Magnetic,electronic and thermodynamic properties of the heavy fermion compound CeNiAl4

We have carried out the magnetic susceptibility, electrical resistivity, specific heat, thermoelectric power and X-ray photoemission spectroscopy (XPS) measurements for CeNiAl₄. The magnetic susceptibilities have revealed a Curie–Weiss behavior above 30 K with a large negative paramagnetic Curie temperature θ_P = ?66 K and an effective moment of 2.45μ_B. The f-occupancy and the coupling between the f level and the conduction states are derived from XPS to be about 0.83 and ～40–64 meV, respectively. The valence state of the Ce ion is close to 3+. Extrapolation of the lowest temperatures range of C/T(T²) yields the electronic specific heat coefficient γ = 0.5 J mol^?1 K^?2. In combination with the thermoelectric power and resistivity data, a heavy fermion state is confirmed in CeNiAl₄.     

Solidification behavior of γ′-Ni3Al-containing alloys in the Ni–Al–O system

The chemical activities of Al and Ni in γ′-Ni₃Al-containing alloys were measured using the multi-cell Knudsen effusion-cell mass spectrometry technique, over the composition range 8–32 at.% Al and temperature range T = 1400 to 1750 K. From these measurements a better understanding of the equilibrium solidification behavior of γ′-Ni₃Al-containing alloys in the Ni–Al–O system was established. Specifically, these measurements revealed that (i) γ′-Ni₃Al forms via the peritectiod reaction, γ + β (+Al₂O₃) = γ′ (+Al₂O₃), at 1633 ± 1 K; (ii) the {γ + β + Al₂O₃} phase field is stable over the temperature range 1633–1640 K; and (iii) equilibrium solidification occurs by the eutectic reaction, L (+Al₂O₃) = γ + β (+Al₂O₃), at 1640 ± 1 K and a liquid composition of 24.8 ± 0.2 at.% Al (at an unknown oxygen content). When projected onto the Ni–Al binary, this behavior is inconsistent with the current Ni–Al phase diagram and a new diagram is proposed. This new Ni–Al phase diagram explains a number of unusual steady-state solidification structures reported previously and provides a much simpler reaction scheme in the vicinity of the γ′-Ni₃Al phase field.     

Crystal structure and physical properties of a magnetic molecular conductor (EDO-TTFVODS)2FeCl4

Crystal structure, and electrical conducting and magnetic properties of a radical cation salt of EDO-TTFVODS with magnetic FeCl₄^? ion, (EDO-TTFVODS)₂FeCl₄ (EDO-TTFVODS = ethylenedioxytetrathiafulvalenoquinone-1,3-diselenolemethide) are reported. In this salt, there are two independent donor molecules formed two different layers A and B, and the counter FeCl₄^? ions layer is sandwiched between two donor layers A and B along the b-axis. The donor molecules form the one-dimensional columns along the a-axis in both donor layers. This salt shows high conductivity at room temperature (σ_RT = 25 S cm^?1) and a metallic behavior down to ca. 80 K, where a metal–insulator transition however occurs. The magnetic susceptibility obeys a Curie–Weiss law (Curie constant C = 4.42 emu K mol^?1 and Weiss temperature Θ = ?1.5 K), without any magnetic ordering down to 1.8 K. This result suggests the weak antiferromagnetic interaction between the d spins of FeCl₄^? ions.     

Reactively sputtered epitaxial γ′-Fe4N films: Surface morphology,microstructure, magnetic and electrical transport properties

Epitaxial γ′-Fe₄N films with (1 0 0) and (1 1 0) orientations have been fabricated by reactive sputtering; these films were characterized by X-ray θ–2θ and φ scans, pole figures and high-resolution transmission electron microscopy. The film surface is very smooth as the film is less than 58 nm thick. The films exhibit soft ferromagnetism, and the saturation magnetization decreases with an increase in temperature, following Bloch’s spin wave theory. The films also exhibit a metallic conductance mechanism. Below 30 K, magnetoresistance (MR) is positive and increases linearly with the applied field in the high-field range. In the low-field range, MR increases abruptly. Above 30 K, MR is negative, and its value increases linearly with the applied field.     

Controlling of silicon–insulator–metal junction by organic semiconductor polymer thin film

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO₂/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 10⁵ at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the I–V characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO₂/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V_oc) along with a short circuit current (I_sc). This suggests that the n-Si/SiO₂/MEH-PPV/Al diode is a photovoltaic device with V_oc = 0.456 V and J_sc = 7.89 × 10^?8 A/cm² values under 100 mW/cm² illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D_it values with time constant τ_it of the diode under dark and illumination conditions were found to be 2.53 × 10¹⁰ eV^?1 cm^?2 with 5.09 × 10^?5 s and 2.50 × 10¹⁰ eV^?1 cm^?2 with 8.27 × 10^?5 s, respectively. The obtained results indicate that the n-Si/SiO₂/MEH-PPV/Al diode is a photo-sensitive diode.     

High-field magnetization and specific heat of UCu2T3Al7 alloys where T = Cr,Mn and Fe(II)

The UCu₂T₃Al₇ alloys, where T = Cr, Mn and Fe, crystallize in the ThMn₁₂-type tetragonal structure. Earlier investigation of magnetic and electrical properties revealed their complex magnetic behavior except of the Cr compound, which is paramagnetic, whereas their electrical resistivity is weakly temperature dependent. At present we report on the magnetization measurements at 4.2 and 77 K in the steady magnetic field up to 14 T and in the pulsed field up to 34 T with a pulse duration of 10 ms at T = 4.2 K. These experiments confirmed paramagnetism of the Cr alloy and showed lack of saturation for the compounds of the Mn and Fe with the “saturation” magnetic moment amounting to 3.1 and 5.0 μ_B/f.u., respectively. In turn, the specific heat was measured in the temperature range 1.2–70 K in magnetic field μ₀H = 0 and 7 K using a home-made and fully automatic calorimeter. The investigation of the specific heat at temperature 2–300 K has been done using Quantum Design PPMS machine. The magnetic field does not in principle influence the obtained results, whereas the coefficient of the electronic specific heat, γ is strongly enhanced and amounts to 410, 330 and 150 mJ mol^?1 K^?2 for the Cr, Mn and Fe compounds, respectively.     

Structural and mechanical properties of Cr–Al–O–N thin films grown by cathodic arc deposition

Coatings of (Cr_xAl_1?x)_δ(O_1?yN_y)_ξ with 0.33 ? x ? 0.96, 0 ? y ? 1 and 0.63 ? δ/ξ ? 1.30 were deposited using cathodic arc evaporation in N₂/O₂ reactive gas mixtures on 50 V negatively biased WC–10 wt.% Co substrates from different Cr and Al alloys with three different Cr/Al compositional ratios. For N₂ < 63% of the total gas, ternary (Cr,Al)₂O₃ films containing <1 at.% of N forms; as determined by elastic recoil detection analysis. Increasing the N₂ fraction to 75% and above results in formation of quaternary oxynitride films. Phase analyses of the films by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy show the predominance of cubic Cr–Al–N and cubic-(Cr,Al)₂O₃ solid solutions and secondary hexagonal α-(Cr,Al)₂O₃ solid solution. High Cr and Al contents result in films with higher roughness, while high N and O contents result in smoother surfaces. Nanoindentation hardness measurements showed that Al-rich oxide or nitride films have hardness values of 24–28 GPa, whereas the oxynitride films have a hardness of ～30 GPa, regardless of the Cr and Al contents. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.     

Crystal structure and properties of U2Co3Al9

A new ternary compound with stoichiometry U₂Co₃Al₉ has been synthesized. It adopts the orthorhombic Y₂Co₃Ga₉-type structure (space group Cmcm, Z = 4, a = 12.824(2) Å, b = 7.515(1) Å, c = 9.249(2) Å). Measurements of dc- and ac-magnetic susceptibility, electrical resistivity, and magnetoresistivity on polycrystalline samples have been performed. The Curie–Weiss law is strictly followed, with θ_CW = −48 K and μ_eff = 3.2 μ_B. A small kink observed in the temperature dependence of the resistivity is attributed to a phase transition at T_t = 8 K. The magnetoresistivity was found to be negative at all temperatures examined below 45 K, with a sharp minimum at T_t = 8 K.     

Extraction of electronic parameters of organic diode fabricated with NIR absorbing functional manganase phthalocyanine organic semiconductor

The semiconducting and metal/organic semiconductor properties of the newly synthesized NIR absorbing α-substituted manganase phthalocyanine bearing functional 2,3-dihydroxypropylthio moieties {M[Pc(S–CH₃CH₂(OH)CH₂(OH))]₄X}(M = Mn^III) have been investigated by electrical conductivity–temperature, optical absorption and current–voltage characteristics methods. The electrical conductivity increases with the temperature, suggesting that the peripheral α-substituted-functional manganase phthalocyanine is an organic semiconductor. The optical band gap and trap energy values were determined and were found to be 2.98 eV and 1.95 eV, respectively. The ITO/MnPc/Al diode shows a rectifying behavior due to the formation of MnPc/Al interface with a rectification ratio of 29.4 at ±2 V. The series resistance R_s and ideality factor n values were found to be 102.6 kΩ and 8.89, respectively. The interface state density for the diode was of order of 2.73 × 10¹¹ eV^?1 cm^?2 with the interface time constant of 1.93 × 10^?5.It is evaluated that newly synthesized α-substituted manganase phthalocyanine bearing functional 2,3-dihydroxypropylthio moieties is an organic semiconductor and can be used in electronic device applications as an organic diode.     

Wetting of porous titanium carbonitride by Al–Mg–Si alloys

Wetting of porous TiC_0.17N_0.83 by six alloys from the Al–Mg–Si system (pure Al, pure Mg, Al–15 at.% Mg, Al–10 at.% Si, Mg–5 at.% Si, and Al–10 at.% Mg–10 at.% Si) in an argon atmosphere was studied using the sessile drop experiment. The contact angle of the liquid drops on TiC_0.17N_0.83 substrates was measured as a function of temperature. Aluminium, Al–10 at.% Si, and Al–10 at.% Mg–10 at.% Si did not wet TiC_0.17N_0.83 in the studied temperature range. Magnesium always wetted TiC_0.17N_0.83 with a minimum contact angle of ≈44° at 900°C, and alloying with Mg significantly lowered the contact angle of Al on TiCN. Alloying with Si deteriorated the wetting of TiCN by Mg. A comparative study between the systems was conducted, based on the results and on data available in the literature. The improvement of the wetting of TiCN by Al due to alloying with Mg can be explained by the segregation of Mg to the interface with TiCN, where it lowers the interface energy. The addition of Si to pure Mg or to Al–Mg results in an increase in the contact angle on TiCN.     

Proximity effect controlled superconducting behavior of novel biphasic Pb–Sn nanoparticles embedded in an Al matrix

We report the synthesis of biphasic Pb (46 at.%)–Sn (54 at.%) nanoparticles dispersed in an aluminum matrix and explore the nature of the superconducting transition in these particles. The nanoscaled Pb–Sn alloy particles were dispersed in Al by rapid solidification and the two-phase nature of these particles was characterized by transmission electron imaging, diffraction and composition mapping. A weak superconducting transition occurs at 3.1 K in these alloys, which is much lower than the T_C expected for a Pb₄₆Sn₅₄ alloy or that due to the proximity effect between Pb and Sn. We show that it is the superconducting Al matrix with T_C = 1.2 K that plays a major role in determining the effective transition temperature of the system.     

Structural and mechanical properties of corundum and cubic (AlxCr1−x)2+yO3−y coatings grown by reactive cathodic arc evaporation in as-deposited and annealed states

Coatings of (Al_xCr_1?x)_2+yO_3?y with 0.51 ? x ? 0.84 and 0.1 ? y ? 0.5 were deposited on hard cemented carbide substrates in an industrial cathodic arc evaporation system from powder-metallurgy-prepared Cr/Al targets in pure O₂ and O₂ + N₂ atmospheres. The substrate temperature and bias in all the deposition runs were 575 °C and ?120 V, respectively. The composition of the coatings measured by energy dispersive X-ray spectroscopy and elastic recoil detection analysis differed from that of the facing targets by up to 11%. Microstructure analyses performed by symmetrical X-ray diffraction and transmission electron microscopy showed that corundum, cubic or mixed-phase coatings formed, depending on the Cr/Al ratio of the coatings and O₂ flow per active target during deposition. The corundum phase was promoted by high Cr content and high O₂ flow per target, while the cubic phase was observed mostly for high Al content and low O₂ flow per active target. In-situ annealing of the cubic coatings resulted in phase transformation from cubic to corundum, completed in the temperature range of 900–1100 °C, while corundum coatings retained their structure in the same range of annealing temperatures. Nanoindentation hardness of the coatings with Cr/Al ratio <0.4 was 26–28 GPa, regardless of the structure. Increasing the Cr content of the coatings resulted in increased hardness of 28–30 GPa for corundum coatings. Wear resistance testing in a turning operation showed that coatings of Al–Cr–O have improved resistance to crater wear at the cost of flank wear compared with TiAlN coatings.     

Preparation of dense TiN1 − X (X = 0–0.4) by pulsed electric current sintering: Densification and mechanical behavior

Bulks of TiN_1 − X in the range of X = 0–0.4 with high density were prepared by a new method which comprises the reaction between TiN with TiH₂ through pulsed electric current sintering. X-ray diffractograms revealed that single fcc phase with nitrogen vacancies was achieved after sintering; further observation by scanning electron microscopy showed homogeneous structure in all samples and larger grain size by increasing the amount of TiH₂. The maximum Vickers hardness measured on the samples was approximately 31 GPa at X = 0.3. An increase in hardness was observed in non-stoichiometric samples even its larger grain size. The grain size-indent diagonal ratio was calculated from 1.2 at X = 0 to 5.6 at X = 0.4. The addition of TiH₂ showed an improvement in both densification and hardness without significant degradation of fracture toughness. Based on these results, the mechanical properties of TiN_1 − X bulks can be controlled as a function of TiH₂/TiN ratios in order to be used for different applications.     

An investigation of the Al–Pd–Rh phase diagram between 50 and 100 at% Al

Partial 1100, 1000, 900 and 790 °C isothermal sections of the Al–Pd–Rh phase diagram were studied. The isostructural binary AlPd and AlRh phases probably form a continuous β-range of the CsCl-type solid solutions. The Al–Pd and Al–Rh ε-phases form another continuous range. The C–Al₅Rh₂ phase dissolves up to 13 at% Pd, Al₉Rh₂ and Al₇Rh₃ are extended up to 3 at% Pd. Two ternary phases: cubic C₂ (a=1.5483 nm) and hexagonal C₃ (a=1.09159, c=1.3386 nm) were revealed. The former extends along about 65 at% Al from 4 to 27 at% Pd.     

Effect of growth rate on microstructure and mechanical properties of directionally solidified multiphase intermetallic Ni–Al–Cr–Ta–Mo–Zr alloy

The effect of growth rate on microstructure and mechanical properties of directionally solidified (DS) multiphase intermetallic alloy with the chemical composition Ni–21.9Al–8.1Cr–4.2Ta–0.9Mo–0.3Zr (at.%) was studied. The DS ingots were prepared at constant growth rates V ranging from 5.56 × 10⁻⁶ to 1.18 × 10⁻⁴ ms⁻¹ and at a constant temperature gradient at the solid–liquid interface of G_L = 12 × 10³ K m⁻¹. Increasing growth rate increases volume fraction of dendrites and decreases primary dendritic arm spacing, mean diameter of α-Cr (Cr-based solid solution) and γ′(Ni₃Al) precipitates within the dendrites. Room-temperature compressive yield strength, ultimate compressive strength, hardness and microhardness of dendrites increase with increasing growth rate. All room-temperature tensile specimens show brittle fracture without yielding. The brittle-to-ductile transition temperature for tensile specimens is determined to be about 1148 K. Minimum creep rate is found to depend strongly on the applied stress and temperature according to the power law with a stress exponent of n = 7 and apparent activation energy for creep of Q_a = 401 kJ/mol.     

The characterization of structure,thermal stability and magnetic properties of Fe–Co–B–Si–Nb bulk amorphous and nanocrystalline alloys

Recently bulk amorphous alloys have attracted great attention due to their excellent magnetic properties. The glass-forming ability of bulk amorphous alloys depends on the temperature difference (ΔT_x) between glass transition temperature (T_g) and crystallization temperature (T_x). The increase of ΔT_x causes a decrease of the critical cooling rate (V_c) and growth of the maximum casting thickness of bulk amorphous alloys. The aim of the present paper is to characterize the structure, the thermal stability and magnetic properties of Fe₃₆Co₃₆B₁₉Si₅Nb₄ bulk amorphous alloys using XRD, Mössbauer spectroscopy, DSC and VSM methods. Additionally the magnetic permeability μ_i (at force H ≈ 0.5 A/m and frequency f ≈ 1 kHz) and the intensity of disaccommodation of magnetic permeability Δμ/μ(t₁) (Δμ = μ(t₁ = 30 s) ? μ(t₂ = 1800 s)), have been measured, where μ is the initial magnetic permeability measured at time t after demagnetisation, the Curie temperature T_C and coercive force H_c of rods are also determined with the use of a magnetic balance and coercivemeter, respectively.Fe–Co–B–Si–Nb bulk amorphous alloys were produced by pressure die casting with the maximum diameters of 1 mm, 2 mm and 3 mm.The glass transition temperature (T_g) of studied amorphous alloys increases from 807 K for a rod with a diameter of 1 mm to 811 K concerning a sample with a diameter of 3 mm. The crystallization temperature (T_x) has the value of 838 K and 839 K for rods with the diameters of 1 mm and 3 mm, respectively. The supercooled liquid region (ΔT_x = T_x ? T_g) has the value of about 30 K. These values are presumed to be the origin for the achievement of a good glass-forming ability of the Fe–Co–B–Si–Nb bulk amorphous alloy. The investigated amorphous alloys in the form of rods have good soft magnetic properties (e.g. M_s = 1.18–1.24 T). The changes of crystallization temperatures and magnetic properties as a function of the diameter of the rods (time of solidification) have been stated.     

Crystal structures and magnetic properties of two molecular solids based on bis(maleonitriledithiolate)nickelate monoanion with substituted piperidinium cations

Two new molecular solids, [1-NaMePid][Ni(mnt)₂] (1) and [2-NaMePid][Ni(mnt)₂] (2) (mnt^2? = maleonitriledithiolate, [1-NaMePid]⁺ = 1-(1′-naphthylmethyl)piperidinium and [2-NaMePid]⁺ = 1-(2′-naphthylmethyl)piperidinium) have been characterized structurally and magnetically. Both [Ni(mnt)₂]^? anions and the cations of 1 and 2 form segregated column stacks, and the Ni(III) ions form a 1D zigzig alternating magnetic chain within a [Ni(mnt)₂]^? column through Ni···S, S···S, Ni···Ni, or π···π interactions. Some conformational features in two isomeric cations and the geometry of the individual [Ni(mnt)₂]^? anion for 1 and 2 remain similar, while the changes of the space filling properties, the packing requirements and the existence of the water molecule in 2 result in the difference of the stacking mode of the [Ni(mnt)₂]^? anions. Magnetic susceptibility measurements in the temperature range 2–300 K show that 1 is diamagnetism, while 2 exhibits a novel and interesting spin–gap transition around 16.8 K with antiferromagnetic interaction (J = ?4.6 cm^?1) in the high-temperature phase (HT) and the spin–gap (Δ/k_b = 68.5 K) in the low-temperature phase (LT).     

Phase formation and thermal stability in Cu–Zr–Ti(Al) metallic glasses

In the present study we investigate the phase formation and the thermal stability of Cu₅₀Zr_50 ? xTi_x (0 ≤ x ≤ 10) and (Cu_0.5Zr_0.5)_100 ? xAl_x glass-forming alloys. Parameters indicating the glass-forming ability (GFA) are calculated from isochronal and isothermal calorimetric experiments. A high Ti content in the Cu–Zr–Ti alloys causes the precipitation of a metastable ternary Laves phase (C15), which does not form in Cu–Zr–Al. Accompanied with it is a significant drop in the activation energy of crystallization. Also the supercooled liquid region (ΔT_x = T_x ? T_g), the reduced glass transition temperature (T_rg = T_g/T_liq), and the γ parameter (γ = T_x/(T_g + T_liq)) (T_x: crystallization temperature, T_g: glass transition temperature and T_liq: liquidus temperature) are sensitive to the change in the crystallization sequence. The fragility values calculated are believed to overestimate the GFA of the investigated alloys. Careful selection of the alloy composition enables the targeted precipitation of different crystalline phases.     

Experimental and computational study on the effect of yttrium on the phase stability of sputtered Cr–Al–Y–N hard coatings

The effect of Y incorporation into cubic Cr–Al–N (B1) was studied using ab initio calculations, X-ray diffraction and energy-dispersive X-ray analysis of sputtered quaternary nitride films. The data obtained indicate that the Y incorporation shifts the critical Al content, where the hexagonal (B4) structure is stable, to lower values. The calculated critical Al contents of x ≈ 0.75 for Cr_1?xAl_xN and x ≈ 0.625 for Cr_1?x?yAl_xY_yN with y = 0.125 are consistent with experimentally obtained values of x = 0.69 for Cr_1?xAl_xN and x = 0.68 and 0.61 for Cr_1?x?yAl_xY_yN with y = 0.02 and 0.06, respectively. This may be understood based on the electronic structure. Both Cr and Al can randomly be substituted by Y. The substitution of Cr by Y increases the phase stability due to depletion of non-bonding (anti-bonding) states, while the substitution of Al by Y decreases the phase stability mainly due to lattice strain.     

Microstructure and mechanical properties of MoSi2/TaSi2 two-phase alloys

Effects of pre-strain on the compressive mechanical behavior were investigated on the alloys with an aligned lamellar microstructure consisting of C11_b MoSi₂ and C40 TaSi₂ prepared through optical floating zone (OFZ) method and annealing in the two-phase MoSi₂/TaSi₂ region. Single crystals of C40 TaSi₂ were successfully grown at solidification rate of 5 or 10 mm/h, and well-aligned lamellar microstructure can be achieved by selecting an MoSi₂–17 mol% TaSi₂ alloy. Firstly, compression tests were conducted to examine the effect of the angle ϕ between the aligned lamellae and the loading axis on strength and ductility. Results indicate that ϕ = 0, lamellae parallel to the axis, is a hard-orientation and ϕ = 54 and 40 (identically 45) are soft orientations. The alloy with ϕ = 0 shows higher strength but lower ductility than those with ϕ = 54 and 40 where ductility is evaluated in terms of brittle-to-ductile transition temperature (BDTT). Then effects of pre-straining at 1773 K on the mechanical behavior at 1573 K were investigated using soft-oriented lamellar alloys with ϕ = 40 whose BDTT is determined at least lower than 1673 K. Pre-straining to a few to several percent at 1773 K improves ductility of the alloy at 1573 K and also raises 0.2% flow stress, compared with the absence of the pre-strain. We believe that dislocations can be generated and stored in the alloy at 1773 K, and these dislocations are mobile even at 1573 K, although the analyses of operative slip systems and characteristics of dislocations remain as future works.