Influence of thickness on the material characteristics of reactively sputtered W2N layer and electrical properties of W/W2N/SiO2/Si capacitors

The material characteristics of W₂N layer and electrical properties of W/W₂N/SiO₂/Si metal–oxide–semiconductor (MOS) capacitors with different W₂N thickness upon annealing in N₂ + H₂ ambient at 500 °C for 20 min are investigated. The nitrogen concentration of W₂N for the W/W₂N stack with thin W₂N layer (≤10 nm) is lower than that for the W/W₂N stack with thick W₂N layer (≥15 nm). In addition, the crystallinity of W₂N in the W/W₂N (15 nm) stack is better than that in the W/W₂N (10 nm) stack. For all capacitors, the oxide charges decrease significantly after annealing and the amount of oxide charges is independent of the W₂N thickness. However, the work function (Φ_m) of the W/W₂N (≤10 nm) stack (4.6 eV) is smaller than that of W/W₂N (15 nm) stack (5.0 eV). The Φ_m of W/W₂N (15 nm) stack is close to that of W₂N single layer. After annealing, the Φ_m of W/W₂N (15 nm) stack and W₂N single layer decrease, especially for the W₂N single layer. But for the W/W₂N (≤10 nm) stack, the Φ_m increases after annealing.     

Magnetic properties of (Fe)1−x–(Al2O3)x and (Fe50Ni50)1−x–(Al2O3)x nanocomposite magnetic media synthesized using gel like Al2O3 matrix

Composites with ferromagnetic nanoparticles, Fe and Fe₅₀Ni₅₀, dispersed in Al₂O₃ have been synthesized by a solution phase technique. The structure and magnetic properties of these composites with varying fractions of Al₂O₃ have been investigated. Both Fe and Fe₅₀Ni₅₀ nanoparticles are amorphous in the as-prepared state and become crystalline on heat treating with near equilibrium lattice parameters of 0.287 nm and 0.358 nm respectively. The interparticle distance increases with increasing Al₂O₃ from 0 wt.% to 20 wt.%. The size of Fe nanoparticles is 40 nm while the Fe₅₀Ni₅₀ nanoparticles are 20 nm in size. The Fe and Fe₅₀Ni₅₀ nanoparticles dispersed composites are found to be ferromagnetic at room temperature both in the as-prepared and heat treated conditions with clear coercive fields of 5.5–35 × 10³ A m⁻¹. The saturation magnetization increases by orders of magnitude on heat treatment, for e.g. from <1.0 emu g⁻¹ to 143.4 emu g⁻¹ for Fe–15 wt.% Al₂O₃ and 95.6 emu g⁻¹ for Fe₅₀Ni₅₀–15 wt.% Al₂O₃. The Fe-composites exhibit a Curie transition at 1000 K while the Fe₅₀Ni₅₀ composites exhibit a transition at 880 K, both temperatures close to bulk values.     

Phase formation, microstructure and magnetic properties investigation in Cu and Fe substituted SmCo5 melt-spun ribbons

Magnetic properties and microstructure were investigated in Sm_17.24Co_66.20Cu_8.28Fe_8.28 ribbons melt-spun at different wheel speeds of 5, 15, 30, 40 and 50 m/s. X-ray diffraction studies revealed that the ribbons melt-spun at lower wheel speed (<15 m/s) were comprised of three phases viz. SmCo₇, Sm₂Co₇ and SmCo₅, while higher wheel speed ribbons exhibited single phase SmCo₅. The coercivity was found to increase with increase of the wheel speed. A high coercivity of 33 kOe was obtained in ribbon prepared at 50 m/s.     

Improved high-Q microwave dielectric resonator using ZnO-doped La(Co1/2Ti1/2)O3 ceramics

The microwave dielectric properties and the microstructures of ZnO-doped La(Co_1/2Ti_1/2)O₃ ceramics prepared by conventional solid-state route have been studied. Doped with ZnO (up to 0.75 wt%) can effectively promote the densification of La(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. At 1320 °C, La(Co_1/2Ti_1/2)O₃ ceramics with 0.75 wt% ZnO addition possesses a dielectric constant (_r) of 30.2, a Q × f value of 73,000 GHz (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −35 ppm/°C.     

dc-Magnetic susceptibility and EPR studies of vapour phase grown Cd1−xCoxTe crystals

Cd_1−xCo_xTe crystals (x = 0.001, 0.003, 0.005, 0.007 and 0.009) were grown by vapour phase technique. The grown diluted magnetic semiconducting (DMS) crystals were subjected to magnetization and dc-magnetic susceptibilities at room temperature. EPR spectra were recorded at 20 K for samples of all compositions. EPR spectra exhibited a broad resonance band around g  5.43. All the studies indicated the paramagnetic nature of the samples.     

Complete flux jumping in nano-structured MgB2 superconductors prepared by mechanical alloying

High density nano-crystalline MgB₂ bulk superconductors with induced pinning centres were prepared from elemental precursors by a sequence of ball milling, heat treatment, and final pressing. The XRD results revealed the main phase was MgB₂ with a minor component of MgO. The magnetic moment versus temperature indicated that the transition temperature of MgB₂ samples was around 34 K, which is less than the typical transition temperature of commercial powders and also the transition temperature strongly depended on the milling time. It is well known that introduction of defects, grain boundaries and impurities act as effective flux pinning centres in MgB₂ and results in increased critical current density, J_c and decreased the transition temperature, T_c. The magnetization measurements were performed using VSM at 10 K, 20 K and 30 K, and the M–H curves indicated a complete flux jump effect, which is a severe problem for the application of superconductors. It was determined that a noticeable amount of heating (0.3 K jumps at 10 K) occurs at these jumps. In addition, it was found that the sweeping rate of magnetic field and the size of bulk sample are very effective to promote the flux jumping and whereas a low sweeping rate (12 Oe/s) avoids these “avalanches”, consistent with a kind of supercritical phenomenon: going slower allows the field gradients to stay close enough to equilibrium so that the avalanche effect is not triggered. In contrast, the sweeping rate of 100 Oe/s leads to numerous jumps.     

Micro-forming of Zr65Al10Ni10Cu15 metallic glasses under superplastic condition

Micro-formability behavior of the Zr₆₅Al₁₀Ni₁₀Cu₁₅ alloy sheet fabricated by using squeeze casting method, which exhibited Newtonian behavior in the supercooled liquid region, was examined by finite element methods and experiments. In micro-forming simulation on a single V-groove, micro-formability index increased with time and nearly completed die-filling was achieved in 100 s when deformed under a constant pressure of 52.6 MPa at 696 K. In micro-forming on the die with multiple V-grooves in array along its width, the degree of die-filling was predicted to depend on the V-groove position. The V-grooves near the center of the die exhibited the high degree filling ratio of 1 but it was only 0.1 near the free end. This trend was confirmed to agree with the experimental results. According to the simulation result, higher friction coefficient and longer loading time could improve the die-filling ability near the free end.     

Si-induced superconductivity and structural transformations in DyRh4B4

DyRh₄B₄ has been known to crystallize in the primitive tetragonal (pt)-structure and to exhibit a ferromagnetic transition at 12 K, the highest magnetic transition temperature in the entire series of the RRh₄B₄ materials [For an extensive review on the magnetic and superconducting properties on the ternary superconductors, including RRh₄B₄, see, for example, Ø. Fischer, in: K.H.J. Buschow, E.P. Wohlfarth (Eds.), Ferromagnetic Materials, vol. 5, Elsevier Science Publishers B.V., 1990 (Chapter 6)]. We show here that our silicon-added samples of the nominal composition DyRh₄B₄Si_0.2 exhibit superconductivity below T_c  4.5 K and an antiferromagnetic transition below T_N  2.7 K. The 12 K transition observed in the pt-DyRh₄B₄ is completely suppressed. Our annealed samples mainly consist of domains of the chemical composition DyRh_3.9B_4.2Si_0.08. These domains contain two crystallographic phases belonging to the body-centred tetragonal (bct)-structure and the orthorhombic (o)-structure. We have reasons to suggest that superconductivity and antiferromagnetic ordering arise from bct-DyRh₄B₄ phase and, therefore, coexist below T_N  2.7 K.     

Synthesis and crystal structure of a new calcium borate, CaB6O10

A new calcium borate, CaB₆O₁₀, has been prepared by solid-state reactions at temperature below 750 °C. The single-crystal X-ray structural analysis showed that CaB₆O₁₀ crystallizes in the monoclinic space group P2₁/c with a = 9.799(1) Å, b = 8.705(1) Å, c = 9.067(1) Å, β = 116.65(1)°, Z = 4. It represents a new structure type in which two [B₃O₇]⁵⁻ triborate groups are bridged by one oxygen atom to form a [B₆O₁₃]⁸⁻ group that is further condensed into a 3D network, with the shorthand notation 6: ∞³[2 × (3:2Δ + T)]. The 3D network affords intersecting open channels running parallel to three crystallographically axis directions, where Ca²⁺ cations reside. The IR spectrum further confirms the presence of both BO₃ and BO₄ groups.     

Thermoelectric properties of novel skutterudites with didymium: DDy(Fe1−xCox)4Sb12 and DDy(Fe1−xNix)4Sb12

In order to improve the thermoelectric properties via efficient phonon scattering Didymium (DD), a mixture of Pr and Nd, was used as a new filler in ternary skutterudites (Fe_1−xCo_x)₄Sb₁₂ and (Fe_1−xNi_x)₄Sb₁₂. DD-filling levels have been determined from combined data of X-ray powder diffraction and electron microprobe analyses (EMPA). Thermoelectric properties have been characterized by measurements of electrical resistivity, thermopower and thermal conductivity in the temperature range from 4.3 to 800 K. The effect of nanostructuring in DD_0.4Fe₂Co₂Sb₁₂ was elucidated from a comparison of both micro-powder (ground in a WC-mortar, 10 μm) and nano-powder (ball-milled, 150 nm), both hot pressed under identical conditions. The figure of merit ZT depends on the Fe/Co and Ni/Co-contents, respectively, reaching ZT > 1. At low temperatures the nanostructured material exhibits a higher thermoelectric figure of merit. The Vickers hardness was measured for all samples being higher for the nanostructured material.     

CTAB-assisted hydrothermal synthesis of NiFe2O4 and its magnetic characterization

A simple hydrothermal route is demonstrated for the synthesis of nickel ferrite nanocrystals, NiFe₂O₄, using cetyltrimethylammonium bromide (CTAB) as the surfactant and NH₃ and NaOH as hydrolyzing agents. Synthesized materials have been characterized by XRD, FTIR, ESR, and TEM techniques. It was found that crystallization in both hydrolyzing agent led to nanometric in size. Average particle size of prepared samples was calculated from TEM micrographs and varied significantly between samples prepared using different hydrolyzing agents; it was 12 nm when conc. NH₃ was used and 50 nm when 2 M NaOH was used. Crystallite size obtained using Scherrer equation agreed well with the TEM observations with the respective values of 15 and 55 nm. ESR analysis showed single broad bands which might indicate the phase homogeneity of the materials. Furthermore, linewidths were observed to differ due to the difference in magnetization that depends on the particle size; NiFe₂O₄ sample hydrolysed with NH₃ has a larger linewidth revealing its smaller particle size as confirmed by XRD and TEM techniques.     

Milling and subsequent thermal annealing effects on the microstructural and magnetic properties of nanostructured Fe90Co10 and Fe65Co35 powders

The influence of milling and subsequent annealing on the microstructural and magnetic properties of Fe₉₀Co₁₀ and Fe₆₅Co₃₅ alloys is investigated. After milling for 8 h a body-centred cubic nanostructured Fe–Co alloy forms with an average crystallite size of about 12 nm. The magnetization saturation (M_S) increases 16% for Fe₆₅Co₃₅ and 5% for Fe₉₀Co₁₀ alloys by milling for 8 h. Subsequent annealing of Fe₉₀Co₁₀ and Fe₆₅Co₃₅ powders for 105 min at 550 °C improves the M_S about 6 and 11%, respectively. Before annealing, the coercivity increases (up to 60 Oe) by milling for 3 h, followed by a reduction on milling for longer periods (45 h). At the initial stage of the heating, a sharp decrease in H_C to 8–10 Oe occurs due to the relief of internal strain. Further heating leads to an increase in the coercivity (intermediate times) followed by a slight diminution on heating for final stage.     

Subsolidus phase relationships in the system ZnO–Li2O–WO3

The subsolidus phase relationships of the system ZnO–Li₂O–WO₃ have been investigated by X-ray diffraction (XRD) analyses. There are one ternary compound, five binary compounds and eight 3-phase regions in this system. The new ternary compound Li₂Zn₂W₂O₉ was found by the powder diffraction pattern. The corresponding crystal structure of this compound was refined by Rietveld profile fitting method. It belongs to a trigonal system with space group and lattice constants are a = 5.1438(2) Å, c = 14.1052(3) Å, and its thermal property was studied.     

Conductivity of a new pyrophosphate Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous solution method

New pyrophosphate Sn_0.9Sc_0.1(P₂O₇)_1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ have been investigated. XRD analysis indicates that Sn_0.9Sc_0.1(P₂O₇)_1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn_0.9Sc_0.1(P₂O₇)_1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ in open air is 2.35 × 10⁻⁶ and 2.82 × 10⁻⁹ S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10⁻⁷ S/cm at 400 °C) than in open air indicating some proton conduction. SnP₂O₇ and Sn_0.92In_0.08(P₂O₇)_1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP₂O₇-based materials might be related to the synthetic history. The possible conduction mechanism of SnP₂O₇-based materials has been discussed in detail.     

Investigation of the microwave dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics for application in coplanar patch antenna

In this paper, the dielectric properties of Ca_1−xMg_xLa₄Ti₅O₁₇ ceramics at microwave frequency have been studied. The diffraction peaks of Ca_(1−x)Mg_xLa₄Ti₅O₁₇ ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm³ can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (_r) and quality factor (Q × f) of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τ_f) of −9.6 ppm/°C can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved.     

Growth of Mn, Co and Ni-doped near-stoichiometric LiNbO3 by Bridgman method using K2O flux

The near-stoichiometric LiNbO₃ (SLN) single crystals doped Mn²⁺, Co²⁺ and Ni²⁺ in 0.5 mol% concentration in the raw compositions were grown by the Bridgman method under the conditions of taking K₂O as flux, a high temperature gradient (90–100 °C/cm) for solid–liquid interface. The XRD, absorption spectra, excitation spectra and emission spectra have been carried out. From the absorption edges of Mn²⁺, Co²⁺ and Ni²⁺-doped SLN crystals, the molar ratio of [Li⁺]/[Nb⁵⁺] are estimated to be about 0.977. The absorption spectra of Mn²⁺:SLN have shown a broad absorption band centered at 571 nm (⁶A_1g(⁶S) → ⁴T_1g(⁴G)), three absorption peaks at 520, 549 and 612 nm (overlapping of the ⁴T₁(F)–⁴A₂(F), ⁴T₁(F)–⁴T₁(P)), and a wide absorption band at 1400 nm (⁴T₁(F) → ⁴T₂(F)) of Co²⁺:SLN, Ni²⁺:SLN, and five absorption peaks at 381 nm (³A_2g(F) → ³T_1g(P)), 733 nm (³A_2g(F) → ³T_1g(F)), 1280 nm (³A_2g(F) → ³T_2g(F)), 430 nm (³A_2g(F) → ¹T_2g(D)), and 840 nm (³A_2g(F) → ¹E(D)) of Ni²⁺:SLN were observed. A red emission at 612 nm (⁴T_1g(⁴G) → ⁶A_1g(⁶S)) for Mn²⁺:SLN, a red emission at 775 nm (⁴T₁(P) → ⁴T₁(F)) for Co²⁺:SLN, and a green emission at 577 nm (¹T_2g(D) → ³A_2g(F)) and a red emission at 820 nm (¹T_2g(D) → ³T_2g(F)) for Ni²⁺:SLN were observed under excited by 416, 520 and 550 nm lights, respectively. The concentration distribution of Mn²⁺, Co²⁺and Ni²⁺ ion in SLN crystals was investigated primarily from the absorption and emission spectra for various parts. The effective distribution coefficient for Mn²⁺ was less than 1. While, for Co²⁺ and Ni²⁺ were more than 1.     

Role of titanium valence states in optical and electronic features of PbO–Sb2O3–B2O3:TiO2 glass alloys

PbO–Sb₂O₃–B₂O₃ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 1.5 mol.%) were synthesized. The samples are characterized by X-ray diffraction, scanning electron microscopy and DSC techniques. A variety of properties, i.e. optical absorption, photoluminescence, infrared, ESR spectra, magnetic susceptibility, photo-induced birefringence (PIB) and dielectric properties (constant ′, loss tan δ, a.c. conductivity σ_ac over a wide range of frequency and temperature) of these glass–ceramics have been explored. The analysis of these results indicated that Ti ion surrounding ligands play principal role in the observed PIB and the sample crystallized with 0.8 mol.% of TiO₂ is the most suitable for the applications in non-linear optical devices.     

The influence of Zn-dopant on the precipitation of α-FeOOH in highly alkaline media

The influence of Zn-dopant on the precipitation of α-FeOOH in highly alkaline media was monitored by X-ray diffraction (XRD), ⁵⁷Fe Mössbauer and Fourier transform infrared (FT-IR) spectroscopies and field emission scanning electron microscopy (FE SEM). Acicular and monodisperse α-FeOOH particles were precipitated at a very high pH by adding a tetramethylammonium hydroxide solution to an aqueous solution of FeCl₃. The XRD analysis of the samples precipitated in the presence of Zn²⁺ ions showed the formation of solid solutions of α-(Fe, Zn)OOH up to a concentration ratio r = [Zn]/([Zn] + [Fe]) = 0.0909. ZnFe₂O₄ was additionally formed in the precipitate for r = 0.1111, whereas the three phases α-FeOOH, α-Fe₂O₃ and ZnFe₂O₄ were formed for r = 0.1304. In the corresponding FT-IR spectra, the FeOH and FeO stretching bands were sensitive to the Zn²⁺ substitution, whereas the FeOH bending bands of α-FeOOH at 892 and 796 cm⁻¹ were almost insensitive. The Mössbauer spectra showed a high sensitivity to the formation of α-(Fe, Zn)OOH solid solutions which were monitored on the basis of a decrease in B_hf values in dependence on Zn-doping. A strictly linear decrease in B_hf for α-FeOOH doped with Zn²⁺ ions was measured up to r = 0.0291, whereas for r = 0.0476 and higher there was a deviation from linearity. The presence of α-(Fe, Zn)OOH, α-Fe₂O₃ and ZnFe₂O₄ phases in the samples was determined quantitatively by Mössbauer spectroscopy. Likewise, Mössbauer spectroscopy did not show any formation of the solid solutions of α-Fe₂O₃ with Zn²⁺ ions. FE SEM showed a strong effect of Zn-doping on the elongation of acicular α-FeOOH particles (500–700 nm in length) up to r = 0.1111. For r = 0.1304 the sizes of ZnFe₂O₄ particles were around 30–50 nm, and those of α-Fe₂O₃ particles were around 500 nm, whereas a relatively small number of very elongated α-(Fe, Zn)OOH particles was observed. A possible mechanism of the formation of α-(Fe, Zn)OOH, α-Fe₂O₃ and ZnFe₂O₄ particles was suggested.     

Transport anisotropy and pseudo-gap state in oxygen deficient ReBa2Cu3O7−δ (Re = Y, Ho) single crystals

The temperature dependence of the transport anisotropy of ReBa₂Cu₃O_7−δ (Re = Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δ_c increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa₂Cu₃O_7−δ, the temperature dependence of the anisotropy of the resistivity ρ_c/ρ_ab(T) for the HoBa₂Cu₃O_7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity.