Structure and stability of rapidly quenched Al86Cr14−x Fe x alloys

The structural and thermal properties of melt spun Al₈₆Cr_14–x Fe _x , alloys have been investigated using X-ray diffraction, transmission electron microscopy, electron diffraction and differential thermal analysis. Electron diffraction patterns indicate that all alloys contain quasicrystalline nodules with icosahedral symmetry in a matrix of f cc aluminium. Microscopically the alloys fall into two categories; those with x 6 and those withx > 6. The first class alloys shows large (>1m) icosahedral crystallites with well defined dendritic crystallite growth and sharp quasicrystalline X-ray diffraction peaks. The latter alloys show quasicrystalline crystallites which are predominantly much smaller as well as considerably broadened X-ray diffraction peaks. Thermal analysis measurements indicate that the activation energy for crystallization in these alloys is about 1.5 eV.     

Formation and properties of amorphous (Fe1−x Nb x ) l B100−l

Amorphous (Fe_1–x Nb _{x l} B_100–l alloys with 0 x 0.15 and 74 T _g, crystallization temperatureT _x, and microhardnessH _v, but to decrease the magnetization and Curie temperatureT _c. The effects of niobium onT _x,H _v, andT _c in iron-based amorphous alloys are similar to those of chromium, manganese, molybdenum, tungsten and vanadium.     

Thermodynamic study of the magnetic ordering of Fe3−x Mn x Si alloys

The compounds Fe_3–x Mn _x Si exhibit a complex magnetic behavior for 0.6x1.75 involving ferromagnetic ordering followed by a reordering at lower temperature. Measurements of the thermal expansion and the specific heat C _p show only a weak anomaly at the Curie temperature, T _C, whereas a large, relatively sharp peak occurs at the magnetic reordering temperature, T _R. Thermal expansion measurements for the Fe_2.2Mn_0.8Si compound made about T _R are indicative of long-range ordering that can be suppressed in an applied field of 0.4T. Magnetization measurements show that low fields, 1–2 mT, strongly influence the bulk magnetization. Irreversible magnetization behavior, similar to that in spin-glass systems, is displayed.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.     

Room Temperature Giant Hall Effect in (Ni61Fe39) x (Al2O3)1−x Percolating Nanogranular Films

A series of (Ni₆₁Fe₃₉) _x (Al₂O₃)_1−x films were prepared using the magnetron sputtering technique. The maximum of saturated Hall resistivity 4.06 μΩ⋅cm was observed in (Ni₆₁Fe₃₉)₆₀(Al₂O₃)₄₀ nanogranular film at room temperature, which was about two orders larger than that of pure ferromagnetic metallic films. For the first time, the composition in the atomic fraction at the quantum percolation threshold was accurately characterized by the Rutherford backscattering (RBS) channelling technique in order to substantiate the newly metal-insulator fraction of percolation threshold in the Giant Hall Effect. It also was identified from the TEM image of an as-deposited sample that this large enhancement of the Hall resistivity coefficient was interrelated with the percolation threshold. With a different annealing temperature (T _A ) up to 300 °C , the saturated Hall resistivity of (Ni₆₁Fe₃₉)₆₀(Al₂O₃)₄₀ granular film decreased only a little, which showed its good thermal stability for potential application.     

Effect of Ti on glass-forming ability and magnetic properties of Fe81Si4B12−x P2Cu1Ti x (x = 0–3) soft magnetic alloys

The effect of Ti substitution for B on the glass-forming ability, microstructure and soft magnetic properties of Fe₈₁Si₄B_12?x P₂Cu₁Ti _x (x = 0–3) alloy ribbons made by single roller melt spinning method were investigated. The experimental results demonstrate that proper doping of Ti effectively improves the glass-forming ability, widening the optimum annealing temperature range, decreasing the sensitivity of coercivity on annealing temperature, increasing the volume fraction of nanocrystalline α-Fe phase and suppressing the grain growth in this alloy system. For alloy ribbons Fe₈₁Si₄B_12?x P₂Cu₁Ti _x (x = 0.5–2.5) annealed at 475 °C for 5 min, the saturation magnetostriction λ _s and the magnetic flux density B ₈₀₀₀ gradually decrease with increasing x, while the coercivity H _c decreases with increasing x until x = 2.0 and then increases. Nanocrystalline alloy Fe₈₁Si₄B₁₀P₂Cu₁Ti₂ shows excellent magnetic properties with low λ _s of 7 ppm, low H _c of 7.5 A/m and high B ₈₀₀₀ of 1.73 T which is promising for the future industrial applications.     

Optical and electrical properties of Y3+ ion substituted orthorhombic mullite Y(x)Al(6−x) Si2O13 nanoparticles

Y³⁺ substituted mullite Y_(x)Al_(6?x)Si₂O₁₃ nanoparticles where x varied from 0.005 to 0.05 have been synthesized via co-precipitation technique. X-ray diffraction results revealed that orthorhombic mullite was the major phase in the samples of x = 0.0–0.025, whereas corundum α-Al₂O₃ was predominant at high Y³⁺-ion content of x = 0.05. Transmission electron microscope images showed orthorhombic-like structure for the pure sample. Meanwhile, the doped samples exhibited similar morphologies of larger particle sizes associated with small amount of glassy liquid phase. FT-IR spectrum evinced the formation of corundum particularly at high Y³⁺ ion content (5 %). The photoluminescence emission spectra were strongly affected by the Y³⁺ ion content. Moreover, mullite sample doped with 0.5 % Y³⁺ ion achieved the minimum electrical resistivity of 0.28 × 10⁹ Ω cm and the minimum dielectric loss value of 0.37 in the radiowave frequency region (10 MHz) as well as the minimum dielectric loss value of 0.41 in the microwave frequency region (1 GHz).     

Low-temperature formation mechanism of double oxides Fe x Zr(Ti)1−0.75x O2−δ prepared from alkoxides and acetylacetonates

As a result of titanium and zirconium alcoholates hydrolysis in the presence of dissolved Fe(acac)₃, amorphous iron-containing gels have been synthesized. Their heat treatment has led to polycrystalline double oxides Fe _x Zr_1–0.75x O_2– (C) and Fe _x Ti_1–0.75x O_2– (T) formation. It has been shown that oxides (C) and (T) are likely to be solid solutions with 0.01<x<0.17 and 0.01<x<0.14, respectively. On the basis of X-ray diffraction and extended X-ray absorption fine structure data, iron-zirconium and iron-titanium crystallite models for gels and oxides have been proposed. It has been found that the crystallization process does not lead to a significant change in interatomic distances typical for local structures detected in gels.     

Magnetic properties of (Fe1−x M x )7Se8

The temperature dependence of the magnetization of the quenched and slowly cooled samples of Fe₇Se₈ and (Fe_1–x M _x )₇Se₈ samples with M = cobalt and nickel and x=0.02, 0.05 and 0.08 are given. All the thermomagnetic curves obtained belong to the Weiss ferrimagnetic type. Discontinuities indicating a magnetic transformation to antiferromagnetic order were obtained for some samples. The magnetic moment at 0 and 78 K (M ₀ and M₇₈) dependence on nickel and cobalt concentrations are given. The temperature dependence of the reciprocal susceptibility in the paramagnetic range was studied, and the asymptotic Curie points are given. The values of the effective magnetic moment, _eff, and the number of unpaired electrons were calculated. The thermal variation of the electrical conductivity of the host material, Fe₇Se₈, is given.     

X-ray,electrical conductivity and infrared studies of the system Zn1−x CO x Mn1−x Fe x CrO4

The system Zn_1–x Co _x Mn_1–x Fe _x CrO₄ is tetragonal in the range 0.0x0.4 and cubic in the range 0.5x1. Electrical resistivity temperature behaviour obeys Wilson's law for all the compounds and thermoelectric coefficient values vary between 135 to 226V K^–1. All compounds exhibit P-type semiconductivity and possess low mobility values (10^–9 cm² V^–1 sec^–1). The infrared spectra show the presence of two strong absorption bands around 500 and 600 cm^–1. The probable ionic configuration for the system is suggested to be Zn _1–x ²⁺ Fe _x ^–y3+ -Co _x ²⁺ [Mn _1–x ³⁺ Fe _y ³⁺ CO _x ^–y2+ Cr³⁺]O₄.     

Low-temperature properties of pseudoternary R(Rh1−x Ir x )4B4 (R=Ho and Dy) systems

Pseudoternary Ho(Rh_1–x Ir_x)₄B₄ and Dy(Rh_1–x Ir_x)₄B₄ systems were investigated with respect to the interplay between superconductivity (SC) and long-range magnetic ordering by means of specific heat (C) and upper critical magnetic field (H _c2) measurements. For Ho(Rh_1–x Ir_x)₄B₄ withx0.2 and Dy(Rh_1–x Ir_x)₄B₄ withx0.15, ferromagnetic (FM) ordering, reminiscent of spin-1/2 mean-field theory, was observed. In particular, FM ordering in Ho(Rh_1–x Ir_x)₄B₄ with 0.07x0.2 was found to destroy SC at a second critical temperatureT _c2 below the superconducting transition temperatureT _c, and was accompanied by a spike-shaped feature inC atT _c2. Coexistence of antiferromagnetic (AFM) ordering with SC was observed in both systems for 0.2x0.7. The compounds withx0.5 exhibited Néel temperaturesT _N that were smaller thanT _c and enhanced values ofH _c2 belowT _N. TheT _c andT _N undergo an abrupt decrease and increase, respectively, nearx0.5, and then cross atx0.6, above whichT _N>T _c. For Ho(Rh_1–x Ir_x)₄B₄ with 0.275x0.4, two different AFM transitions were detected in a double-peak feature inC.     

Photoconductivity in single crystals of (TlGaSe2)1−x(TlInS2)x alloys (0−0.45 ≤ x ≤0.55-1)

The spectral distribution of the photoconductivity in (TlGaSe₂)_1−x(TlInS₂)_x single crystals has been studied at 77 K and 300 K. At O ≤ x ≤ 4, Eg is observed to vary linearly with x. Eg(x) deviates from linearity at x = 0.6. This deviation is attributed to the effect of disorder in the composition. Over the range 0.6 to 2.2 eV pronounced impurity photoconductivity is detected at 77 K and 300 K. Deep impurity levels and their neighbourhood in this alloy are established to preserve their positions with the variation in the composition. The analysis of the obtained results indicates that the impurity centres are mainly connected with the cation neighbourhood.     

Physical and electrical properties of MnO2-doped Pb(Zr x Ti1−x )O3 ceramics

The effects of composition on the physical property change in the phase coexistence region between the tetragonal and rhombohedral phases have been investigated as a function of zirconium concentration, x, for the MnO₂-doped Pb(Zr _x Ti_1–x )O₃ (0.40x0.60) ceramics. The relative amount of phase coexisting between the tetragonal and rhombohedral phases affects greatly both dielectric and piezoelectric properties as a function of zirconium concentration. However, there are no detectable changes between the apparent density and microstructure. Also, in the coexistence region, the relative amount of coexistence of the rhombohedral phase increases with MnO₂ addition. The inflection points of the dielectric constant shift to lower zirconium concentration in proportion to the MnO₂ addition, owing to the substitution effect on the PZT lattice site.     

Preparation and electrical properties of (1 − x)BiScO3 · xPbTiO3 ceramics with MnO2 and Ni2O3 additions

We report the preparation of ceramic samples of (1 ? x)BiScO₃ · xPbTiO₃ · yMO _z (M = Mn, Ni; 0.63 ≤ x ≤ 0.65; 0 ≤ y < 0.02) solid solutions with a tetragonally distorted perovskite structure, X-ray diffraction characterization of the solid solutions, and their dielectric, piezoelectric, and pyroelectric properties. We present data on the symmetry and unit-cell parameters of the solid solutions, characteristics of their dielectric hysteresis loops, and the temperature dependences of their relative dielectric permittivity ?, dielectric loss tangent tan δ, piezoelectric charge coefficient d ₃₃, and pyroelectric coefficient p ^σ in the range 290–800 K. After poling, the ceramics possessed well-defined piezo- and pyroelectric properties, with characteristic 290-K d ₃₃ and p ^σ values of 300 pC/N and 15 nC/(cm² K), respectively.     

Preparation of the single phase γ′-(Fe1−x Ni x )4N compounds (0 ≤x ≤ 0.6)

Single phase -Fe₄N type (Fe_1–xNi_x)₄N compounds (0 x 0.6 have been synthesized for the first time by controlled heat treatment of iron-nickel oxalates in a gaseous flow of NH₃ xand H₂. The preparation processes were investigated using differential scanning calorimetry (DSC), X-ray diffraction and Mössbauer spectroscopy. The results confirmed that annealing of oxalates in the NH₃ and H₂ atmosphere included the processes of dehydration, decomposition and reduction, nitrogenation and thermal decomposition of the nitrides. The decomposition and reduction occur simultaneously. The final products depend on the flow rate ratio of NH₃ H₂ and the annealing temperature. The formation conditions for the single phase -Fe₄N type (Fe_1–xNi_x)₄N compounds are related to the nickel concentration, with increasing nickel content, the nitrogenation temperature decreased, in contrast the flow rate ratio of NH₃ H₂ increased.     

Magnetic and Magnetocaloric Properties of Laves Phase Dy1−x Gd x (Co1−x Ni x )2 Solid Solutions

We report magnetic and magnetocaloric properties of the polycrystalline series of Dy_1?x Gd _x (Co_1?x Ni _x )₂ (x=0.1, 0.2, 0.3, 0.4 and 0.5) solid solutions. The samples were characterized by powder X-ray diffraction patterns taken at room temperature and revealed that all the Dy_1?x Gd _x (Co_1?x Ni _x )₂ solid solutions consist of the C15 cubic Laves phase MgCu₂ type structure and a small amount of DyCo₃ and Dy₂O₃ impurity phases. Magnetic measurements showed that the samples undergoes a second-order type phase transition at T _C<130 K, from paramagnetic to ferromagnetic state. Heat capacity measurements have been performed for all solid solutions and allowed us to determine the Debye temperature. The magnetocaloric effect has been studied by means of specific heat measurements in magnetic field 0.42, 1 and 2 T. The GdNi₂ substitution effect on magnetic and magnetocaloric properties will be discussed.     

Magnetic characterization of Zr(Cr1−x Cu x )2 alloys and their hydrides

Magnetization measurements were carried out on the alloys Zr(Cr_1–x Cu _x )₂ (x=0, 0.1, 0.3, 0.5) before and after hydrogenation. All the binary and the ternary alloys, as well as their hydrides, exhibit a temperature-independent or nearly temperature-independent Pauli type of paramagnetism. Beside the Pauli paramagnetism, a ferromagnetic contribution to the total magnetization was observed for most of the alloys and their hydrides. It was also observed that hydrogen absorption enhances the Pauli paramagnetism as well as the ferromagnetism of the alloys. The rather unusual magnetic behaviour of these systems is briefly discussed in terms of 3d band filling of the transition metal, and is compared with some related systems.     

Effect of Fe and Co doping on electrical and thermal properties of La0.5Ce0.5Mn1−x(Fe,Co)xO3 manganites

The effect of Fe and Co doping on structural, electrical and thermal properties of half doped La_0.5Ce_0.5Mn_1−x(Fe, Co)_xO₃ is investigated. The structure of these crystallizes in to orthorhombically distorted perovskite structure. The electrical resistivity of La_0.5Ce_0.5MnO₃ exhibits metal-semiconductor transition (T_MS at ∼225 K). However, La_0.5Ce_0.5Mn_1−xTM_xO₃ (TM = Fe, Co; 0.0 ≤ x ≤ 0.1) manganites show semiconducting behavior. The thermopower measurements infer hole as charge carriers and electron–magnon as well spin wave fluctuation mechanism are effective at low temperature domain and SPC model fits the observed data at high temperature. The magnetic susceptibility measurement confirms a transition from paramagnetic to ferromagnetic phase. The observed peaks in the specific heat measurements, shifts to lower temperatures and becomes progressively broader with doping of transition metals on Mn-site. The thermal conductivity is measured in the temperature range of 10–350 K with a magnitude in between 10 and 80 mW/cm K.     

Synthesis,phase confirmation and electrical properties of (1 − x)KNNS−xBNZSH lead-free ceramics

Journal of Materials Science: Materials in Electronics - In the present work, lead-free piezoelectric ceramics (Rx)(K0.5Na0.5)(Nb0.96Sb0.04O3)?x(Bi0.5Na0.5)(Zr0.8Sn0.1Hf0.1)O3 [abb. as...