Substitution Of Antimony Research Articles

Substitution of Antimony by Tin and Tellurium in n-Type Skutterudites CoSb2.8Sn x Te0.2−x

We have studied the substitution of antimony by tin and tellurium in n-type skutterudites CoSb2.8SnxTe0.2� x. The samples were made by ball milling ingots and hot pressing the ball-milled nanopowder. Rather than filling the cage of the structure, we aimed to use disorder in pnictogen rings by elemental substitution of Sb by Sn and Te. In skutterudite CoSb3, the dominant heatcarrying phonons are associated with the vibrational modes of the Sb-rings; disorder in the rings can be an effective way to suppress the thermal transport. By suitably tuning the contents of Sn and Te in the skutterudites, we have suppressed the thermal conductivity and achieved a power factor of � 42 l Wc m � 1 K � 2 at 530C. A peak thermoelectric figure of merit (ZT) reaches � 1.1 at 530C for CoSb2.8Sn0.005Te0.195. This ZT value is comparable with that of some of the single-filled skutterudites.

Polymorphism and properties of Bi2WO6 doped with pentavalent antimony

Antimony-containing solid solutions isostructural with bismuth tungstate, Bi2WO6, have been prepared in air as polycrystalline samples by solid-state reactions and as single crystals by unseeded flux growth. The antimony in the solid solutions is in a pentavalent state and substitutes for tungsten in the structure of Bi2WO6. The Bi2W1−xSbxO6−y solid solutions have been shown to exist in the composition range 0⩽x⩽0.05. We have examined the effect of Sb5+ doping on the polymorphism and properties of Bi2WO6. In contrast to undoped Bi2WO6, antimony-substituted bismuth tungstate does not completely transform into its high-temperature, monoclinic phase at 960°C and remains two-phase up to temperatures approaching its melting point. Antimony substitution for tungsten has a weak effect on the temperatures of the ferroelectric phase transitions. Heterovalent substitution of Sb5+ for W6+ is accompanied by the formation of extra oxygen vacancies and an increase in the electrical conductivity of the solid solutions by one to two orders of magnitude relative to undoped Bi2WO6.

Vibrational Studies of Zinc Antimony Borophosphate Glasses Doped Rare Earth

Zinc antimony borophosphate glasses has been determined for [10P2O5 –40B2O3 –xSb2O3 –(50–x)ZnO] and composition of [10P2O5 – 40B2O3 –40Sb2O3 –10ZnO] has been doped with 1 mol% of rare earth (Eu, Nd, Sm, Er). The functions of compositional changes on their structural features were examined using X–Ray Diffraction (XRD) to detect the amorphousity phase present. While Fourier Transform Infrared (IR) Spectroscopy were used to identify the presences of vibrational modes and band assignments of phosphate, borate, antimony, zinc and Rare earth ion in the system. XRD results expose that crystalline phase changes with different amount of zinc and antimony substitution. Hydroxyl group absorption also vary due to this composition changes and clearly shown in IR spectroscopy in the ranges 1400–4000 cm–1. Result of IR spectroscopy indicated that bands around 1440 cm–1 and 760 cm–1 was ascribed to the vas(B–O–B) and vs(P–O–P) vibration respectively. The changes of this vibration indicated that P–O–B linkage was formed near 660 cm–1. The modification of zinc antimony borophosphate glasses with rare earth was studied and showed present of rare earth ion in the glass system does not change the structural features.

Superconducting Properties of Ag and Sb Substitution on Low-Density YBa2Cu3O δ Superconductor

The effects of silver (Ag) and antimony (Sb) substitution on low-density YBa2Cu3O δ (YBCO) superconductor were investigated. Two series of sample with a nominal composition of YBa2−x Ag x Cu3O δ and YBa2−x Sb x Cu3O δ where x=0.05, 0.10, 0.15, 0.20, 0.30, 0.40 and 0.50 were synthesized and characterized. All Ag-doped samples showed metallic behavior at the normal state and T C onset was found at 90 K. T C zero decreased as the Ag concentration increased. Optimum Ag concentration was achieved at x=0.20 where T C zero has the highest value of 87 K and J C at 70 K is 16.50 A/cm2. For Sb-doped case with x≤0.30, the samples showed metallic behavior above T C onset while semiconducting behavior was shown for x≥0.40. The optimum Sb concentration was achieved at x=0.15 where T C zero is 85 K and J C value measured at 70 K is 2.75 A/cm2. T C onset and T C zero were found to decrease toward higher Sb concentration. The crystallographic structure transformed to tetragonal in Sb-doped samples of x≥0.30 while other samples remain orthorhombic.

MICROSTRUCTURAL DEPENDENCE OF MAGNETIC PROPERTIES OF Sb5+ SUBSTITUTED LITHIUM FERRITES

This paper reports the influence of antimony substitution on the magnetic properties of Lithium ferrite sintered at 1200°C. The samples with compositional formula [ Li 0.5+x Sb x Fe 2.5-2x] O 4 (where x = 0.0, 0.1, 0.3, 0.6, 0.8 and 1.0) were prepared by standard ceramic route method. The Curie temperature (Tc) was found to be highest at 720°C for x = 0 compound and decreased with increasing x (i.e., Sb 5+ substitution). Saturation magnetization, coericivity, remanent magnetization were studied as a function of Sb content and grain size. The results of initial permeability showed anomalous variations as x varied from 0.0 to 1.0. The maximum initial permeability was observed for x = 0.3 compound. The morphological studies were performed by SEM and the mean diameter of the grain size of the samples was determined and showed correlation with magnetic properties.

The effect of antimony doping on the transport and magnetic properties of Ce(O/F)FeAs

Oxypnictides of types CeOFeAs1 − xSbx, CeO0.9F0.1FeAs1 − xSbx and CeO0.8F0.2FeAs1 − xSbx have been synthesized in order to understand the effective change in electron doping by the twin effectsof F − incorporation and the variation in Fe–As bonding by substitution of a larger ion (Sb) at the Assite. All the compounds crystallize in a tetragonal ZrCuSiAs-type structure (space group:P4/nmm). Both the latticeparameters (a and c) increase with the increase in antimony substitution due to the larger ionic size of antimony.CeOFeAs1 − xSbx (x = 0.1, 0.2and 0.3) compounds were found to be semimetallic, like the parent CeOFeAs. Substitution of Sb inCeOFeAs1 − xSbx resultsin a shift of the temperature of the resistance anomaly corresponding to the structural phase transition.CeO0.9F0.1FeAs1 − xSbx (‘x’ = 0, 0.05, 0.1 and 0.15) was superconducting with a maximum transmission temperature (Tc) of 43.17 K for‘x’ = 0.1, which is higher thanthe antimony-free CeO0.9F0.1FeAs (Tc = 38 K). Further increasein antimony (x > 0.15) results in the suppression of superconductivity. Similarly, Sb doping in optimally electron dopedCeO0.8F0.2FeAs superconductor leads to the lowering of the superconducting transition temperature (‘x’ = 0.1) and further increase in antimony substitution (‘x’ > 0.1) leads to a loss ofsuperconductivity. CeO0.8F0.2FeAs0.9Sb0.1 shows a very high value of the upper critical fieldHc2(0) (137 T) as comparedto Sb-free CeO0.8F0.2FeAs. In this paper, we discuss the first example among electron-doped oxypnictide superconductors wherethe Tc increases as a result of a decrease in chemical pressure (an increase in lattice parameters).

Variable temperature performance of intermetallic lithium-ion battery anode materials

Although a variety of cathode and electrolyte materials have been studied and commercialized over the past two decades, nearly all commercial cells have used a graphitic carbon anode. Several reasons exist for this choice—including cost, low insertion voltage, and ease of use in the cell manufacturing process. However as uses for lithium-ion batteries expand, alternative anodes that may offer better energy and power capability are being explored. For transportation-oriented purposes, anodes based on simple lithiated Zintl compounds, e.g. Li 17Sn 4, or intermetallic insertion anodes offer significant advantages in capacity (volumetric and gravimetric) and stability in the cell environment that make them attractive candidates for future cell chemistries. Within this context, little however is known about how these alternative anode materials perform as a function of temperature, which is important for applications where operation at temperatures as low as −30 °C can be expected. In this study we evaluated a series of intermetallic insertion anodes that operate by a simple metal displacement mechanism. We have found that for Cu 6Sn 5, Ag/Cu 6Sn 5, and Cu 2Sb, the drop-off in performance with temperature is in line with that observed for a commercial graphite-based anode and indicates that additional variables such as cation diffusion through the electrode passivation film or the electrochemical double layer may be playing an important role that is independent of the underlying anode material. We additionally characterized the NiAs-type mineral Sorosite (CuSn 0.9Sb 0.1), as various literature reports had indicated that substitution of antimony for tin eliminated the need for interstitial copper, however powder X-ray diffraction studies of samples made by annealing or high energy ball milling indicated mixed phase samples.

EFFECT OF ANTIMONY SUBSTITUTION FOR NIOBIUM ON THE CRYSTAL STRUCTURE, PIEZOELECTRIC AND DIELECTRIC PROPERTIES OF (K0.5Na0.5)NbO3 CERAMICS

The effect of antimony ( Sb ) substitution for niobium ( Nb ) on potassium sodium niobate (KNN) ceramic was investigated with respect to the densification behaviour at different sintering temperatures, microstructure and electrical properties. A small amount of Sb 5+ was added while simultaneously lowering the amount of Nb 5+ and in this study of the ( K 0.5 Na 0.5)( Nb 1-x Sb x) O 3 system, x content was varied from 0 to 14 mol%. Our results show that Sb 5+ slightly increased the optimum sintering temperature for KNN but above 8 mol%, its resistivity and piezoelectric properties decreased. As the amount of Sb 5+ substituted is increased, the structure of the ceramic transformed from orthorhombic to pseudo-cubic which led to slight shrinkage in the unit cell volume. Microstructural examination revealed that above 10 mol%, a second phase ( K 2 NaSb 3 O 9) was formed which segregated mainly to the grain boundary while the quantitative EDX analysis showed that there was A-site vacancy due to loss of the alkali elements. The two phase transitions points, Curie temperature (T C ) and the tetragonal to orthorhombic (T T-O ) shifted to lower temperature with increasing Sb 5+ content and above 10 mol%, the T T-O shifted to below room temperature. The dielectric loss slightly increases with increasing Sb 5+ content up to 200°C. There was an improvement in the piezoelectric properties with ≤ 6 mol% Sb content while optimum properties were obtained with 4 mol% (K P = 0.46, Q m = 6.2, N P = 2296).

Investigation of the Thermoelectric Properties of the Series TiCo1–xNixSnxSb1–x

AbstractThe effect of the simultaneous substitution of cobalt by nickel and antimony by tin in the solid solution TiCo1–xNixSnxSb1–x was systematically investigated. The number of valence electrons does not change by this substitution and therefore the resistivity stays semimetallic or semiconducting. The series were synthesized by arcmelting and the thermoelectric properties were determined. It was found out that the substitution of cobalt and antimony by nickel and tin reduces the thermal conductivity to 2 W·m–1·K–1 at 400 K. The reduction is caused by titanium rich prolate micro structures that were found by energy dispersive X‐ray spectroscopy investigations. The Seebeck coefficient and the resistivity increase with increasing amounts of cobalt and antimony. The highest Power factor was found for the composition TiCo0.8Ni0.2Sn0.8Sb0.2 at 900 K with the value of 9.2 μW·cm–1·K–1.

Electrochemical hydrogenation and corrosion behaviour of LaCo4.8M0.2 alloys

AbstractHydrogen absorption properties and the corrosion characteristics of three LaCo4.8M0.2 alloys (where M ≡ antimony, magnesium or bismuth) have been investigated using electrochemical techniques. Absorption of hydrogen and corrosion behaviour of LaCo4.8M0.2 alloys have been compared with LaCo5 intermetallic compound. Typical potentiokinetic polarisation curves in 6 M potassium hydroxide solution showed that modification of LaCo5 by partial substitution of antimony, magnesium or bismuth for cobalt resulted in lower anodic currents in the passive range. The substitution does not significantly affect the shape of potentiokinetic polarisation curves in 0.5 M sulphate solutions for pH 2 and 7. Partial substitution of cobalt with bismuth in LaCo5 alloy increases the effectiveness of absorption of cathodically evolved hydrogen in strong alkaline solutions.

Effect of antimony substitution on structural and electrical properties of LaFeO 3

Fine crystalline LaFeO 3 and antimony-substituted compounds have been prepared by co-precipitation method. The as synthesized materials have been sintered at 1000 °C for single-phase compound formation and evaluated for their electrical and structural properties. TG/DTA studies ascribed that the precursor powders have undergone rapid changes during the transformation of LaFeO 3 and substituted compounds. XRD data reveal the presence of well-defined sharp peaks, indicating the single-phase perovskite structure of LaFeO 3 and polycrystalline structure of LaFeO 3 and Sb 2O 3 compounds. The FT–IR spectra exhibit an absorption band corresponding to Fe–O stretching vibration, which is shifted on the substitution of Sb 3+ ions. The temperature dependent d.c. conductivity shows the semiconducting behavior of the synthesized materials. The band gap values are found to increase upto x = 0.4 and decrease on further increase in concentrations of the Sb 3+ ions. The decrease in dielectric constant with increasing frequency explained the Maxwell–Wagner Interfacial polarization model.

WITHDRAWN: Effect of antimony substitution on structural and electrical properties of LaFeO3

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Erbium-rich region of the ternary Er–Ni–Sb system: Solid state phase equilibria at 1073 K and crystal structures of the new ternary compound Er 5Sb 3− xNi x ( x = 0.48) and both modifications of Er 5Sb 3

The solid state phase equilibria in the Er-rich region of the ternary Er–Ni–Sb system were determined at 1073 K using experimental techniques such as X-ray diffraction, scanning electron microscopy and electron probe microanalysis. In addition to the ternary phase Er 5Ni 2 Sb previously reported, a new phase Er 5Sb 3− x Ni x ( x = 0.48) was obtained, the structure of which was solved from X-ray single crystal data: space group Pnma, a = 1.17522(3) nm, b = 0.90437(3) nm, c = 0.79144(5) nm, R 1 = 0.067, w R 2 = 0.070 . Moreover, for the first time, both modifications of the binary antimonide Er 5Sb 3 were obtained and their structures were studied from X-ray powder diffraction data. The low-temperature form belongs to the Mn 5Si 3 type: space group P6 3/ mcm, a = 0.88062(4) nm, c = 0.62139(9) nm, R I = 0.074, R p = 0.150, while the high-temperature form exhibits the β-Yb 5Sb 3 type: space group Pnma, a = 1.16897(3) nm, b = 0.91425(3) nm, c = 0.80217(2) nm, R I = 0.077, R p = 0.125. According to these results, one can conclude that the substitution of antimony by nickel at 1073 K in the ternary phase Er 5Sb 3− x Ni x tends to stabilize the β-Yb 5Sb 3 type.

Systematic Variation in Galena Solid-Solution Compositions atSanta Eulalia, Chihuahua, Mexico

Argentiferous galena is the main silver-bearing phase at both the East and West camps of the Santa Eulalia district, Chihuahua, Mexico. The silver occurs as a coupled substitution of Ag and Sb for Pb in PbS with compositions ranging from 0.04 to 5.9 atomic percent (at. %) Ag and 0.10 to 7.2 at. percent Sb. Correlation analysis between Ag and Sb resulted in r values of 0.97 and 0.99 (significant at the 98% confidence level) for direct-current plasma-atomic emission spectroscopy (DCP-AES) and microprobe analysis of galena, respectively. Discrete and crystallographically oriented inclusions of diaphorite (usually 1 μ m or smaller) were common in high silver-antimony galenas and rare in low silver types (when present, tend to be larger). These inclusions were most abundant in the core zones of the crystals and rare on the edges. Spatial and temporal variations in Ag-Sb concentrations and ratios in galena were found mainly in the West camp of the district. High silver galenas (maximum 5.9 at. %) are confined to skarn zones or deep manto and chimney areas. The Ag/Sb ratio increases in galena from depth (0.88) to the surface (1.04) and from south (0.76) to north (0.94), following zonation and flow patterns established in previous investigations. Differences in Ag-Sb substitution in galena are also seen in different mineralization types: breccia zones, deep mantos, and chimneys contain more Ag-Sb (3.5 at. % avg) and have lower Ag/Sb ratios (avg ratio = 0.88) than the upper mantos, silicate and calc-silicate orebodies, which have lower Ag-Sb concentrations (2.2 avg at. %) but higher ratios (avg ratio = 1.00). Silver and antimony substitution also correlates with sulfur isotope variation in the district. Within individual orebodies, the δ 34S value increases with decreasing silver and antimony concentrations in galena. The solid-solution compositional variations in galena coupled with sulfur isotope values are a useful tool for inferring fluid paths and appear to reflect fluid evolution. At Santa Eulalia, silver is disseminated to various degrees throughout the orebodies and galena solid-solution concentrations appear to be controlled by subtle physical and/or chemical gradients. This contrasts with volcanic-epithermal systems in which significant physiochemical perturbations (large thermal and pressure gradients, boiling, etc.) lead to dumping of precious metals and semimetals as sulfosalts in bonanza zones. Relatively low concentrations of other potential ore-forming elements, namely copper and bismuth, also precluded the formation of a complex suite of silver sulfosalts and antimonian-argentiferous galena precipitated instead. Sulfosalts at Santa Eulalia are localized to upper mineralized zones as breccia void fillings, indicative of limited zones of boiling.

Crystal structure and dielectric relaxation studies of the [N(CH3)3H]3Sb2(1−x)Bi2xCl9 mixed crystals

The influence on ferroelectric properties of a partial substitution of antimony by bismuth in the [N(CH3)3H]3Sb2Cl9 (TMACA) crystals are investigated by dielectric and x-ray diffraction methods. The dielectric relaxation in the [N(CH3)3H]3Sb2(1−x)Bi2xCl9 (TMACAB) mixed crystals (x=0, 0.07, 0.33, 0.38, and 1) is studied in the frequency range between 20 Hz and 1 GHz and temperature range between 170 and 375 K. The ferroelectric properties of mixed crystals are preserved for the Bi concentration less than 0.33. The increase of the Bi concentration distinctly influences the phase transition temperature but only weakly the dynamical properties of those crystals. The dielectric response of the ferroelectric TMACAB crystals is characterized by a presence of two relaxation modes. One of them behaves critically and the other one is only thermally activated. The disappearance of ferroelectric properties is connected with the essential change of crystal structure of mixed compounds. The anionic sublattice of nonferroelectric TMACAB (x>0.33) (R3̄c space group) instead of two-dimensional layers is composed of the isolated Sb2(1−x)Bi2xCl9 bioctahedral units.

Electrical properties of BaSnO3 in substitution of antimony for tin and lanthanum for barium

Polycrystalline materials of BaSn1−xSbxO3−δ and Ba1−yLaySnO3−δ were prepared. Substitutional solubilities of antimony for tin and lanthanum for barium, respectively, in BaSnO3 were obtained to be x=0.18 for BaSn1−xSbxO3−δ and y<0.052 for Ba1-yLaySnO3−δ. The X-ray photoemission spectroscopy measurements showed the valence of antimony and tin is mixed in our samples of BaSn1−xSbxO3−δ. At lower temperature, magnetic susceptibilities of BaSn1−xSbxO3−δ and Ba1−yLaySnO3−δ satisfy the Curie law, indicating the existence of non-interacting localized electrons at the Sn4+ site, and forming a Sn4++e− state in these systems. By substitution of antimony and lanthanum in BaSnO3, the conductive properties are semiconductor-like. To explain this conductive behaviour, three types of mechanism were taken into consideration.

Magnetostrictive behaviour observed in MnAs/sub 0.92/Sb/sub 0.08/ over the field range 0 to 850 kA/m

Strain measurements were conducted on polymer bonded samples of MnAs and MnAs/sub 0.92/Sb/sub 0.08/. A substantial increase in the strain measured at 850 kA/m was exhibited upon substitution of antimony for arsenic. Anisotropy within the polymer bonded compact was induced using an aligning field of 800 kA/m. Values of 230 ppm and 110 ppm were obtained for the two perpendicular orientations at 850 kA/m.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

19F and 31P magic-angle spinning nuclear magnetic resonance of antimony(III)-doped fluorapatite phosphors: Dopant sites and spin diffusion.

Phosphors based on calcium fluorapatite [${\mathrm{Ca}}_{5}$F(${\mathrm{PO}}_{4}$${)}_{3}$] doped with small amounts of ${\mathrm{Sb}}^{3+}$ as an activator are used in most fluorescent lamps. We have used quantitative $^{19}\mathrm{F}$ and $^{31}\mathrm{P}$ magic-angle spinning nuclear magnetic resonance (MAS-NMR) to study seven samples of calcium fluorapatite containing 0.0--3.0 wt % ${\mathrm{Sb}}^{3+}$ in order to determine the site of antimony substitution. The $^{31}\mathrm{P}$ MAS-NMR spectra of fluorapatite containing 3.0, 2.1, and 1.3 wt % antimony contain a single sharp peak at 2.8 ppm indistinguishable from undoped fluorapatite, and show no additional peaks attributable to the influence of antimony. The $^{31}\mathrm{P}$ MAS-NMR spectra of the model compounds ${\mathrm{SbPO}}_{4}$, ${\mathrm{Sr}}_{1.03}$${\mathrm{Ca}}_{8.97}$${\mathrm{F}}_{2}$(${\mathrm{PO}}_{4}$${)}_{6}$, ${\mathrm{Sr}}_{5}$F(${\mathrm{PO}}_{4}$${)}_{3}$, and ${\mathrm{Ba}}_{5}$F(${\mathrm{PO}}_{4}$${)}_{3}$ were also obtained. The $^{19}\mathrm{F}$ MAS-NMR spectra of the antimony-doped samples exhibit, in addition to the main peak at 64.0 ppm (downfield from ${\mathrm{C}}_{6}$${\mathrm{F}}_{6}$) arising from unperturbed fluorapatite, a shoulder at 65.6 ppm, and a sharp peak at 68.6 ppm. The measured spin-lattice relaxation times ${\mathit{T}}_{1}$ of these antimony-related peaks are equal in all cases to that of the main peak in a given sample, and vary from 129 to 378 sec, indicating that these peaks arise from apatitic fluoride ions perturbed by antimony.Quantitative studies reveal that the 68.6-ppm peak arises from two fluoride ions and the 65.6-ppm shoulder from one fluoride ion per ${\mathrm{Sb}}^{3+}$ ion incorporated into the lattice. The selective population anti-z and rate of transfer to adjacent nuclei (SPARTAN) pulse sequence used to measure spin diffusion by selectively inverting the 68.6-ppm peak reveals the presence of cross-relaxation to the main peak at 64.0 ppm, but not to the shoulder at 65.6 ppm. Each ${\mathrm{Sb}}^{3+}$ ion thus appears to be perturbing fluoride ions in at least two different chains. An additional peak at 73.1 ppm observed in some samples is assigned to a second type of antimony(III) substitution, with a single fluoride ion perturbed by each antimony ion. The results in total provide detailed support for a substitution model in which antimony(III) occupies a phosphate site in the apatite lattice, with a ${\mathrm{SbO}}_{3}^{3\mathrm{\ensuremath{-}}}$ group replacing a ${\mathrm{PO}}_{4}^{3\mathrm{\ensuremath{-}}}$ group. Two types of substitution at this site appear to occur, depending upon which oxygen atom is replaced by the antimony lone electron pair.

Determination of the antimony substitution site in calcium fluorapatite from powder X-ray diffraction data

Comparison of powder X-ray diffraction data from a 2-2 wt% antimony-substituted calcium fluorapatite [0.185 Sb atoms per unit cell containing CaloF2(PO4)6] with data from an undoped sample shows electron density changes corresponding to antimony substitution at the Ca(2) (mirror) site. Many properties of this 2.2 wt% Sb sample indicate that it corresponds to commercial halophosphate phosphors of lower Sb concentration. Differing properties are shown by a 3.1 wt% Sb sample for which no diffraction evidence is found for substitution at the Ca(2) site, but for which electron density difference maps do suggest substitution at the Wyckoff 2(c) and 2(d) sites of P63/m, between Ca(l) (threefold) positions. Both Rietveld refinements and Fourier inversion of the differences between observed intensities were used to reach these conclusions.

The influence of the substitution of metallic elements on the thermal stability and magnetic properties of amorphous FeBSi alloys

We have studied the effect of the substitution of metallic elements on the Curie temperature T c induction, shape of the differential thermal analysis curve and crystallization temperature T x, of glassy Fe 79B 16Si 5 alloys prepared by planar-flow casting. Substitutions have been made for all three (iron, boron and silicon) components of the glass. Increasing concentration of the substituting elements leads to embrittlement, notably with niobium or tantalum. For the substitution of vanadium, chromium, niobium, manganese, molybdenum and tantalum for iron, we have obtained a linear decrease of T c, independent of the substituted species. However, T c increases with either nickel, tin or antimony substitution. We have found that the substitutions produce stronger effects when made for either boron or silicon. Substitutions for iron decrease the induction at 10 Oe, except for nickel, where this remains unchanged. For the crystallization temperature T x, we have observed that all the elements lead to an increase, except for nickel, when substituted for iron. The changes in T x are essentially related to the size effect.