Two-Dimensional Bismuth-Based Layered Supercell for Multiferroism

Room-temperature multiferroics, possessing ferroelectricity and ferromagnetism simultaneously in one phase, hold great promise in miniaturized devices including sensors, actuators, transducers, and multi-state memories. However, single-phase multiferroics are scarce because of the drastically different orbital requirements for ferroelectricity (requiring empty d-orbital) and ferromagnetism (coming from partially filled d-orbitals). Combining two cations possessing ferroelectric and ferromagnetic ordering respectively into one phase is one of the effective routes towards creating single-phase multiferroic materials, such as the Bi-based perovskites BiFeO3 and Bi2FeMnO6. For Bi-based perovskites, the ferroelectricity comes from the high stereochemical activity of the lone-pair electrons of the Bi^3+ cation and the B-site cation provides the magnetism. Bi3Fe2Mn2O10+δ supercell (BFMO322 SC) is a layered structure with enhanced ferroelectricity and magnetism compared to the conventional pseudocubic Bi2FeMnO6 phase. BFMO322 SC has been fabricated on LaAlO3 (001) substrate and can also be fabricated on CeO2 buffer layer. In this dissertation, the influence of CeO2 thickness to the growth and magnetic property of BFMO322 SC has been first investigated. The result shows that a CeO2 buffer layer as thin as 6.7 nm is sufficient to trigger the growth of BFMO322 SC and the sample exhibits the best magnetic properties with both highest magnetization and anisotropy. The growth of BFMO322 SC with high phase purity and superior magnetic properties on CeO2 with a thickness of 6.7 nm is attributed to the lattice match between Ce-Ce and Bi-Bi bond as well as the smooth surface of CeO2 buffer layer. Next, the influence of Fe/Mn molar ratio to the growth and magnetic property of Bi-based layered supercell structure has been studied by both experimental and theoretical methods. It was found that that Mn is more important than Fe in facilitating the growth of Bi-based layered supercell structures. With more Fe than Mn in the structure, the layered supercell structure cannot be formed. The three-dimensional distribution of Young’s modulus of the Bi-based layered supercell structures is calculated based on density functional theory. The theoretical calculation indicates that the strain energy is too high to keep the layered supercell structure if there is more Fe than Mn. In particular, the layered supercell structure with Bi2Ox slabs can also be obtained on CeO2 buffer layer and SrTiO3 (001) for single-perovskite BiMnO3 under well controlled growth conditions. Then tunable layered supercell (SC) structures have been designed and achieved in both BiMnO3 and Bi2NiMnO6 thin films. More specifically, both supercells with two layer BiOx-slabs (2-Bi SC) and three layer structure BiOx-slabs (3-Bi SC) have been achieved on both LaAlO3 (001) and SrTiO3 (001) under deposition parameter tuning. The novel layered supercell structures consist of alternative layered stacking of Bi2Ox (or Bi3Ox) slabs and Mn-O (or Ni-Mn-O) octahedra layers along out-of-plane direction, respectively. Both the BiMnO3 and Bi2NiMnO6 layered supercell structures exhibit robust multiferroic response at room temperature and tunable ferromagnetic and optical properties attributed to the variable SC structures. Finally, a new layered supercell structure with Bi3Ox slabs has been designed and fabricated from the new material system Bi2AlMnO6 (BAMO). The new BAMO layered supercell structure is self-assembly grown by alternative layered stacking of three-layer-thick Bi-based slabs [Bi3O3+δ] and one-layer-thick [MO2]∞ layer (M = Al/Mn). It can be fabricated on single-crystal substrates SrTiO3 (001) and LaAlO3 (001), with or without CeO2 (001) and La0.7Sr0.3MnO3 (001) buffer layers. Robust room-temperature multiferroic responses have been observed for the new BAMO misfit (incommensurate) layered structure with non-magnetic cations Al^3+ and magnetic cations Mn^3+. The Bi-based layered supercell structures present great composition flexibility and hold great significance towards the design and creation of new two-dimensional layered materials with a wide range of potential functionalities, such as single-phase multiferroic materials, thermoelectrics, and layered materials with tunable band gaps

Reducing Leakage Current and Enhancing Polarization in Multiferroic 3D Super-nanocomposites by Microstructure Engineering

Multiferroic materials have generated great interest due to their potential as functional device materials. Nanocomposites have been increasingly used to design and generate new functionalities by pairing dissimilar ferroic materials, though the combination often introduces new complexity and challenges unforeseeable in single-phase counterparts. The recently developed approaches to fabricate 3D super-nanocomposites (3D‐sNC) open new avenues to control and enhance functional properties. In this work, we develop a new 3D‐sNC with CoFe2O4 (CFO) short nanopillar arrays embedded in BaTiO3 (BTO) film matrix via microstructure engineering by alternatively depositing BTO:CFO vertically-aligned nanocomposite layers and single-phase BTO layers. This microstructure engineering method allows encapsulating the relative conducting CFO phase by the insulating BTO phase, which suppress the leakage current and enhance the polarization. Our results demonstrate that microstructure engineering in 3D‐sNC offers a new bottom–up method of fabricating advanced nanostructures with a wide range of possible configurations for applications where the functional properties need to be systematically modified

Induced ferroelectric phases in SrTiO3 by a nanocomposite approach

Inducing new phases in thick films via vertical lattice strain is one of the critical advantages of vertically aligned nanocomposites (VANs). In SrTiO3 (STO), the ground state is ferroelastic, and the ferroelectricity in STO is suppressed by the orthorhombic transition. Here, we explore whether vertical lattice strain in three-dimensional VANs can be used to induce new ferroelectric phases in SrTiO3:MgO (STO:MgO) VAN thin films. The STO:MgO system incorporates ordered, vertically aligned MgO nanopillars into a STO film matrix. Strong lattice coupling between STO and MgO imposes a large lattice strain in the STO film. We have investigated ferroelectricity in the STO phase, existing up to room temperature, using piezoresponse force microscopy, phase field simulation and second harmonic generation. We also serendipitously discovered the formation of metastable TiO nanocores in MgO nanopillars embedded in the STO film matrix. Our results emphasize the design of new phases via vertical epitaxial strain in VAN thin films

Carbon footprint and driving forces of saline agriculture in coastally reclaimed areas of eastern China: a survey of four staple crops

Carbon emissions have always been a key issue in agricultural production. Because of the specific natural factors in the soil of saline agriculture, there are distinctive characteristics in saline agricultural production as compared with traditional agricultural zones. Here, we have adopted the theory of life cycle assessment, and employed the Intergovernmental Panel on Climate Change (IPCC) greenhouse gas (GHG) field calculation to estimate the GHG emissions, derived from the staple crop productions (i.e., barley, wheat, corn and rice). In addition, our study further analyzed the main driving forces of carbon emissions, and proposed some effective measures to reduce them. Our results have showed that: (1) Carbon footprint from the four crops in the study area varies from 0.63 to 0.77 kg CO2 eq•kg-1, which is higher than that from traditional agriculture; (2) GHG emissions from Fertilizer-Nitrogen (N) manufacture and inorganic N application have contributed to the greatest percentage of carbon footprint. Compared with traditional agricultural zones, fertilizer-N application and paddy irrigation involved with crop productions have overall greater contributions to carbon footprint; (3) Carbon emissions from saline agriculture can be reduced significantly by planting-breeding combination to reduce the amount of N fertilizer application, improving the traditional rotation system, and developing water-saving agriculture and ecological agriculture

Turning antiferromagnetic Sm(0.34)Sr(0.66)MnO3 into a 140 K ferromagnet using a nanocomposite strain tuning approach.

Ferromagnetic insulating thin films of Sm(0.34)Sr(0.66)MnO3 (SSMO) on (001) SrTiO3 substrates with a T(C) of 140 K were formed in self-assembled epitaxial nanocomposite thin films. High T(C) ferromagnetism was enabled through vertical epitaxy of the SSMO matrix with embedded, stiff, ∼40 nm Sm2O3 nanopillars giving a c/a ratio close to 1 in the SSMO. In contrast, bulk and single phase SSMO films of the same composition have much stronger tetragonal distortion, the bulk having c/a >1 and the films having c/a <1, both of which give rise to antiferromagnetic coupling. The work demonstrates a unique and simple route to creating ferromagnetic insulators for spintronics applications where currently available ferromagnetic insulators are either hard to grow and/or have very low T(C).This work was supported by the European Research Council (ERC) (Advanced Investigator grant ERC-2009-AdG-247276-NOVOX). A. Suwardi would also like to acknowledge the Agency for Science, Technology and Research (A*STAR) Singapore for funding his graduate studies. M. E. Vickers is thanked for her help with the X-ray characterization work and A. Sangle for helping with the initial experimental works.This is the author accepted manuscript. The final version is available at http://pubs.rsc.org/en/Content/ArticleLanding/2016/NR/C6NR01037G#!divAbstract

Optimization of Polyaluminum Chloride-Chitosan Flocculant for Treating Pig Biogas Slurry Using the Box–Behnken Response Surface Method

Flocculation can remove large amounts of nitrogen and phosphorus from wastewater, and the resulting nitrogen- and phosphorus-rich floc can be used to produce organic fertilizer. For biogas slurries containing high levels of nitrogen and phosphorus, ordinary flocculants can no longer meet the flocculation requirements. In this study, to fully utilize the advantages of the two flocculants and achieve efficient removal rates of nitrogen and phosphorus from a biogas slurry, chitosan (CTS) and polyaluminum chloride (PAC) were used as a composite flocculation agent to flocculate pig biogas slurries. The response surface method was used to study the effect of PAC added (PACadded) to the composite flocculant (CF), composite flocculant added (CFadded) to the biogas slurry and the pH on flocculation performance, and optimize these three parameters. In the tests, when the PACadded was 6.79 g&middot;100 mL&minus;1CF, the CFadded was 20.05 mL&middot;L&minus;1 biogas slurry and the pH was 7.50, the flocculation performance was the best, with an absorbance of 0.132 at a wavelength of 420 nm. The total phosphorus (TP) concentration was reduced from 214.10 mg&middot;L&minus;1 to 1.38 mg&middot;L&minus;1 for a removal rate of 99.4%. The total ammonia nitrogen (TAN) concentration was reduced from 1568.25 mg&middot;L&minus;1 to 150.27 mg&middot;L&minus;1 for a removal rate of 90.4%. The results showed that the CF could form larger flocs, and had greater adsorption capacity and more stable flocculation performance than ordinary flocculants. Furthermore, the CF could exhibit better chelation, electrical neutralization and bridge adsorption

Finding Group-Based Skyline over a Data Stream in the Sensor Network

Along with the application of the sensor network, there will be large amount of dynamic data coming from sensors. How to dig the useful information from such data is significant. Skyline query is aiming to identify the interesting points from a large dataset. The group-based skyline query is to find the outstanding Pareto Optimal groups which cannot be g-dominated by any other groups with the group same size. However, the existing algorithms of group-based skyline (G-Skyline) focus on the static data set, how to conduct advanced research on data stream remains an open problem at large. In this paper, we propose the group-based skyline query over the data stream. In order to compute G-Skyline efficiently, we present a sharing strategy, and based on which we propose two algorithms to efficiently compute the G-Skyline over the data stream: the point-arriving algorithm and the point-expiring algorithm. In our experiments, three synthetic data sets are used to test our algorithms; the experiments results show that our algorithms perform efficiently over a data stream

Study of the Judder Characteristics of Friction Material for an Automobile Clutch and Test Verification

Abstract The friction judder characteristics during clutch engagement have a significant influence on the NVH of a driveline. In this research, the judder characteristics of automobile clutch friction materials and experimental verification are studied. First, considering the stick-slip phenomenon in the clutch engagement process, a detailed 9-degrees-of-freedom (DOF) model including the body, each cylinder of the engine, clutch and friction lining, torsional damper, transmission and other driveline parts is established, and the calculation formula of friction torque in the clutch engagement process is determined. Second, the influence of the friction gradient characteristics on the amplification or attenuation of the automobile friction judder is analyzed, and the corresponding stability analysis and the numerical simulation of different friction gradient values are carried out with MATLAB/Simulink software. Finally, judder bench test equipment and a corresponding damping test program are developed, and the relationship between the friction coefficient gradient characteristics and the system damping is analyzed. After a large number of tests, the evaluation basis of the test is determined. The research results show that the friction lining with negative gradient characteristics of the friction coefficient will have a judder signal. When the friction gradient value is less than −0.005 s/m, the judder signal of the measured clutch cannot be completely attenuated, and the judder phenomenon occurs. When the friction gradient is greater than − 0.005 s/m, the judder signal can be significantly suppressed and the system connection tends to be stable

Effect of cooling rate on the size fluctuation of V-containing phases in Al-V master alloys

To investigate the relationship between the solidification cooling rate and the size fluctuation of different V-containing phases, Al-4 wt. % V master alloys with various V-containing constituents were prepared at different cooling rates carried out by a wedge-shaped water-cooled copper mold, a graphite mold and a refractory mold at 1050°C, respectively. The variance of lognormal density function was used to characterize the size fluctuation of V-containing phases quantitatively. The results show that the largest size difference of both Al10V phases and Al3V phases is simultaneously present in the ingot prepared by the average solidification cooling rate of 2°C·s-1, while the smallest difference of Al10V phases in size is present in the ingot prepared by the average solidification cooling rate of 271°C·s-1. The size fluctuation of the Al3V phases first increases slightly and then decreases with increasing average solidification cooling rate in the range of 30~195°C·s-1