Spectroscopic investigations of the BEDT-TTF charge transfer salts with NO3− anions (β″- and δ-phase)

We report the polarized reflectance spectra (650–6500 cm⁻¹) as well FT-NIR Raman spectra of β″-(BEDT-TTF)₃(NO₃)₂ and δ-(BEDT-TTF)₂(NO₃)_0.9(NO₂)_0.1 salts as a function of temperature. Additionally, the crystal structure of δ-phase salt was determined at room temperature and the temperature dependence of electrical conductivity was measured. The reflectance spectra of metallic β″-phase salt were fitted with the Drude model; the metal–insulator transition at T = 20–27 K has practically no influence on IR spectra. The δ-phase salt shows semiconducting behavior; inside conducting organic layers the BEDT-TTF molecules are arranged in dimers. The specific vibrational features of the δ-salt are discussed in terms of hydrogen bonding between BEDT-TTF and anions.     

Isothermal section of the Er–Fe–Al ternary system at 800 °C

Physico-chemical analysis techniques, including X-ray diffraction and Scanning Electron Microscope–Energy Dispersive X-ray Spectroscopy, were employed to construct the isothermal section of the Er–Fe–Al system at 800 °C. At this temperature, the phase diagram is characterized by the formation of five intermediate phases, ErFe_12?xAl_x with 5 ≤ x ≤ 8 (ThMn₁₂-type), ErFe_1+xAl_1?x with ?0.2 ≤ x ≤ 0.75 (MgZn₂-type), ErFe_3?xAl_x with 0.5 < x ≤ 1 (DyFe₂Al-type), Er₂Fe_17?xAl_x with 4.74 ≤ x ≤ 5.7 (TbCu₇-type) and Er₂Fe_17?xAl_x with 5.7 < x ≤ 9.5 (Th₂Zn₁₇-type), seven extensions of binaries into the ternary system; ErFe_xAl_3?x with x < 0.5 (Au₃Cu-type), ErFe_xAl_2?x with x ≤ 0.68 (MgCu₂-type), Er₂Fe_xAl_1?x with x ≤ 0.25 (Co₂Si-type), ErFe_2?xAl_x with x ≤ 0.5 (MgCu₂-type), ErFe_3?xAl_x with x ≤ 0.5 (Be₃Nb-type), Er₆Fe_23?xAl_x with x ≤ 8 (Th₆Mn₂₃-type), and Er₂Fe_17?xAl_x with x ≤ 4.75 (Th₂Ni₁₇-type) and one intermetallic compound; the ErFe₂Al₁₀ (YbFe₂Al₁₀-type).     

A study on mechanochemical behavior of MoO3–Mg–C to synthesize molybdenum carbide

The influence of Mg value in the MoO₃–Mg–C mixture on the molybdenum carbide formation and the mechanism of reactions during mechanochemical process were investigated. In keeping with this aim, magnesium and carbon contents of the mixture were changed according to the following reaction: 2MoO₃ + (6 − x) Mg + (1 + x) C = (6 − x) MgO + Mo₂C + x CO. The value of x varied from 0 to 6. Differential thermal analysis (DTA) results for sample with stoichiometric ratio (x = 0) revealed that in the early stage, carbon reduced the MoO₃ to MoO₂ and subsequently highly exothermic magnesiothermic MoO₂ reduction occurred after magnesium melting. Also, it was indicated that the exothermic reaction temperature shifted to before magnesium melting in the 11 h-milled sample (x = 0) and all the exothermic reactions happened, simultaneously. According to the experimental findings, molybdenum carbide (Mo₂C) was synthesized in the mixture powder with stoichiometric ratio (x = 0) after 12 h milling process and the type of reactions was mechanically induced self-sustaining reaction (MSR). However, at lower Mg content in the MoO₃–Mg–C mixture (0 < x ≤ 2), the magnesiothermic reduction occurred in MSR mode and activated the carbothermal reaction. Further decrease in Mg value (2 < x ≤ 3) resulted in MSR mode magnesiothermic reaction and gradual carbothermal reduction. In samples with lower magnesium contents, partial molybdenum oxide reduction proceeded through a gradual mode magnesiothermic reaction.     

Structural properties and magnetic behavior in CoFe1−xAlx alloys

Structural properties and magnetic behavior in CoFe_1−xAl_x ternary alloys are studied as functions of composition (0≤x≤1) and quenching temperature (773–1273 K). The B2-phase exists stably over wide ranges of composition and temperature and the Heusler (L2₁)-phase appears around the stoichiometric composition (0.4≤x≤0.6) below about 973 K. In the B2-phase region, the mean magnetic moment decreases nearly linearly with increase in x. Furthermore, the moment decreases with increase in quenching temperature in x<0.4, while it remains almost constant in x≥0.4. In the Heusler-phase region, the mean magnetic moment has nearly the same value as that in the B2-phase, and shows no remarkable quenching temperature dependence. The correlation between the magnetic behavior observed in both phases and the point defect properties is discussed in terms of the long-range order (LRO) parameters.     

Phase stability,mechanical property,and electronic structure of Mg–Li system

First principle calculation reveals that the HCP, BCC, and FCC Mg_100?xLi_x phases are energetically favorable with negative heats of formation, and are predicted to be the most stable structures at 0 K when 0 ≤ x < 18, 18 ≤ x < 73, and 73 ≤ x ≤ 100, respectively. Calculation also shows that for Mg–Li phases there is an almost linear variation of bulk moduli with composition, and crystal structure has only a little effect on bulk moduli. In addition, it is found that Mg₃Li and MgLi have phase sequences of BCC → HCP → FCC and BCC → FCC under high pressure, respectively, and that the anomalous mechanical instability of the HCP MgLi phase would be attributed to its weak bonding and step-like electronic structure of valence bands.     

Phase stabilization in the Fe1−xMnxSi2 system induced by ball milling

Phase formation in the Mn doped iron disilicide system Fe_1−xMn_xSi₂ with 0.00 ≤ x ≤ 0.24 was studied using X-ray diffraction and Mössbauer spectroscopy. Samples were prepared at room temperature in Ar atmosphere by two different routes. The first one involved the simultaneous mill of the pure elements, and the second one the milling in two steps, first the premixture of metals and then the addition of Si. Both routes produced β-FeSi₂, ɛ-FeSi and α-FeSi₂ phases. In the first case, the segregation of MnSi and Si was also observed. The diffraction results and the obtained set of hyperfine parameters supported the coexistence of β-FeSi₂, α-FeSi₂ and ɛ-FeSi. The relative phase composition depended on the preparation route, being the obtained fraction of the ɛ-FeSi smaller when the second preparation route was followed. It seemed that the previous formation of a Fe_1−xMn_x alloy before to the silicide overcomes the chemical driving forces.     

Microstructure and mechanical properties of Laves phase-reinforced Fe–Zr–Cr alloys

Multi-phase Fe_90?xZr₁₀Cr_x alloys with 0 ≤ x ≤ 10 containing cubic C15 and hexagonal C14/C36 Laves phases have been prepared by copper mold casting. The microstructure of the samples consists of micrometer-sized Laves phase particles embedded in an ultrafine eutectic matrix of alternating lamellae of α-Fe and Laves phases. Room temperature compression tests of the binary alloy reveal a high strength of 1900 MPa combined with a plastic strain of about 9%. The addition of Cr improves the plastic strain up to 17% while reducing the strength only by about 70 MPa. The increased plastic deformation is linked to the specific structural features of the Laves phases. For the binary alloy, shearing and crack formation within the C15 phase limits plastic deformation. In contrast, in the samples containing Cr no shearing occurs within the C14/C36 phases and crack formation, which is observed at the particle/ferrite interface, is retarded.     

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.     

Properties of nanocrystalline and nanocomposite WxZr1−x thin films deposited by co-sputtering

W_xZr_1?x thin films were deposited at room temperature on glass substrates by co-sputtering tungsten and zirconium targets in argon. The composition was found in the range 0 ≤ x ≤ 0.81. The grain size deduced from X-ray diffraction analysis ranged from 1.3 nm to 16 nm depending on the composition. The events in the resistivity, optical reflectivity and thickness evolutions were correlated with the X-ray diffraction analysis. Depending on the composition, the local organization can be attributed to a nanocrystalline solid solution of W in Zr, to a nanocomposite structure involving ZrW₂ nanograins embedded in an amorphous matrix, to ZrW₂ Laves phase nanograins and to a nanocrystalline solid solution of Zr in W. For 0 < x ≤ 0.72, the equivalent grain size is very small (less than 2 nm) and the evolution of the resistivity can be fitted by the estimated volume of the material perturbed by the grain boundaries.     

Limits of the Mg–Al γ-phase range by ball-milling

In the present work, the homogeneity range of the Mg–Al γ-phase was studied by ball-milling with post-annealing. In order to estimate the limit of its domain range, several Mg_XAl_100−X compounds from X = 47.5 to 70 by incremental steps of 2.5 were prepared. Different experimental measurements (XRD, SEM, EDX, DSC) were performed and are in mutual agreement with the properties of the existing phases. They show that deviation from the ideal composition of the intermetallic Mg₁₇Al₁₂ structure (X = 58.62) leads to a decrease of the homogeneity (morphological and chemical compositions). Rietveld refinements on XRD patterns show that the single γ-phase range is extended at room temperature and is identified for 55 ≤ X ≤ 62.5 at.% of nominal Mg powder.     

Formation of bulk metallic glasses in Cu45Zr48−xAl7REx (RE = La,Ce, Nd,Gd and 0 ≤ x ≤ 5 at.%)

We report a series of bulk metallic glass-forming alloys of compositions (Cu₄₅Zr_48−xAl₇RE_x, RE = La, Ce, Nd, Gd and 0 ≤ x ≤ 5 at.%). By using a conventional copper mold sucking method, alloys with diameters ranging from 5 to 10 mm can be readily solidified into an amorphous structure without detectable crystallites. The best glass-forming ability is obtained for the alloys Cu₄₅Zr₄₆Al₇RE₂. Possible effects of RE addition on the glass-forming ability are discussed. In addition, the compositional effect on mechanical properties of Zr–Cu–Al–Gd alloys is presented.     

Ni–(Zr/Hf)–(Nb/Ta)–Al bulk metallic glasses with high thermal stabilities

Thermal stability is a critical consideration in the application of metallic glasses as hydrogen separation material. The development of new Ni-based bulk metallic glasses (BMGs) with enhanced thermal stability is desirable. The present work investigated the alloying effects of refractory metals Hf and Ta on the Ni₆₀Zr₂₀Nb₁₅Al₅ bulk metallic glass. Two serial alloys, namely, Ni₆₀Zr_20 ? xHf_xNb₁₅Al₅ (x = 0～20 at.%) and Ni₆₀Zr₂₀Ta_yNb_15 ? yAl₅ (y = 0～15 at.%), were investigated in the present work. The addition of Hf or Ta was revealed to be effective in improving the thermal stability of the basic alloy, while the glass-forming ability of the alloy is slightly reduced resulting from the addition of Hf or Ta. The possible mechanism of these alloying effects is discussed.     

High-temperature oxidation behavior of minor Hf doped NiAl alloy in dry and humid atmospheres

Oxidation behavior of NiAl and 0.05 at.% Hf doped NiAl alloys were investigated at 1100 °C in dry and humid atmospheres. Hf doping significantly improved the cyclic oxidation resistance. Water vapour promoted the formation of voids at the scale/alloy interface and accelerated scale spallation. Also, water vapour had effect on the phase transformation from θ- to α-Al₂O₃ at the initial oxidation stage. In humid atmosphere, more Hf segregated at the scale/alloy interface to form oxide pegs. Pre-oxidation process in O₂ + Ar could compromise the effect of humid atmosphere on the oxidation kinetics of the NiAl alloys.     

Phase equilibria in the Ni-rich portion of the Ni–Ga binary system

The phase equilibria in the composition range from 0 to 60 at% Ga of the Ni–Ga system were determined by electron probe microanalysis (EPMA) using diffusion couples, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). It was found that while the phase equilibria between the α′ (L1₂: Ni₃Ga) and α (Ni-solid solution) or β (B2: NiGa) phases are basically in agreement with the diagram evaluated by Lee and Nash, those between γ (B8₁: Ni₁₃Ga₇), δ (Cmmm: Ni₅Ga₃) and ɛ (C2/m: Ni₁₃Ga₉) are topologically different from that diagram. Three eutectoid reactions (γ → δ + ɛ, β → γ + ɛ, β → α′ + γ) and one peritectoid reaction (α′ + γ → δ) were confirmed and the temperatures and concentrations of those invariant reactions were determined.     

Synthesis of high purity titanium silicon carbide from elemental powders using arc melting method

The objective of this study is to investigate the formation of Ti₃SiC₂ from Ti/Si/C powders using the arc melting method. The results show that the sample sintered at 80 s produced a near single-phase of Ti₃SiC₂ (99.2 wt.%) with a relative density of 88.9%. These results were confirmed by phase determination using XRD analysis and were supported with micrographs from FESEM/EDX analyses. The relative density and porosity of all samples were dependent on the formation of macropores in bulk samples and micropores in TiC_x grains. The proposed reaction mechanisms for the synthesis of Ti₃SiC₂ by arc melting is that Ti₃SiC₂ might be formed from TiC_x + Si, Ti₅Si₃C_x + C, and Ti₅Si₃C_x + TiC_x at early arcing time (≤ 10 s), while TiC_x + TiSi₂ take place at 15 s to 80 s. After 80 s, decomposition of Ti₃SiC₂ into TiC_x, TiSi₂ and C was observed.     

Ta4AlC3: Phase determination,polymorphism and deformation

Ta₄AlC₃, a new member of the M_n+1AX_n-phase family, has been synthesized and characterized (n = 1–3; M = early transition metal; A = A-group element; and X = C and/or N). Phase determination by Rietveld refinement of synchrotron X-ray diffraction data shows that Ta₄AlC₃ belongs to the P6₃/mmc space group with a and c lattice parameters of 3.10884  ± 0.00004 Å and 24.0776 ± 0.0004 Å, respectively. This is shown to be the α-polymorph of Ta₄AlC₃, with the same structure as Ti₄AlN₃. Lattice imaging by high-resolution transmission electron microscopy demonstrates the characteristic MAX-phase stacking of α-Ta₄AlC₃. Three modes of mechanical deformation of α-Ta₄AlC₃ are observed: lattice bending, kinking and delamination.     

One-dimensional antiferromagnetic behavior of a chiral molecular crystal, α′-(S,S-DMBEDT-TTF)2PF6

The synthesis, crystal and electronic structures, resistivity, magnetic susceptibility, and dielectric constant of the novel chiral crystal, α′-(S,S-DMBEDT-TTF)₂PF₆ [DMBEDT-TTF = dimethylbis(ethylenedithio)tetrathiafulvalene] are presented. The α′-type donor arrangement affords the one-dimensional antiferromagnetic behavior with J = ?40 K. The calculated band structure indicates the pseudo-one-dimensional interaction in the molecular side-by-side direction along the b-axis. The frequency-dependent dielectric constant suggests the charge disproportionation above 100 K. The non-centrosymmetric space group due to the composed chiral molecules affords the possibility of piezoelectricity.     

The effect of Zn on the microstructure and electrical properties of Mn1.17−xNi0.93Co0.9ZnxO4 (0 ≤ x ≤ 0.075) NTC thermistors

As-sintered Mn_1.17?xNi_0.93Co_0.9Zn_xO₄ (0 ≤ x ≤ 0.075) bodies consisted of two phases: a major Mn-rich phase with a cubic spinel structure and a minor NiO phase with a cubic structure. The Mn_1.17?xNi_0.93Co_0.9Zn_xO₄ ceramics were highly dense, ranging from 96 to 98% of the theoretical density and were microscopically homogeneous. The addition of Zn did not cause much change in the grain size and porosity. The obtained ρ₂₅, B_25/85 constant, and activation energy of the negative temperature coefficient (NTC) Mn_1.17?xNi_0.93Co_0.9Zn_xO₄ thermistors were in the range 1145–3696 Ω cm, 3218–3550 K, and 0.277–0.306 eV, respectively. This means that the electrical properties can be adjusted to desired values, depending on their Zn content. In particular, the resistivity and sensitivity were substantially enhanced with increasing Zn content.     

Doped and non-doped organic light-emitting diodes based on a yellow carbazole emitter into a blue-emitting matrix

A new carbazole derivative with a 3,3′-bicarbazyl core 6,6′-substituted by dicyanovinylene groups (6,6′-bis(1-(2,2′-dicyano)vinyl)-N,N′-dioctyl-3,3′-bicarbazyl; named (OcCz2CN)₂, was synthesized by carbonyl-methylene Knovenagel condensation, characterized and used as a component of multilayer organic light-emitting diodes (OLEDs). Due to its π-donor–acceptor type structure, (OcCz2CN)₂ was found to emit a yellow light at λ_max = 590 nm (with the CIE coordinates x = 0.51; y = 0.47) and was used either as a dopant or as an ultrathin layer in a blue-emitting matrix of 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi). DPVBi (OcCz2CN)₂-doped structure exhibited, at doping ratio of 1.4 weight %, a yellowish–green light with the CIE coordinates (x = 0.31; y = 0.51), an electroluminescence efficiency η_EL = 1.3 cd/A, an external quantum efficiency η_ext = 0.4 % and a luminance L = 127 cd/m² (at 10 mA/cm²) whereas for non-doped devices utilizing the carbazolic fluorophore as a thin neat layer, a warm white with CIE coordinates (x = 0.40; y = 0.43), η_EL = 2.0 cd/A, η_ext = 0.7%, L = 197 cd/m² (at 10 mA/cm²) and a color rendering index (CRI) of 74, were obtained. Electroluminescence performances of both the doped and non-doped devices were compared with those obtained with 5,6,11,12-tetraphenylnaphtacene (rubrene) taken as a reference of highly efficient yellow emitter.