AC Conductivity of (As_2Te_3)_(100-x)Ge_x Bulk Glassy System

The ac conductivity of the bulk amorphous chalcogenide system (As2Te3)100-xGex (where x=0,5,10,15 and 25 at. pct) was investigated at variable frequencies ranging from 50 Hz to 100 kHz and at different temperatures ranging from 3O to 160℃. lt was found that at a fixed temperature, where n <1 and decreases with temperature. The complex impedence Z was measured over the same frequency and temperature ranges. All samples give a semicircle arc originating at the origin point. This indicates that each composition can be described only by one resistance R and one capacity C, both parallelly combined. The centre below the real axis indicates the relaxation behaviour of the system. The activation energies for conduction were calculated.     

The Tb Doping Effect on the Room Temperature Magnetoresistance in (La1-xTbx)0.67Sr0.33MnO3 (x≤ 0.4)

by Tb in (La1-xTbx)0.67Sr0.33MnO3, the room temperature magnetoresistance △R/R0 drops at first, then undergoes an increase near x≈0.1, and finally drops again. The value of room temperature magnetoresistance at a field H=12 kOe for (La1-xTbx)0.67Sr0.33MnO3 is -3.56%. The enhancement of the room temperature magnetoresistance induced by an appropriate Tb substitution in (La1-xTbx)0.67Sr0.33MnO3 is correlated with the shifts of the Curie temperature and metal-insulator temperature to near room temperature. The drop of the room temperature magnetoresistance at large Tb doping-contents may be due to its lower TC and TMI far from the room temperature.     

The Tb Doping Effect on the Room Temperature Magnetoresistance in(La_(1-x)Tb_x)_(0.67)Sr_(0.33)MnO_3(x≤0.4)

With substitution of La by Tb in (La_(1-x)Tb_x)_(0.67)Sr_(0.33)MnO_3, the room temperature magnetoresistance △R/R_0drops at first, then undergoes an increase near x≈0.1, and finally drops again. The value of room temperaturemagnetoresistance at a field H=12 kOe for (La_(0.9)Tb_(0.1))_(0.67)Sr_(0.33)MnO_3 is -3.56%. The enhancement of the roomtemperature magnetoresistance induced by an appropriate Tb substitution in (La_(1-x)Tb_x)_(0.67)Sr_(0.33)MnO_3 is correlatedwith the shifts of the Curie temperature and metal-insulator temperature to near room temperature. The drop ofthe room temperature magnetoresistance at large Tb doping-contents may be due to its lower T_C and T_(MI) far fromthe room temperature.     

Electrical Relaxation in Mixed Alkali Bi2O3-K2O-Li2O-Fe2O3 Glasses

A new glass system(Bi2O3)50(Fe2O3)10(Li2O)x(K2O)40-x, where x changes in steps of 5 mole fraction between 0 and 40, was selected to study the electrical relaxation and the mixed alkali effect(MAE)phenomena.Measurements of ac conductivity σac, dielectric permittivity ε' and loss factor tanδ in the frequency range of 0.12～102 kHz and in the temperature range of 300～650 K were carried out. The temperature dependence of the ac conductivity shows a slow increasing rate at low temperature and high frequency and a rapid increase at high temperature and low frequency. At constant temperature, the ac conductivity is found to be proportional to ωs, where s is the frequency exponent, which is less than 1. Analysis of the conductivity data and the frequency exponent shows that the overlapping large polaron tunnelling(OLPT)model of ions is the most favorable mechanism for the ac conduction in the present glass system. The ac response, the dc conductivity and dielectric relaxation have the same activation energy and they originate from the same basic transport mechanism. The results of the dielectric permittivity show no maximum peak in the temperature and frequency range studied. This absence of maximum peak is an indication of non-ferroelectric behavior of all the studied samples. The MAE has been detected in the ac conductivity, which is the same as the classical MAE in the dc conductivity. The electrical parameters such as dielectric permittivity ε' and real dielectric modulus M'show a typical minimum deviation from linearity by about two orders of magnitude. The loss factor tanδ and the imaginary dielectric modulus M" are insignificantly dependent on composition even at the same transition temperature Tg.     

Effect of Deposition Temperature on Dynamics and Mechanism of Deposition for Si-B-C Ceramic from BCl3/SiCH3Cl3/H2 Precursor

The deposition rate, phase, chemical composition and microstructure of deposits were determined from 950 to 1100℃. With increasing temperature, the deposition rate increases, and the morphology changes from smooth to coarse, meanwhile, the concentration of silicon increases while that of boron decreases. The deposition process is controlled by chemical reactions, and the activation energy is 271 kJ/mol. At relatively lower temperature (below 1000℃), the deposition process is dominated by formation of B4C. While at higher temperature (above 1000℃), it is governed by formation of SiC. B4C and SiC disperse uniformly in the Si-B-C co-deposition system and form a dense network structure.     

Preparation and Superconducting Properties of F-doped SmO_(1-x)F_xFeAs

Here we report the fabrication and superconductivity of the iron-based arsenic oxide SmO1-xFxFeAs compound.X-ray diffraction(XRD) results prove that the lattice parameters a and c decrease systematically with increasing x in between 00.35 the a and c increase with the decrease of x in the SmO1-xFxFeAs.The critical temperature(Tc) increases with increasing x in between 0.15≤x≤0.3,while x>0.3 the Tc decreases with the increase of x.It is found that at x=0.3 SmO0.7F0.3FeAs has the highest onset resistivity transition temperature of 55.5 K.The critical current density(Jc) value at 10 K for the obtained SmO0.7F0.3FeAs is 1.3×10 5 A/cm2(0T).Meanwhile one can estimates Hc2(0) from the slope of the Hc2(T) curve at T =Tc(HC2 is the upper critical field),and for the 90% normal-state resistivity(ρn) criterion(Tc=55 K),Hc2(0) is determined to be ～253 T.     

Dependence of Structural and Optoelectrical Properties on the Composition of Electron Beam Evaporated Zn_xCd_(1-x)S Thin Films

Thin films of ZnxCd1-xS have been prepared by electron beam evaporation of a mixture of ZnS & CdS powders. The films are deposited onto sodalime glass slides under similar conditions.The composition of the films is varied from CdS to ZnS (x=0 to 1). The films show a regular change in color from toner red to orange yellow as Zn concentration increases to maximum.These films are characterized for their optical, electricaI and structural properties. The bandgap value of ZnxCd1-xS films is found to vary linearIy from 2.20 eV to 3.44 eV with change in the x value from 0 to 1. The resistivity of these films is in the range of 171.0 Ωcm to 5.5× 106Ωcm for x=0~0.6. All the samples show cubic structure after annealing in air at 250℃ for 40 min.The lattice constant ao varies from 0.5884 nm to 0.54109 nm linearly.     

γ-Fe Nano-particles from Fe(CO)_5 by CW CO_2 Laser-driven

γ-Fe nano-particles with size of 20-40 nm were produced by SF6-sensitized CW CO2 laser-induced gaseous pyrolysis of Fe(Co) 5, The γ-Fe stabte in reaction zone at above 910℃ was formed.The rapid quenching prevents from the γ-Fe transforming to α-Fe as rapidly cooling from high temperature to room temperature, The characteristics of the particles were examined at room temperature by TEM. electron diffraction and XRD. It was proved that about 70% of γ-Fe phase in the particles was present. In addition. the lattice constant of the γ-Fe was 0.364 nm in place of 0.360 nm     

In-situ Synthesis and Formation Mechanism ofTiN-Al_2O_3/Al Composite

The synthesis of TiN and Al2O3 by in situ injection of reactive nitrogen gas into molten Al alloys has been evaluated over the temperature range from 1000 to 1600℃. It is shown that TiN and Al2O3 can be formed in melt with nitrogen and surplus oxygen (in vacuum room of the induction furnace) as the reactive gases over 1000℃. Up to 2.1 wt pct Al2O3 and 5.2 wt pct of TiN in situ phases in an Al alloy has been formed in a range of size from 0.8 to 5 μm. The formation mechanism of TiN and Al2O3 is discussed in this paper.     

Synthesis and Structure Transformation of Orthorhombic LiMnO2 Cathode Materials by Sol-gel Method

Orthorhombic LiMnO2 cathode materials were synthesized successfully at lower temperature by sol-gel method. When LiMnO2 precursor prepared by sol-gel method was fired in air, the product was a mixture of spinel structure LiMn2O4 and rock-salt structure Li2MnO3, whereas in argon single-phase orthorhombic LiMnO2 could obtain at the range of 750℃ to 920℃. The substitution of Mn by Zn2+ or Co3+ in LiMnO2 led to the structure of LiMnO2 transiting to Qα-LiFeO2. The results of electrochemical cycles indicated that the discharged capacity of orthorhombic-LiMnO2 was smaller at the initial stages, then gradually increased with the increasing of cycle number, finally the capacity stabilized to certain value after about 10th cycles. This phenomenon reveals that there is an activation process for orthorhombic LiMnO2 cathode materials during electrochemical cycles, which is a phase transition process from orthorhombic LiMnO2 to tetragonal spinel Li2Mn2O4. The capacity of orthorhombic LiMnO2 synthesized at lower te     

Effect of Heat Treatment on the Microstructure and Residual Stresses in (Ti,Al)N Films

(Ti,Al)N films were fabricated by arc ion plating (AIP) and then annealed within a range of temperatures from 200 to 500~0C for 30 min in vacuum. The results indicate that the average residual stresses decrease slightly from -5.84 to -4.98 GPa with increasing annealing temperature. The stress depth distribution evolves from a sharp "bell" shape to a mild "bell" shape, suggesting a more uniform stress state in the annealed films. The microstructure of the films was also investigated in detail. The as-deposited film consists of fine columnar crystals with an amorphous phase at the interface. During heat treatment, the columnar subgrain growth was observed; meanwhile, the phenomenon of crystallization has been identified at the interface. Further more, the relationship between the residual stresses and the microstructure of the films was explored and highlighted. In addition, there is no hardness degradation of the films during heat treatment.     

Synthesis and Characterization of Sm_xGd_yCe_(1-x-y)O_(2-δ) Nanopowders

SmxGdyCe1-x-yO2-δ (x+y=0.2 and x=0, 0.04, 0.08, 0.12, 0.16, 0.2) nanopowders were prepared by a copre-cipitation method. The zeta potential and sedimentation volume of Ce(OH)4 aqueous dispersions at different pH values were measured. The isoelectric point (IEP) of Ce(OH)4 suspensions is 7.0. The maximum potential value of -18.5 mV and maximum sedimentation volume of 19 ml are reached at pH=10. The evolution behaviors of the xSm(OH)3·yGd(OH)3·(1-x-y)Ce(OH)4 dried powders in the heating process was characterized by DTA/TG and XRO. The powders decompose to ceria based solid solution at a temperature below 300℃ and forms cubic fluorite structure ceria at about 650℃. The properties of SmxGdyCe1-x-yO2-δ solid solutions were characterized by XRD, TEM and BET. The lattice parameter of doped Ce02 increases linearly with increasing Sm3+ substitution (or decreasing Gd3+ substitution). The particle size of the doped ceria powders is from 5 nm to 10 nm.     

Formation and Properties of Nanocrystalline (Fe_(0.99)Mo_(0.01))_(78)Si_9B_(13) Alloy

Polycrystalline Fe-Mo-Si-B alloys with grains sized from 15 to 200 nm were prepared by means ofthe crystallization method. A critical phenomenon was observed in the variations of microhardnessand electrical resistivity with respect to the annealing temperature. The critical temperature is 893 Kwhich corresponds to the average grain size of 45 nm.     

Growth and Solvent Effects of a Promising Nonlinear Optical Sodium Paranitrophenolate Dihydrate (NO_2-C_H_4-ONa·2H_2O) Single Crystal

Sodium paranitrophenolate dihydrate (NPNa·2H2O) is an excellent semiorganic nonlinear optical (NLO) material, crystallizes both in water and methanol with high degree of transparency. Good optical quality single crystals of dimension upto 18 mm×6 mm×3 mm are obtained by isothermal solvent evaporation technique. The solubility of the crystal in different solvents was measured gravimetrically. The single crystals of NPNa·2H2O show variation in physical properties and growth rate in different solvents. Methanol or ethanol solution yields crystals of bipyramidal shape with clear morphology. However, methanol grown crystal is exhibiting improved hardness parameters and possesses excellent thermal stability as compared to water grown crystals. The effects of solvent on hardness parameter along with thermal and optical properties of NPNa·2H2O was revealed in this paper.     

Fabrication of Al/Al2O3 composites and FGM

Al/Al2O3 composites of different ratios were hot-press sintered at 575 similar to 640℃ under a pressure of 30 MPa for 2 h in a vacuum furnace. It was found that the relative density of the Al/Al2O3 composites could be increased evidently with the rise of sinter temperature. No reaction occurred between Al and Al2O3 at the sinter temperatures. Under 640℃-30 MPa-2 h experimental condition, Al/Al2O3 system FGM was successfully fabricated, and its density range changed quasi-continuously from 2.887x10(3) kg/m(3) to 3.1909x10(3) kg/m3 within the middle 1.0 mm thickness range.     

Effect of Seed Sizes on Growth of Large Synthetic Diamond Crystals

For the growth of large synthetic diamond crystals by temperature gradient method （TGM）, the grit sizes of seed crystals have great effects on the growth rate and quality of large grown crystals. Because of the limited area of seed surfaces, the maximum diffusion flux of carbon source, which could be absorbed by the seed, is related to the seed size. And with increasing the seed sizes, the growth rates also increase markedly. However, the seed sizes should be lower than a certain value, which determines the crystal quality directly. For example, with NiMnCo alloy as the metal solvent, when the seed size increases from 0.5 to 1.8 mm, the growth rate increases greatly from about 1.1 to 3.2 mg/h; when the size is beyond 2.0 mm, more and more metal inclusions would be incorporated into the grown crystals, and the crystal quality is destroyed heavily. Finite element analysis （FEA） shows that, due to the special assembly of growth cell, the diffusion of carbon source in the metal solvent is very inhomogeneous, which could be substantiated directly by the appearances and shapes of large grown crystals and the remains of carbon source. And this inhomogeneous diffusion of carbon source would be very harmful to the growth of large diamond crystals, especially when large-size seed crystals are used.     

Dendritic Deposition of NH_4CI Crystals with Free Surface as Simulations of Surface Solidification of Materials

As a simulation of surface solidification of materials,quasi-two dimensional dendritic deposition ofammonium chloride(NH_4Cl)crystals from an aqueous solution film with free surface byvapourization was investigated by the in- situ observation technique.The depositing morphologiesof NH_4Cl crystals are faceted and of growth laws differing from the three-dimensional case.Underlow supersaturation,faceted dendrites formed,whereas the anisotropy in growth kinetics decreaseswith the increase of supersaturation.When vapourizing rate(supersaturation)is not very low,oscillations of growth rate.tip-radius and second arm spacing of the dendrites were observed.It issuggested that this dynamic phenomenon is attributed to the correlation between theconvection-transfer effect induced by the surface tension gradient of solution film.and the drivingforce for deposition.     

Hot Deformation Characteristics for a Nickel-base Superalloy GH742y

The hot deformation characteristics of as-cast nickel-base superalloy GH742y after hot isostatic pressing (HIP)(hereafter referred to as-cast alloy) have been investigated by hot compression tests in the temperature range of 1050 to 1140℃, strain rate range of 0.01 s-1 to 10 s-1 and strain range of 35% to 50% by means of Gleeble-3500 thermal mechanical simulator.The results show that the as-cast alloy exhibits the poor deformability, and shows wedge-shaped cracking beyond the strain of 35%.At strain rates less than 1.0 s-1,the stress-strain curves exhibit nearly steady-state behavior, while at strain rate of 10 s-1, a yield drop and serrated yielding occur.The activation energy values developed on the basis of the experimental data are divided into three domains.The first domain appears at lower strain rate (≤1.0 s-1) and lower temperature (≤1080℃), with the lowest mean value of activation energy about 261.4 kJ/mol.The second domain appears at the same strain rate as the first domain, but higher temperature (>1080℃), with the intermediate mean value of activation energy about 328.8 kJ/mol.The third domain appears at higher strain rate (10 s-1) and temperature range of 1050 to 1140℃, with the largest mean value of activation energy about 605.05 kJ/mol.Three different constitutive equations are established in corresponding to domains.Microstructural observations in the third domain reveal non-uniform dynamic recrystallization (DRX) of homogeneous γ phase, which leads to the poor deformability and the highest Q value.In contrast, microstructures in the first domain show fully DRX of homogeneous γ phase, leading to the better deformability and the lowest Q value.It is noted that the grain size increases with the increment of strain rate or temperature.These results suggest that bulk metal working of this material may be carried out in the first domain where fully DRX of γ homogeneous occurred.     

Low Ductility at Elevated Temperatures of the Cryogenic and Non-magnetic Steel Fe-23Mn-4Al-SCr-0.3C

The origin of low ductility at elevated tempera-ture in the cryogenic and non-magnetic steelFe-23Mn-4Al-5Cr-0.3C was investigated bymeans of impact test at elevated temperatures,opti-cal microscope,SEM and TEM.The experimentalresults indicate that the impact toughness lowerswith increasing testing temperature,and exhibits alow trough of ductility from 865℃ to 1050℃ and apeak value at 1150℃.The intergranular fractureoccurs in the temperature region of low ductilityand the transgranular ductile rupture below this re-gion principally.There is a process of precipitating,gathering,growing,and dissolution of carbide(FeMnCr)_(23)C_6 and AlN between 500℃ and1000℃.The coalescence of microvoids caused bythe process at grain boundaries results in theintergranular fracture and the low ductility at ele-vated temperatures.     

Effects of In-situ Generated Coinage Nanometals on Crystallization and Microstructure of Fluorophlogopite Mica Containing Glass-Ceramics

The effects of in-situ generated coinage nanometals(Cu,Ag and Au) on crystallization behavior,microstructure,thermal and mechanical properties of SiO_2-MgO-Al_2O_3-B_2O_3-K_2O-MgF_2(BMAPS) glassceramics were systematically studied.On addition of coinage nanometai,the glass transition temperature(T_g) is increased by 20-30 ℃,crystallization temperature(T_c) by 30-50 ℃ and dilatometric softening temperature(T_d) by 10-25 ℃.It was found that the density of Cu-containing glass was 2.59 g cm~(-3) and for other glasses it was in the range of 2.56-2.57 g cm~(-3).From the non-isothermal differential scanning calorimetry study,the activation energy of crystallization for BMAPS base glass was calculated as 344 kJ/mol,and changed to 406,334 and 274 kJ/mol on addition of Cu,Ag and Au-nanometals,respectively.Crystals evolved in the opaque BMAPS glass-ceramics derived by controlled heat treatment,were identified as fluorophlogopite mica(KMg_3(AlSi_3O_(10))F_2) by X-ray diffraction(XRD) technique and confirmed by Fourier transformed infrared spectroscopy.Presences of copper,silver and gold nanometals were also identified by XRD technique.It is found from field emission scanning electron microscopy that the interlocked grain like microstructure developed in BMAPS glass-ceramics(being heat-treated at 1050 ℃ for 4 h) changed to denser house-of-cards like microstructure(containing smaller sized mica crystals) on addition of coinage nanometals.Density of BMAPS base glass-ceramic was 2.60 g cm~(-3) and marginally changed to 2.61-2.62 g cm~(-3) on addition of Cu,Ag and Au-nanometals.The change in microstructure resulted in the decrease of Vickers micro hardness value from 5.37 to 4.12,4.20 and 4.58 GPa on addition of Cu,Ag and Au,respectively.Coinage nanometai doped mica glass-ceramics containing interlocked microstructure with higher thermal expansion coefficient,hence,is suitable for high temperature sealing application(like solid oxide fuel cell).