Crystal Growth, Structural and Optical Studies of CuGa3Se5 Bulk Compounds

Bulk materials were synthesized by the Bridgman technique using the elements Cu, Ga, Se. These samples were characterized by Energy Dispersive Spectrometry (EDS) to determine the elemental composition, as well as by X-ray diffraction for structure, hot point probe method for type of conductivity. Optical response (Photoconductivity) and Photoluminescence (PL) and PL-excitation (PLE) at temperatures from 4.2 to 77 K were also used to estimate the band-gap energy of Cu-Ga3Se5. They show a nearly perfect stoechiometry and present p-type conductivity. CuGa3Se5 either have an Ordered Defect Chalcopyrite structure (ODC), or an Ordered Vacancy Chalcopyrite structure (OVC). The gap energy obtained by Photoconductivity and Photoluminescence (PL) for the different samples is 1.85 eV. Studying the variation of the gap as a function of the temperature shows that the transition is a D-A type. The defects that appear are probably GaCu.

Effect of heat treatment on microstructures and mechanical properties of a bulk nanostructured Al-Zn-Mg-Cu alloy

A bulk nanostructured Al-10.0Zn-2.8Mg-1.8Cu alloy was synthesized by cryomilling first and then by spark plasma sintering （SPS）, and the effect of heat treatment on the microstructures and mechanical properties of this alloy were studied. Most MgZn2 particles with a coarse size lie on the grain boundaries of the SPS-processed sample. After solid solution and artificial aging, fine spherical-like MgZn2 particles precipitate uniformly in the grain interiors. No obvious grain growth is found after the heat treatment. A nanoindentation study indicates that no clear change is found in the Yong＇s modulus of the nanostructured alloy after the heat treatment. However, the hardness of the nanostructured alloy increases by about 33% after the heat treatment, which is attributed to the effect of precipitation-hardening.

Unreacted equation of states of typical energetic materials under static compression:A review

The unreacted equation of state（EOS） of energetic materials is an important thermodynamic relationship to characterize their high pressure behaviors and has practical importance. The previous experimental and theoretical works on the equation of state of several energetic materials including nitromethane, 1,3,5-trinitrohexahydro-1,3,5-triazine（RDX）,1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane（HMX）, hexanitrostilbene（HNS）, hexanitrohexaazaisowurtzitane（HNIW or CL-20）, pentaerythritol tetranitrate（PETN）, 2,6-diamino-3,5-dinitropyrazine-1-oxide（LLM-105）, triamino-trinitrobenzene（TATB）, 1,1-diamino-2,2-dinitroethene（DADNE or FOX-7）, and trinitrotoluene（TNT） are reviewed in this paper. The EOS determined from hydrostatic and non-hydrostatic compressions are discussed and compared. The theoretical results based on ab initio calculations are summarized and compared with the experimental data.

Ionic Conductivity of Nano-LaF_3 Bulk Material at Room Temperature

Nanocrystalline powder of LaF3 was synthesized by a method of direct precipitation from water solution. Particle size and shape of LaF3 nanocrystalline powder was analysed with TEM. Particles were mainly spherical with narrow particle size distribution （10 20 nm）. The average particle size analysed with XRD is 16.7 nm. Nano-LaF3 bulk material was prepared by compacting the powder to 1 GPa at room temperature and a vacuum of 10^-4 Pa. The ionic conductivity of nano-LaF3 bulk material was studied with complex impedance spectra at room temperature. The ionic conductivity of nano-LaF3 bulk material （1 × 10^-5 S·cm^-1 ） at room temperature is significantly increased compared to that of single crystal LaF3 （1 × 10^-6 S·cm^-1）. A special phenomenon was observed firstly time that the ionic conductivity increased gradually with multiple testing in result of relaxation.

EXPERIMENTAL STUDY ON ULTRAFINE COMMINUTION IN THEORY OF VERTIGINOUS CURRENT OF BULK MATERIAL

Experiment about ultrafine comminution in theory of vertiginous current of bulk material has successfully performed by a lately developed vertical shaft centrifugal autogenous grinder. The results of tested several materials are analyzed, moreover. the comminution mechanism and the affecting factors of ultrafine comminution are analyzed.

Investigation on Rapidly Solidified T15 High Speed Steel Powder and Its Bulk Microcrystalline Material

Authors produced rapidly solidified T15 high speed steel powders by high pressure(5~ 6MPa) N_a atomization and liquid N_2 cooling,observed and analyzed the morphology and structure of the powders;at the same time,prepared bulk microcrystalline T15 high speed steel materials by hot extruding or HIPing and hot rolling of the powders,observed and measured the microstructure and performance of the bulk materials.It was shown that rapid solidification may change the solidification characteristics and structure of T15 high speed steel powder and improve the qualities and properties of T15 high speed steel materials.

THE SELF-GRINDING MECHANISM AND AFFECTING FACTORS OF BULK MATERIAL IN FLUID MOTION

The fluidity and classification of bulk material (loose body) were introduced, the self-grinding mechanism and the affecting factors of bulk materials in various forms of phase, state and motion were investigated. A rotational-flow-state centrifugal autogenous grinder was developed on the basis of applying self-grinding mechanism of bulk material,the result tested by the autogenous grinder was compared with that tested by 4R Raymond mills, and fine particles with extremely high specific area were obtained. The feasibility of the developed new-type autogenous grinder in the view of fluid motion of bulk material was proved.

What are the practical limits for the specific surface area and capacitance of bulk sp^2 carbon materials?

The possible practical limits for the specific surface area and capacitance performance of bulk sp^2 carbon materials were investigated experimentally and theoretically using a variety of carbon materials. We find the limit for the specific surface area to be 3500–3700 m^2 g^(-1), and based on this, the corresponding best capacitance was predicted for various electrolyte systems. A model using an effective ionic diameter for the electrolyte ions was proposed and used to calculate the theoretical capacitance. A linear dependence of experimental capacitance versus effective specific surface area of various sp^2 carbon materials was obtained for all studied ionic liquid, organic and aqueous electrolyte systems. Furthermore, excellent agreement between the theoretical and experimental capacitance was observed for all the tested sp^2 carbon materials in these electrolyte systems, indicating that this model can be applied widely in the evaluation of various carbon materials for supercapacitors.

Grain size reduction of copper subjected to repetitive uniaxial compression combined with accumulative fold

This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction （XRD）, respectively. Our results show that the average grain size of samples decreases from about 830 nm to 127 nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.

D-A structural protean small molecule donor materials for solution-processed organic solar cells

Under the synergistic effect of molecular design and devices engineering, small molecular organic solar cells have presented an unstoppable tendency for rapid development with putting forward donor- acceptor （D-A） structures. Up to now, the highest power conversion efficiency of small molecules has exceeded 11%, comparable to that of polymers. In this review, we summarize the high performance small molecule donors in various classes of typical donor-acceptor （D-A） structures and discuss their relationships briefly.

Extremely low thermal conductivity from bismuth selenohalides with 1D soft crystal structure

Materials with intrinsically low thermal conductivity are of fundamental interests.Here we report a new sort of simple one-dimensional(1 D)crystal structured bismuth selenohalides(Bi Se X,X=Br,I)with extremely low thermal conductivity of^0.27 W m^-1K^-1 at 573 K.The mechanism of the extremely low thermal conductivity in 1 D Bi Se X is elucidated systematically using the first-principles calculations,neutron powder-diffraction measurements and temperature tunable aberration-corrected scanning transmission electron microscopy(STEM).Results reveal that the1 D structure of Bi Se X possesses unique soft bonding character,low phonon velocity,strong anharmonicity of both acoustic and optical phonon modes,and large off-center displacement of Bi and halogen atoms.Cooperatively,all these features contribute to the minimal phonon transport.These findings provide a novel selection rule to search low thermal conductivity materials with potential applications in thermoelectrics and thermal barrier coatings.

Accelerated exploration of TRIP metallic glass composite by laser additive manufacturing

Introducing transformation-induced plasticity(TRIP)effect into bulk metallic glass composites(BMGCs)is an effective route to improve their ductility and strain-hardening ability.Since the morphology and structure of the crystalline austenite phases responsible for the TRIP phenomenon are strongly dependent on the alloy composition and cooling rate during freezing,distinguishing the optimal cases from a vast variety of candidates is the primary task of exploring TRIP BMGCs.However,without a suitable theoretical guidance,the exploration of BMGCs is usually performed via the traditional trial-and-error route,making the BMGC development extremely time consuming and labor intensive.Here,we present a novel high-throughput strategy to accelerate the exploration process of TRIP BMGCs.The efficiency of this strategy was demonstrated on a well-studied Cu-Zr-Al alloy system.A screening library,comprised by121 cylindrical samples with different conditions,was rapidly prepared by laser additive manufacturing(LAM).The phases of the library were efficiently identified by micro-area X-ray diffraction(M-XRD)to screen the optimal compositions and cooling rates that precipitate only B2-Cu Zr phase.The distribution uniformity of the B2-Cu Zr phase was further evaluated based on digital image processing technology to screen the candidates of better ductility.The high-throughput results are in good agreement with the previous casting investigations of discrete samples,confirming the validity of the present high-throughput strategy.