Chongde Cao

Acoustic method for levitation of small living animals

Ultrasonic levitation of some small living animals such as ant, ladybug, and young fish has been achieved with a single-axis acoustic levitator. The vitality of ant and ladybug is not evidently influenced during the acoustic levitation, whereas that of the young fish is reduced because of the inadequacy of water supply. Numerical analysis shows that the sound pressures on the ladybug’s surface almost reach the incident pressure amplitude p0 due to sound scattering. It is estimated that 99.98% of the acoustic energy is reflected away from the ladybug. The acoustic radiation pressure pa on the ladybug’s surface is only 1%–3% of p0, which plays a compression role on the central region and a suction role on the peripheral region.Ultrasonic levitation of some small living animals such as ant, ladybug, and young fish has been achieved with a single-axis acoustic levitator. The vitality of ant and ladybug is not evidently influenced during the acoustic levitation, whereas that of the young fish is reduced because of the inadequacy of water supply. Numerical analysis shows that the sound pressures on the ladybug’s surface almost reach the incident pressure amplitude p0 due to sound scattering. It is estimated that 99.98% of the acoustic energy is reflected away from the ladybug. The acoustic radiation pressure pa on the ladybug’s surface is only 1%–3% of p0, which plays a compression role on the central region and a suction role on the peripheral region.

Thermophysical properties of a highly superheated and undercooled Ni–Si alloy melt

The surface tension of superheated and undercooled liquid Ni–5 wt % Si alloy was measured by an electromagnetic oscillating drop method over a wide temperature range from 1417 to 1994 K. The maximum undercooling of 206 K (0.13 TL) was achieved. The surface tension of liquid Ni–5 wt % Si alloy is 1.697 N m−1 at the liquidus temperature 1623 K, and its temperature coefficient is −3.97×10−4 N m−1 K−1. On the basis of the experimental data of surface tension, the other thermophysical properties such as the viscosity, the solute diffusion coefficient, and the density of liquid Ni–5 wt % Si alloy were also derived.

Microstructural characterization of cobalt–antimony eutectic alloy droplets solidified in drop tube

Abstract Co–Sb alloy droplets have been solidified during free fall in a 3 m drop tube. The cooling rate and undercooling are estimated versus droplet diameter, both of which play a dominant part in dendritic and eutectic growth. The eutectic coupled zone has been calculated on the basis of TMK and LKT/BCT theories, which covers a composition range from 22.7% to 49%Sb. A ‘lamellar-anomalous’ eutectic transition occurs to Co-41.4%Sb droplets with the increase of undercooling. For Co-20%Sb hypoeutectic alloy, primary α-Co phase experiences a ‘dendritic to equiaxed’ structural morphology transition and an abrupt grain refinement at a critical undercooling of about 88 K under drop tube conditions. The remaining interdendritic liquid does not solidify in a mode of eutectic growth but forms into a divorced structure under drop tube conditions. The primary β-CoSb intermetallic compound of Co-45%Sb hypereutectic alloy grows in a dendritic way inside droplet and forms as a spherical shell on droplet surface. Most Co-45%Sb droplets undercooled by 80∼130 K exhibit complete eutectic microstructures. Significant solute trapping takes place in primary α-Co and β-CoSb dendrites.

Surface tension of superheated and undercooled liquid Co–Si alloy

The surface tension of superheated and undercooled liquid Co 25wt.% Si alloy was measured by an electromagnetic oscillating drop method. The experimental temperature regime was from 1384 to 2339K and a maximum undercooling of 223K (0.14TL) was achieved. The surface tension of liquid Co 25wt.% Si alloy is 1.604Nm−1 at the liquidus temperature of 1607K, and its temperature coefficient is −4.0×10−4Nm−1K−1. On the basis of previous research results of pure Co and Si, an expression is developed to predict the surface tension of binary Co–Si alloy system. The other thermophysical properties, such as the viscosity, the solute diffusion coefficient, and the density of liquid Co 25wt.% Si alloy are also derived by the relevant theoretical models.

Crystallization and Corrosion Resistance of (Fe0.78Si0.09B0.13)100-xNix (x=0, 2 and 5) Glassy Alloys

The crystallization of the (Fe0.78Si0.09B0.13)100-xNix glassy alloys (x=0, 2 and 5) has been investigated by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). Corrosion resistance analyses have been carried out using electrochemical measurements and corrosion products have been analyzed by scanning electron microscopy (SEM). The experimental results show that the addition of Ni can promote the nucleation of α-Fe, retard the decomposition of the metastable borides, and alter the crystallization mode of the present Fe-based glassy alloys. The lattice constant (αFe0) of α-Fe in the annealed samples shows a decreasing trend with increasing annealing time. The Ni addition can improve the corrosion resistance of the as-quenched Fe-based glassy alloys in H2SO4, NaCl and NaOH solutions. The results indicate that Ni can promote the diffusion of Si atoms during quenching and annealing processes.

A Mott insulator continuously connected to iron pnictide superconductors

Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe1−xCuxAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5, the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ∼x=0.05. Our discovery of a Mott-insulating state in NaFe1−xCuxAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-Tc superconductivity.

Distinct itinerant spin-density waves and local-moment antiferromagnetism in an intermetallic ErPd2Si2 single crystal.

Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix.

Rapid solidification of Cu60Co30Cr10 alloy under different conditions

Abstract Metastable liquid phase separation and rapid solidification in a metastable miscibility gap were investigated on the Cu 60 Co 30 Cr 10 alloy by using the electromagnetic levitation and splat-quenching. It is found that the alloy generally has a microstructure consisting of a (Co,Cr)-rich phase embedded in a Cu-rich matrix, and the morphology and size of the (Co,Cr)-rich phase vary drastically with cooling rate. During the electromagnetic levitation solidification processing the cooling rate is lower, resulting in an obvious coalescence tendency of the (Co,Cr)-rich spheroids. The (Co,Cr)-rich phase shows dendrites and coarse spheroids at lower cooling rates. In the splat quenched samples the (Co,Cr)-rich phase spheres were refined significantly and no dendrites were observed. This is probably due to the higher cooling rate, undercooling and interface tension.

Crystalline structure and dielectric properties of multiferroic Cr-doped YMnO3

AbstractYMn0.9Cr0.1O3 polycrystalline material was synthesized by conventional solid-state reaction method. The crystalline structure and dielectric properties of YMn0.9Cr0.1O3 were investigated. YMn0.9Cr0.1O3 ceramic is proved to be a hexagonal structure with P63cm space group by the X-ray diffraction. The temperature dependence of dielectric constant and loss curves indicate YMnO3 and YMn0.9Cr0.1O3 samples exhibit an obvious dielectric relaxation behavior at low temperature range. The frequency dependence of dielectric loss peak follows an Arrhenius law. The XPS analysis suggest that the increase in valence compensation and the decrease in oxide vacancy compensation cause lower dielectric constant in the Cr doped YMn0.9Cr0.1O3 sample.

Peculiarities of anisotropic electrical resistivity in Lu2PdSi3 single crystals

Lu2PdSi3 represents a non-magnetic member of the class of R2PdSi3 intermetallic compounds (R = rare earths) with hexagonal AlB2-type crystallographic structure. The electrical resistivity of single crystalline Lu2PdSi3 is highly anisotropic and reflects metallic behaviour. Its temperature dependence follows the Bloch–Gruneisen law for c-axis orientation [001]. For [100] orientation in the perpendicular plane the observed deviation from the Bloch–Gruneisen law can be explained by the Ioffe–Regel criterion. The relatively low Debye temperature ΘD of the order of 200 K fairly well agrees with that derived from specific heat data of Lu2PdSi3. Notably, Lu2PdSi3 allows extracting the magnetic entropy contribution of isostructural R2PdSi3 compounds.