Structural investigation of amorphous iron-nickel-boron alloys

Accurate X-ray diffraction investigation has been made of ten amorphous alloys having the compositions (Fe_0.6Ni_0.4)_100–x B _x with x=14 to 24 and (Fe_100–y Ni _y )₈₀B₂₀ with y=30 to 70 which were obtained by rapid quenching from the melt. Using the common Fourier analysis, the radial distribution function was calculated from which the distance and its number of the near neighbour atoms were derived. The present results indicate that the atomic distribution of metallic glasses with low boron content differs slightly from that observed previously for a number of metallic glasses of transition metalmetalloid type. The compositional effect, in particular the boron concentration effect, on the structure and characteristic structural features of amorphous Fe-Ni-B alloy glasses is discussed together with the mean atomic volume and the partial atomic volume of metalloid elements using the measured density data.     

Glass formation, optical properties and local atomic arrangement of chalcogenide systems GeTe-Cu and GeTe-In

Glass-forming regions of ternary Ge-Te-Cu and Ge-Te-In chalcogenide glasses are examined by differential scanning calorimeter and by X-ray diffraction. Glass transition and crystallization temperatures are about 120 °C To 260 °C, respectively higher than those of binary Ge-Te glass [T. Katsuyama and M. Matsumura, Infrared Optical Fibres (Adam Hilger, London, 1989) p. 212]. Only a small range of compositions after quenching the melting alloy is characterized by disordered state, but this range of composition is widened when using a vapor deposition technique. These compositions have two glass transition temperatures, showing the existence of phases in the sample. Both the Kissinger equation and modified Kissinger kinetic analysis were adopted to estimate activation energy and the reaction order of the process. Ge-Te-Cu and Ge-Te-In crystallized in two stages, nucleation and crystal growth. These two processes can be distinguished by exothermal crystallization patterns. An atomic radial distribution analysis has been made on bulk Ge₁Te₄In _x and Ge₁Te₄Cu _x with x = 0.1 by X-ray diffraction techniques. The radial distribution function (RDF) is discussed in terms of the structure factor F(s). Thin films of Ge-Te-Cu and Ge-Te-In are deposited on silicate glass and silicon wafer substrates by vacuum evaporation. The optical energy E _opt are determined from transmission and reflection data of a deposited films. The value of E _opt decreased by increasing metal additive such as Cu or In and discussed as a function of the conditions of their preparation such as substrate type.     

On the compositional dependence of the optical gap and structural properties of amorphous In x Se1−x thin films

The optical gap of the amorphous In _x Se_1–x thin film has been observed to decrease with increasing content of indium in the film (x). An attempt is made to interpret the compositional dependence of the optical gap in amorphous In _x Se_1–x thin film in an alloy-like approach. It has been found that introduction of higher concentrations of indium imparts greater stability to the structure of the indium selenium alloy. From the study of the radial distribution function (RDF) by X-rays it is observed that there is a correlation between the coordination number and the optical gap of indium selenide thin films.     

Lattice Effects in High-Temperature Superconducting Cuprates Revealed by Thin Film Single Crystals

In contrast to conventional superconductivity where phonons lead to the formation of Cooper pairs, in high-temperature superconductivity (HTSC), the role of electron–phonon coupling has long been neglected. The in-plane Cu–O bonds in HTSC cuprates show unconventional broadening at low temperature as carriers are doped. Here, we focus on the high-quality polarized X-ray absorption spectroscopy (XAS) data for a model HTSC system, (La,Sr)₂CuO₄ (LSCO). Thin film single crystal samples were prepared by state-of-the-art MBE, precisely controlling compositions. High-quality data was obtained by use of a segmented X-ray detector. The in-plane Cu–O radial distribution function (RDF) in LSCO (x=0.15) shows broadening as temperature is lowered, which shows a sharp drop at the critical temperature, which is followed by a gradual increase (disorder). Comparing the data with resistivity, we find a remarkable coincidence between the sharpening and the onset of superconductivity. Since the sharpening of RDF is interpreted as correlated motion of oxygen atoms (phase coherence due to superconductivity), the results demonstrate that the superconducting state directly relates to the unconventional oxygen displacements in a bond stretching mode. The results will be discussed in relation to local models of distortion of the different nature (metallic vs. insulating), that is, strongly influenced by strain.      

Structure changes on relaxation of differently cooled Pd0.835Si0.165 alloy glass

The radial distribution function (RDF) of X-ray diffraction was studied for liquid-quenched Pd_0.835Si_0.165 alloy glasses in relation to cooling conditions. The atomic distance (r ₁), total coordination number (n) and volume (V) are obtained by a first peak of RDF. The faster the cooling rate, the larger ther ₁,n andV become. Based on the relaxation theory, we show linear changes inr ₁,n andV with the sample thickness (D) which indicates the reciprocal cooling rate. log₁₀(r ₁ – 2.826) = –1.92 – 2.58D log₁₀ (12.83 –n) = 0.130 – 2.50D log₁₀(V – 7.95) = 0.011 – 2.80D The volume change is mainly dominated byn.     

A high-energy X-ray diffraction, P and B solid-state NMR study of the structure of aged sodium borophosphate glasses

The structure of aged melt-quenched sodium borophosphate glasses of composition (P₂O₅)₄₀(B₂O₃)_x(Na₂O)_60−x (with x in the range 10–40) has been studied by high-energy X-ray diffraction (HEXRD), ³¹P and ¹¹B magic angle spinning (MAS) NMR. Similar to the fresh samples, both POP and POB linkages are found to be present in these glasses. All three techniques show that the cross-linking between borate and phosphate units increases with boron oxide content. Distinctively upon aging, the glass is found to hydrolyze causing the network to degrade. At the same time, crystalline phases are now also observed. XRD and DTA show that the samples have a higher tendency towards crystallization with increasing boron oxide content upon exposed to moisture. ³¹P and ¹¹B MAS NMR results are in agreement with these findings. TGA data show that samples with higher boron oxide content take up more moisture upon aging, suggesting that crystallization may be associated with glass hydrolysis. HEXRD results also suggest that sodium ions are preferentially associated with borate units with increasing boron oxide content.     

Chemically prepared Fe-B ultrafine amorphous alloy particles: influence of the way of mixing reactants

Fe-B ultrafine amorphous alloy particles have been prepared by the addition of FeSO₄ solutions into KBH₄ solutions. The reaction was found to automatically maintain constant pH levels in a basic medium and produced Fe-B samples with higher boron content as compared to the reaction for the addition of KBH₄ solutions into FeSO₄ solutions. The latter reaction automatically maintained constant pH levels in an acidic medium. The mechanism of the overall reaction between FeSO₄ and KBH₄ in aqueous solution is composed of three simple independent reactions which are shown to be valid for both addition routes for the reaction. The concentration and addition rate of FeSO₄ solutions were also found to significantly influence the boron content and properties of the produced Fe-B samples. This revised version was published online in November 2006 with corrections to the Cover Date.     

X-ray studies on microstructural characterization of tantalum substituted tungsten mixed molybdenum diselenide; W0·65Mo35−x Ta x Se2 (0≤x≤0·35)

The wide angle X-ray diffraction on W_0·65Mo_5−x Ta _x Se₂ (0≤x≤0·35) compounds have been used for calculation of the crystallite size by method of variance and Fourier technique and for microstructural parameters purposes. The crystallite size showed the decreasing trend with increasing composition up tox=0·15 and after that it increased sharply. On the contrary, mean fractional change in interlayer spacing, fractions of the planes affected by defects, dislocation density, and root mean square strain showed the opposite trend. The crystallite size anisotropy and stacking fault probability showed 1:1 correspondence in their variation with composition. The radial distribution analysis have also been employed to find out the information about the inter atomic distances, coupling constants and mean square displacements for different pairs of atoms. These results have been interpreted in terms of difference in packing of layers in these compounds.     

Mechanical alloying of Fe-B alloys

Mechanical alloying (MA) of Fe-B alloy systems using a conventional ball mill has been performed. The structure change of Fe_100?x B _x for the composition range 10≤x≤90 has been investigated using X-ray diffractometry, thermal analysis, transmission electron microscopy, scanning electron microscopy and Mössbauer spectroscopy. According to the X-ray diffraction analysis, the sequences of transformation have been classified into three groups,x≤20, 25≤x≤35 andx≥50 for Fe_100?x B _x . The amorphous phase whose composition is nearlyx=30, first appeared for the whole composition range. This amorphous phase changed into a tetragonal Fe₂B-like compound on further milling for 1000 h. On further milling of thex= 50 sample, the Fe₂B compound phase disappeared and orthorhombic FeB compound appeared.     

Refractive index and density of alkali lime borogermanosilicate glasses

Refractive index and density data of glasses having molar compositions 15% A ₂O-10% CaO-45% SiO₂-(30–x%) GeO₂-x% B₂O₃ with A=Na or K are reported. From these data the molar refraction and the contribution of oxygen to the molar refraction are calculated. The co-ordination of germanium and boron in these glasses is discussed. At x=0, GeO₆ octahedra are observed which are gradually transformed into GeO₄ tetra-hedra as the GeO₂ is replaced by B₂O₃. In B₂O₃-rich glasses no GeO₆ octahedra are present and the structure of the B₂O₃-rich glasses is found to be the same as that of comparable alkali borosilicate glasses.     

On the corrosion characteristics of some commercial magnetic metallic glasses in NaCl solution

The corrosion characteristics of six commercial magnetic metallic glasses, namely Fe₇₈B₁₃Si₉ (Metglas 2605-S-2), Fe₆₇Co₁₈B₁₄Si (Metglas 2605 Co), Fe₄₀Ni₄₀B₂₀ (Vitrovac 0040), Fe₃₉Ni₃₉Mo₂(SiB)₂₀ (Vitrovac 4040), Fe₄₀Ni₃₈Mo₄B₁₈ (Metglas 2826 MB) and Fe₄₀Ni₄₀P₁₄B₆ (Metglas 2826) in which iron and boron are common base elements have been studied by immersion tests and potentiostatic techniques in various concentrations of NaCl solutions at room temperature. In exposure for up to six days, weight loss observations indicated that the corrosion rates in 3.5% NaCl were in the following increasing order: 2826 < 4040 < 0040 < 2826 MB < 2605 Co < 2605-S-2. During exposure for up to four hours under open-circuit conditions, 2826 alloy showed the noblest behaviour while 2605-S-2 was the least noble. All the alloys, except 2826, showed rapid dissolution without any passivation during anodic polarization. Phosphorus addition to Fe-Ni-B glass enhanced the active dissolution and resulted in the formation of a black prepassive film in the active region (0.2V) which becomes protective in the passive region (0.3 to 1.25V). The values ofI _crit. andI _pass. (the critical and passive current densities) decreased with a decrease of concentration from 3.5 to 0.01% NaCl, while in 0.001% NaClI _pass. slightly increased and the passivation potential range decreased. The corrosion resistance of Fe-B metallic glasses increased with metal addition in the order Co < Mo < Ni and with metalloid addition in the order Si < P.     

Development of in-house fast X-ray diffraction apparatus and its application to the supercooled liquid Pd40Ni10Cu30P20 alloy

A fast X-ray diffraction apparatus has been developed for obtainingthe local structures of bulk metallic glasses at the supercooled liquid state by applying the Debye–Scherrer camera geometry in combination with a curved position sensitive proportional counter. This arrangement makes it possible to eliminate the time loss due to angular motion of a counter and to do a very short time X-ray measurement when using the conventional in-house X-ray source. The usefulness of this new apparatus was confirmed by obtaining the radial distribution functions of silicon powder and SiO₂ glass sample within one hundred seconds. Then, the short-range ordering structure of the supercooled liquid Pd₄₀Ni₁₀Cu₃₀P₂₀ alloy was observed as a function of time at 583 K.     

Influence of modifier oxides on some physical properties of antimony borate glass system doped with V2O5

Three series of glasses, of the composition 20 MO (M = Ca, Pb, Zn)–40 Sb₂O₃–(40 − x) B₂O₃:xV₂O₅, with six values of x ranging from 0 to 1 mol% were prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy, EDS and differential scanning calorimetric techniques. The comparison of DSC data among the three series has indicated high glass forming ability for ZnO mixed glasses. Dielectric properties over a range of frequency and temperature, optical absorption, ESR spectra at room temperature and IR spectra have been investigated. The variations observed in all these properties due to different modifiers as a function of the concentration of V₂O₅ have been analyzed in the light of different oxidation states and environment of vanadyl ions in these glasses. The analysis of these results indicated that the ZnO mixed glasses are more stable against devetrification and possess high insulating strength when compared with PbO and CaO mixed glasses.     

Atomic arrangement in the glassy semiconductor Ge30As20Se50

Two tridimensional models of Ge₃₀As₂₀Se₅₀ amorphous alloy have been built by theoretical simulation of the experimental Radial Distribution Function (RDF) calculated from the X-ray diffraction data of a powder sample of the studied alloy. The models are discussed from topological and geometric point of view and an analysis of the main structural parameters is carried out in order to proposed a real average structure of the material. Both models fit the experimental RDF and abide by the geometrical conditions. But a model formed by clusters of tetrahedra with some overlapping linked to each other by As and Se chains has been considered more probable from topological considerations. This model has a better agreement with the shortrange order supposed from the RDF preliminary analysis, glass transition temperature and electronic structure.     

Neutron diffraction study on the medium and short-range order of ternary chalcogenide glasses

Glasses from Ge_xAs_40–xS₆₀, Ge_xAs_40–xSe₆₀, Ge_xSb_40–xS₆₀ and Ge_xSb_40–xSe₆₀ families have been investigated by neutron diffraction. The well expressed first sharp diffraction peak of the neutron spectra at Q = 10–14 nm^–1 has been explained by a pseudo-binary model of the structure of studied chalcogenide glasses. The amplitude of this interference maximum increases with Ge-content in all investigated samples. Experimental radial distribution functions show that the basic structural units, GeS(Se)₄ tetrahedra and As(Sb)S₃ or As(Sb)Se₃ pyramids persist in glassy state for the whole range of studied compositions. Crystal-like model distribution functions have been used to describe the short-range order observed. A shortening of heteropolar bonds in S-containing glasses as well as an increase of heteropolar bonds length in Se-containing glasses has been found.     

Development of in-house fast X-ray diffraction apparatus and its application to the supercooled liquid Pd40Ni10Cu30P20 alloy

A fast X-ray diffraction apparatus has been developed for obtaining the local structures of bulk metallic glasses at the supercooled liquid state by applying the Debye–Scherrer camera geometry in combination with a curved position sensitive proportional counter. This arrangement makes it possible to eliminate the time loss due to angular motion of a counter and to do a very short time X-ray measurement when using the conventional in-house X-ray source. The usefulness of this new apparatus was confirmed by obtaining the radial distribution functions of silicon powder and SiO₂ glass sample within one hundred seconds. Then, the short-range ordering structure of the supercooled liquid Pd₄₀Ni₁₀Cu₃₀P₂₀ alloy was observed as a function of time at 583 K.     

Buckling Patterns of Graphene–Boron Nitride Alloy on Ru(0001)

Buckling nanopatterns of monoatomic layer 2D materials on metal substrates attract significant attention due to their rich interface morphology affecting electronic applications. An experimental–theoretical study of a 2D boron–nitrogen–carbon (B _{x /2}N _{x /2}C_1−x ) alloy on a Ru(0001) surface is conducted and a profound relation between the composition x and the degree of buckling is discovered. Experimentally, real carbon–boron–nitrogen alloys on the Ru(0001) surface are demonstrated and various morphologies of pure and mixed compounds are shown. Density functional theory calculations are further carried out using the supercells of graphene, hexagonal boron nitride (h‐BN), and random BNC on Ru(0001), as well as Monte Carlo simulations for elucidating the kinetics of their growth. The results show that unlike pure compounds (h‐BN or C), the carbon–boron–nitrogen mix on Ru(0001) mostly exists in an uncorrugated form, thus greatly improving the interface contact. The likely cause of the diminished corrugation is a softening of bond angular interactions in the alloy relative to the pure phases.     

Local ordering structure of meta-kaolinite and meta-dickite by the X-ray radial distribution function analysis

X-ray diffraction measurements on the structure of meta-kaolinite and meta-dickite have been carried out to obtain the radial distribution function (RDF). The distances and corresponding coordination numbers for Si-O and Al-O pairs were estimated by applying the pair function method. The SiO₄ tetrahedron remains unchanged in the dehydrated samples presently investigated, and the oxygen coordination number around aluminium was also found to be four. This implies the overall preference of AlO₄ tetrahedron at the expense of the parent AlO₂ (OH)₄ octahedron.     

Quantitative X-ray fluorescence analysis of As-Se glasses and films

The concentrations of arsenic and selenium in As_{100 − x} Se _x glassy alloys and related films have been determined by the X-ray fluorescence spectroscopy using the external standard technique. It is demonstrated that the proposed approach allows the compositions of As_{100 − x} Se _x glasses and films to be quantitatively determined with an accuracy of Δx = ±0.02.