the new layered structures were formed by the strain-enabled self-assembled atomic layer stacking, i.e., alternative growth of Bi 2 O 2 layer and [Fe 0.5 Mn 0.5 ]O 6 layer. The strain-driven approach is further demonstrated in other SC candidate systems with promising room-temperature multiferroic properties. This well-integrated theoretical and experimental study inspired by the Materials Genome Initiatives opens up a new avenue in searching and designing novel 2D layered complex oxides with enormous promises.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Phase transition and critical behaviors of spin-orbital coupling spinel compound CdV{sub 2}O{sub 4}

The temperature dependent susceptibility and specific heat of spinel compound CdV{sub 2}O{sub 4} were investigated. The structural transition accompanied with orbital order appearing at 89.6 K is confirmed to be a first order transition, while the magnetic transitions at 30.2 K is revealed to be a second order one. For the paramagnetism-antiferromagnetic transition, the width of critical region was estimated to be about 1.5 K by differentiating with Gaussian fluctuation. In critical region, the critical behavior of specific heat was compared with renormalization-group theory. Critical exponent α and critical amplitude ratio (A{sup +}/A{sup −}) fitting to the data was found to be −0.017 and 1.26, respectively. The value of A{sup +}/A{sup −} shows the critical behavior of CdV{sub 2}O{sub 4}'s deviates from 3D-Heisenberg and shifts to 3D-XY. The analysis of specific heat in low temperature range gives out that Debye temperature Θ{sub D} for CdV{sub 2}O{sub 4} is estimated to be 190 K.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Location of Co and Ni promoter atoms in multi-layer MoS 2 nanocrystals for hydrotreating catalysis

The location of Co and Ni promoter atoms in industrial-style hydrotreating catalysts is examined by combining aberration-corrected scanning transmission electron microscopy and electron energy loss spectrum imaging. The observations unambiguously demonstrate that both Co and Ni promoter atoms occupy sites at all low-indexed edge terminations of hexagonally shaped multi-layer MoS 2 nanocrystals. In contrast, similar observations for single-layer MoS 2 nanocrystals show that Co-promoter atoms preferentially attach at the (-1 0 0) S-edge termination and are absent at the (1 0 0) Mo-edge termination. The apparent discrepancy between single- and multi-layer MoS 2 nanocrystals can be explained by the 2H-MoS 2 crystal structure, for which successive MoS 2 layers alternatingly expose Mo- and S-edge terminations in any of the low-indexed directions. Thus, the multi-layer Co-Mo-S and Ni-Mo-S nanocrystals, formed in the present type of industrial-style hydrotreating catalyst, are consistently described as a superposition of single-layer Co-Mo-S and Ni-Mo-S structures, and in turn, provide promoted edge sites with different steric accessibility for the organic compounds in mineral oil distillates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Research Updates: Epitaxial strain relaxation and associated interfacial reconstructions: The driving force for creating new structures with integrated functionality

Here, we report detailed strain mapping analysis at heterointerfaces of a new multiferroic complex oxide Bi{sub 3}Fe{sub 2}Mn{sub 2}O{sub x}(BFMO322) supercell and related layered structures. The state-of-the-art aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) and the modified geometric phase analysis (GPA) have been used to characterize the self-assembled transitional layers, misfit defects, and, in particular, the biaxial lattice strain distributions. We found that not only a sufficient lattice misfit is required through substrate selection and to be preserved in initial coherent epilayer growth, but also an appropriate interfacial reconstruction is crucial for triggering the growth of the new BFMO322 supercell structure. The observation of new transitional interfacial phases behaving like coherent film layers within the critical thickness challenges the conventional understanding in existing epitaxial growth model.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Oxygen-Vacancy-Induced Antiferromagnetism to Ferromagnetism Transformation in Eu 0.5 Ba 0.5 TiO 3–δ Multiferroic Thin Films

Oxygen vacancies (VO) effects on magnetic ordering in Eu 0.5 Ba 0.5 TiO 3–δ (EBTO 3–δ ) thin films have been investigated using a combination of experimental measurements and first-principles density-functional calculations. Two kinds of EBTO 3–δ thin films with different oxygen deficiency have been fabricated. A nuclear resonance backscattering spectrometry technique has been used to quantitatively measure contents of the V O . Eu 0.5 Ba 0.5 TiO 3 ceramics have been known to exhibit ferroelectric (FE) and G-type antiferromagnetic (AFM) properties. While, a ferromagnetic (FM) behavior with a Curie temperature of 1.85 K has been found in the EBTO 3–δ thin films. Spin-polarized Ti 3+ ions, which originated from the V O , has been proven to mediate a FM coupling between the local Eu 4ƒ spins and were believed to be responsible for the great change of the magnetic ordering. Considering the easy formation of V O , our work opens up a new avenue for achieving co-existence of FM and FE orders in oxide materials.

36 MATERIALS SCIENCE↗