Synthesis and characterization of indium intercalation compounds of tungsten disulphide: InxWS2 (0 ⩽ x ⩽ 1)

The present work reports on the synthesis of indium intercalation compounds In_xWS₂ (0 ? x ? 1). The material has been characterized by X-ray studies for structure determination and particle size distribution, room temperature magnetic susceptibility, thermoelectric power experiments and conductivity measurements in the temperature range 150–300 K. These results have indicated that, like the host material WS₂, the intercalated compounds also possess hexagonal symmetry and are diamagnetic p-type semiconductors. The activation energy for these compounds was determined from the conductivity data.     

Formation Process of FeCl<Subscript>3</Subscript>-NiCl<Subscript>2</Subscript>-Graphite Intercalation Compounds

The intercalation reaction of NiCl₂ from the mixture of FeCl₃ and NiCl₂ has been studied by using natural graphite at a wide range of residence times from 1 to 24 h. The microstructure changes of reaction products were investigated by XRD, SEM, and EDS, and the formation of ternary FeCl₃-NiCl₂-GICs was confirmed. In the process FeCl₃ was found to be intercalated preferentially at the initial stage of the intercalation, and set up the framework of the stage domain of GICs. Then NiCl₂ intercalated along the channels cut by FeCl₃. The diffusion rate and distribution uniformity of NiCl₂ controlled the rate of the intercalation reaction and the ternary grade of the FeCl₃-NiCl₂-GICs.     

Nickel-lithium oxide alloy transparent conducting films deposited by spray pyrolysis technique

In this research, nickel oxide (NiO) transparent semiconducting films are prepared by spray pyrolysis technique on glass substrates. The effect of Ni concentration in initial solution and substrate temperature on the structural, electrical, thermoelectrical, optical and photoconductivity properties of NiO thin films are studied. The results of investigations show that optimum Ni concentration and suitable substrate temperature for preparation of basic undoped NiO thin films with p-type conductivity and high optical transparency is 0.1 M and 450 °C, respectively. Then, by using these optimized deposition parameters, nickel-lithium oxide ((Li:Ni)O_x) alloy films are prepared. The XRD structural analysis indicate the formation of the cubic structure of NiO and (Li:Ni)O_x alloy films. Also, in high Li doping levels, Ni₂O₃ and NiCl₂ phases are observed. The electrical measurements show that the resistance of the films decreases with increasing Li level up to 50 at%. For these films, the optical band gap and carrier concentration are obtained to be 3.6 eV and 10¹⁵-10¹⁸ cm⁻³, respectively.     

Synthesis and magnetic properties of nickel nanoparticles deposited on the silicon nanowires

Nickel (Ni) nanoparticles with sizes of ∼35 nm were deposited on the surface of silicon nanowires (SiNWs) by electroless plating technique. The magnetic properties of Ni/SiNWs were investigated. The blocking temperature (T_B) of 370 K was obtained and confirmed by field-cooled (FC) and zero-field-cooled (ZFC) plots. The M-H hysteresis loops from 5 K to 400 K were measured. The saturation magnetization value was ∼4.5 emu/g and the coercivity was ∼375.3 Oe for the loop at 5 K, respectively. While for the loop at 400 K, these values were of ∼2.6 emu/g and ∼33.3 Oe, respectively. The temperature dependence of coercivity followed by the relation H_C(T) = H_C0[1 − (T/T_B)^1/2], indicating a superparamagnetic behavior. The magnetization of superparamagnetic grains in a magnetic field H was better described by Langevin function at 400 K. These novel magnetic properties of Ni/SiNWs were possibly attributed to the paramagnetic defects on the surface of SiNWs.     

Thermo-induced changes in EPR spectra of metal-free oligo- and polyphthalocyanines

Conjugated polymers (CP) are promising materials for various electronic, optical and magnetic applications, but clear understanding of their electron structure is not still achieved. Electron paramagnetic resonance (EPR) studies can give valuable information about electron states in polymers. We present a study of metal-free oligomeric (OPc) and polymeric (PPc) phthalocyanines by the EPR technique in the temperature interval from 300 to 500 K. Both of air-exposed and vacuum-processed samples have been investigated. The g-value, the intensity, the width and the shape of EPR signals observed in OPC and PPc at room temperature are typical of conjugated polymers. However, we found specificities of the EPR thermal behavior that was dependent on the oligomer molecular weight and sample's treatment. There was a certain temperature T₁ above which the EPR signal becomes time-dependent that reflects in a growing of the EPR signal intensity. We detected also another characteristic temperature T₂ (T₂ > T₁) above which the irreversible increasing of the EPR linewidth was observed. After vacuumization of OPc and PPc samples, the temperatures T₁ and T₂ shift to the higher values. The low-molecular OPc were characterized by the lesser value of T₂ in comparison with OPc of higher molecular masses and polymer samples. The computer analysis showed that the specific shape of the EPR line and its thermo-induced evolution can be explained by the coexistence of both localized and delocalized EPR-active centers.     

Structure and thermal behavior of multicomponent Fe68−xNixZr15Nb5B12 (x = 5, 10, 15, 20) alloys

Multicomponent Fe_68−xNi_xZr₁₅Nb₅B₁₂ (x = 5, 10, 15, 20) alloy powders milled for 60 h were prepared by mechanical alloying (MA). The structure and crystallization behavior were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). Ni enhances the amorphisation of alloy powders. Particle size increases with increasing Ni content. Both onset crystallization temperature T_x and the first crystallization peak temperature T_p of the four alloys shift to a higher temperature with increasing heating rate while melting temperature (T_m) is just the opposite. Fe_68−xNi_xZr₁₅Nb₅B₁₂ (x = 5, 10, 15, 20) alloys all have a large supercooled liquid region ΔT_x. The supercooled liquid region ΔT_x increases and the crystallization activation energy E decreases with increasing Ni content.     

Orientation of nitric acid molecules in graphite nitrate

A new model for HNO₃ intercalation into graphite is proposed. It was supposed that nitric acid forms double parallel layers between the graphit ic network. The new model is characterized by X-ray methods on the 00l line intensity. It is shown that the nitrate molecules are intercalated perpendicular to the graphite planes. The crystallographic stoichiometry gives C_4.3nHNO₃ for the n^th stage.     

The influence of Er substitution on magnetic and magnetocaloric properties of Dy1−xErxCo2 solid solutions

Magnetic and heat capacity measurements have been carried out on polycrystalline Dy_1?xEr_xCo₂ solid solutions (0 ≤ x ≤ 0.3). Powder X-ray diffraction at room temperature revealed that all Dy_1?xEr_xCo₂ solid solutions consist of the C15 cubic Laves phase MgCu₂ type structure. These solid solutions are ferromagnetic with a Curie temperature T_C below 138 K. Their Curie temperatures decrease from 138 K for DyCo₂ to 106 K for Dy_0.7Er_0.3Co₂. At higher temperatures, all solid solutions are Curie–Weiss paramagnets. Both magnetic and heat capacity measurements showed that all samples undergo a first-order type phase transition at T_C from paramagnetic to ferromagnetic state. Heat capacity measurements allowed us to determine the Debye temperature. The magnetocaloric effect has been estimated both in terms of isothermal magnetic entropy change and adiabatic temperature change in magnetic fields up to maximum 3 T.     

Electrical and mechanical properties of copper chloride-intercalated pitch-based carbon fibers

Using chlorine vapor transport we have intercalated pitch-based fibers, highly oriented pyrolytic graphite (HOPG), and natural single crystals of graphite with CuCl₂. In this paper we report mainly on the electrical properties of pitch-based fibers heat treated to 2500, 2750 and 3000 °C and then intercalated. The electrical resistivity both above and below room temperature, the tensile strength, and Young's modulus are reported. In very high magnetic fields at 4 K the fibers exhibit Shubnikov-de Haas oscillations, which means this powerful technique is now available as a diagnostic tool for intercalated fibers.     

Fe-Co-Ni-Cr-Mo-C-B-Y系大块金属玻璃的热稳定性、晶化行为、维氏硬度和磁性能

研究Fe41Co7-xNixCr15Mo14C15B6Y2(x=0,1,3,5)大块金属玻璃的热稳定性、晶化行为、维氏硬度和磁性能.通过铜模铸造法制备Fe41Co7-xNixCr15Mo14C15B6Y2(x=0,1,3,5)大块金属玻璃.利用差示扫描量热法和等温热处理法研究这些金属玻璃的热稳定性和晶化行为.在室温下利用维氏硬度计测量试样经过不同温度和时间退火后的硬度,并对它们的磁学性质进行表征.实验结果表明,少量Ni元素的加入没有增大过冷液相区间和玻璃形成能力,但是改变合金的初始晶化行为,增大晶化激活能.少量Ni元素的加入能够细化最终晶化组织中的晶粒大小.初晶相使合金的硬度降低,但随着热处理温度的升高,所有合金的硬度都明显提高,原因是析出了大量的碳化物和硼化物.退火温度对合金的磁性能有很大影响,少量Ni元素的加入阻止了合金在高温退火后从顺磁态向铁磁态的转变.     

Solid-state reactive diffusion between Ni and W

Various alloys are interconnected with W using a Ni intermediate layer by the diffusion bonding (DB) technique. During solid-state heating in the DB technique, however, reactive diffusion occurs at the interconnection between Ni and W. In order to examine the kinetics of the reactive diffusion, sandwich Ni/W/Ni diffusion couples were isothermally annealed at temperatures of T = 1023-1173 K for various times up to t = 366 h. Owing to annealing, Ni₄W is produced as a layer at the Ni/W interface in the diffusion couple and grows predominantly towards Ni. The thickness of the Ni₄W layer increases in proportion to a power function of the annealing time. The exponent of the power function is close to 0.5 at T = 1173 K and gradually decreases with decreasing annealing temperature. Furthermore, grain growth takes place in Ni₄W due to annealing. Therefore, volume diffusion is the rate-controlling process for the growth of Ni₄W at T = 1173 K. At T < 1173 K, however, boundary diffusion contributes to the rate-controlling process, and the contribution of boundary diffusion increases with decreasing annealing temperature. On the other hand, a region alloyed with W is formed in Ni from the Ni₄W/Ni interface by diffusion-induced recrystallization (DIR). The growth rate of the DIR region is much greater than the penetration rate of W into Ni by volume diffusion, and the concentration of W in the DIR region at the Ni₄W/Ni interface is equal to the solubility of W in Ni. Such growth behavior of the DIR region was numerically analyzed using a mathematical model. The analysis indicates that the growth of the DIR region is controlled by the interface reaction at the moving boundary of the DIR region as well as the boundary diffusion along the grain boundaries across the DIR region under the present annealing conditions.     

Pseudo-gap and the nonlinearity of the magnetization of textured polycrystals of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7 − <Emphasis Type="Italic">x</Emphasis></Subscript> above the temperature of transition into the superconducting state

Temperature dependences of the third and other higher harmonics of the magnetization of textured polycrystalline samples of YBa₂Cu₃O_{7 ? x} have been studied in the temperature range of 77–120 K. It has been revealed that the nonlinearity of magnetization of YBa₂Cu₃O_{7 ? x} is observed up to temperatures that considerably exceed the temperature of transition into the superconducting state. The observed nonlinearity of magnetization of YBa₂Cu₃O_{7 ? x} is ascribed to the appearance of a pseudogap state at T ～ 102 K in this compound. A method of determining the temperature of the appearance of the pseudogap T * in the high-T _c compounds is suggested, which is based on the measurement of magnetization harmonics.     

First-principles phase stability calculations and estimation of finite temperature effects on pseudo-binary Mg6(PdxNi1−x) compounds

The stability of pseudo-binary Mg₆(Pd_xNi_1?x) compounds has been studied at T = 0 K via first-principles calculations and at 673 K by thermodynamic modelling of finite temperature effects. At 0 K, these compounds are not stable since their formation energy is above the convex hull defined by the Mg, Mg₂Ni and Mg₆Pd phases, although the energy difference is not very high. However, at 673 K, vibrational and configurational entropic effects allow the stabilisation of some of the calculated pseudo-binary Mg₆(Pd_xNi_1?x) compounds. The vibrational contribution to the thermodynamic properties of the studied compounds has been calculated from Debye temperatures in the harmonic approximation. Also, the configurational entropy has been estimated taking into account the possible distribution of Pd and Ni between the several sites available in the pseudo-binary structure. The identification of intrinsic disorder and the associated energies and entropy are innovative features of this work. The phase diagram at the Mg-rich corner derived from these calculations is in fairly good agreement with recently published experimental results. In addition, the Ni for Pd substitution has been studied for the several sites available for Pd in the binary Mg₆Pd compound. The calculated preferential site occupancy is in agreement with the site occupancy factors determined in recent neutron diffraction experiments.     

Structure and electrical conductivity of graphite fibers prepared by pyrolysis of cyanoacetylene

Highly electroconductive graphite fibers are prepared by the pyrolysis (CVD) of cyanoacetylene on the surface of carbon fibers, followed by heat treatment. Many thin graphite strata, cylindrically layered and scrolled around an axial core of the original carbon fiber, are observed. The lattice constant C₀ of the graphite fiber obtained from cyanoacetylene and heat-treated at 3000 °C is 6.712° (002), which is smaller than that of a graphite fiber from benzene. The magnetoresistance of graphite fibers obtained from cyanoacetylene is as high as 800% (4.2K, 15 kG) (HTT 3300 °C), while that of graphite fibers obtained from benzene is around 150%. Measurements of Raman scattering and X-ray diffraction also show that cyanoacetylene forms more highly graphitized fiber than benzene. Cyanoacetylene is a good starting material for synthesizing graphite. The room temperature conductivity is as high as 1.8 × 10⁴ S/cm for fiber heat treated at 3250 °C. Treatment of the graphite fiber by fuming nitric acid increases the conductivity up to 1.3 sx 10⁵ S/cm in less than 10 min. Upon exposure of the nitrated fiber to air at ambient temperature, the conductivity decreases slightly. After this slight decrease, the conductivity is stable for at least 90 days.     

Magnetic and anomalous transport properties in Fe2MnAl

This study investigated the magnetism and anomalous transport properties of the melt-spun ribbon Fe₂MnAl alloy. It is found that the alloy exhibits ferromagnetic order with the Curie temperature of ∼150 K, followed by another magnetic transition at T_R ∼ 51 K. It is suggested there is antiferromagnetism pinning effect on the ferromagnetic matrix at the temperature below T_R. A steep rise of the resistance below T_R has been observed, which can be understood in terms of antiferromagnetic scattering. An appearance of the resistance maximum near the Curie temperature and the negative temperature dependence of the resistance above Curie temperature are associated with the magnetic phase transition from ferromagnetism to paramagnetism. A negative magnetoresistance at low temperature arising from inhomogeneous magnetic scattering is reported.     

Thermodynamics of La based La–Al–Cu–Ni–Co alloys studied by temperature modulated DSC

The onset and offset melting temperatures T_m and T_l, glass transition temperature T_g and heat of fusion ΔH_m of six La based La–Al–Cu–Ni–(Co) alloys were measured by DTA or DSC at a heating rate of 20 K/s. The absolute values of specific heat capacity for the undercooled liquid and the corresponding crystalline of these six alloys were obtained by means of temperature-modulated DSC (TMDSC). Entropy, enthalpy and Gibbs free energy differences between the undercooled liquid and crystalline of these alloys as a function of temperature have been calculated. Their glass forming ability was discussed from a thermodynamic point of view.     

Plasticity of indium antimonide between −176 and 400 °C under hydrostatic pressure. Part I: Macroscopic aspects of the deformation

Indium antimonide (InSb) single crystals have been plastically deformed between ?176 and 400 °C, i.e. below and above the brittle-to-ductile transition temperature situated around 150–160 °C, via the use of microindentation below room temperature (RT) and the Paterson press (compression under gaseous pressure) above RT. The evolution of the macroscopic mechanical data (hardness and critical resolved shear stress) with temperature suggests the existence of three deformation regimes with transitions at T_tr1 = 150 °C and T_tr2 = 20 °C. T_tr1 coincides with the brittle-to-ductile temperature, while T_tr2 may coincide with a transition in the nature of dislocations with dislocations propagating in the glide set above T_tr2 while moving in the shuffle set below T_tr2.     

Atomic scale calculation of the free volume in Zr2Ni metallic glass

How to evaluate the free volume in metallic glasses is a long-standing question in the field of metallic glasses. In this paper, a new approach at the atomic level to calculate free volume has been developed and applied in the Zr₂Ni metallic glass. The glass transition and volume change during the cooling of Zr₂Ni metallic liquid were investigated by molecular dynamics (MD). The MD resultant glass transition temperature (T_g) is about 700 K, which is close to the experimental value of 662.8 K obtained from differential scanning calorimetry (DSC). According to our method, the free volume in Zr₂Ni metallic glass was determined to be ～4.1% at T_g, which is comparable with the experimental results reported in other metallic glasses. Moreover, the probability distribution of free volume in our case can be fitted well by that given by Turnbull and Cohen, confirming the rationality of our method.     

Effect of alloying with Mn and Co on the temperature dependence of internal friction in Fe-Ni-C invar alloys

Temperature dependences of internal friction (TDIF) have been studied by the method of resonance bending vibrations in a kilohertz frequency range in the temperature range from 100 to 900 K in fcc Fe-Ni-X and Fe-Ni-X-C (X = Mn, Co) alloys with a Ni content of about 30 wt %. To produce a single-phase austenitic structure, the alloys were homogenized at 1373 K in vacuum and rapidly cooled in oil. At temperatures of 550–587 K, above the Curie temperature of the alloys, in the TDIF curves there is observed a carbon relaxation peak of internal friction. It has been demonstrated that in the alloys studied the temperature of the peak T _max at vibration frequencies of 1.5–2 kHz is more than 100 K higher than the Curie point T _C and that the alloying elements Mn and Co increase the difference between T _max and T _C. The activation energy calculated within the framework of the Wert-Marx model is equal to 1.1 eV. It has been found out that the alloying of Fe-Ni-C with Mn induces a certain decrease in the temperature and intensity of the carbon peak, while addition of Co, on the contrary, leads to an increase in the peak temperature and intensity of damhing of elastic vibrations. The causes of such effect have been considered.