Effect of Ni Doping at Pd Site in Nb<Subscript>2</Subscript>PdS<Subscript>5</Subscript> Superconductor

The superconducting properties of Nb₂PdS₅ superconductor have been investigated with Ni doping at Pd site All the bulk polycrystalline Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.10) samples are crystallized in singlephase monoclinic structure. The electrical resistivity and magnetic measurements of Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.15) were carried out to study the variation of superconducting critical parameters with Ni doping. Superconductivity in Nb₂PdS₅ sample completely disappears for x ≥ 0.15. We observed that the ratio of upper critical field to transition temperature decreases with increasing Ni concentration. Also, the magnetization study of Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.15) samples shows similar superconducting behaviour. In summary, the superconductivity in Nb₂PdS₅ sample is slightly varying with partial doping of Ni at Pd site in Nb₂PdS₅ superconductor.     

Reactions of V<Subscript>2</Subscript>O<Subscript>5</Subscript>, Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>, and Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> with AlN

Reactions of vanadium, niobium, and tantalum pentoxides with aluminum nitride have been studied using X-ray diffraction. At temperatures from 1000 to 1600°C, we have identified various V, Nb, and Ta nitrides. The composition of the niobium and tantalum nitrides depends on the reaction temperature. The tendency toward nitride formation becomes stronger in the order V₂O₅ < Ta₂O₅ < Nb₂O₅.     

Synthesis of anisometric KSr<Subscript>2</Subscript>Nb<Subscript>5</Subscript>O<Subscript>15</Subscript> particles in the SrNb<Subscript>2</Subscript>O<Subscript>6</Subscript>–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–KCl system

Anisometric and agglomerate-free template particles are important for fabrication of grain-oriented ceramics. In the present work, preparation of acicular KSr₂Nb₅O₁₅ (KSN) particles was firstly explored in the SrNb₂O₆–Nb₂O₅–KCl system by molten salt synthesis (MSS) method. It was found that the molar ratio of SrNb₂O₆ to Nb₂O₅, the amount of KCl salt and synthesis time could significantly affect the phase structure and morphology of KSN particles. When calcined at 1,150 °C for 6 h with the molar ratio of SrNb₂O₆ to Nb₂O₅ was 1 and the weight ratio of salt to oxide source was 1.50, pure KSN particles with well-developed acicular morphology were successfully obtained in this system. They were agglomerate-free and with proper scale in the size range of 5–30 μm, which made them the ideal templates for fabricating textured ceramics. In addition, some new reaction and growth mechanisms were proposed in this work.     

Electrical Properties of the Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-NiO System

The electrical resistivity of Nb₂O₅-NiO materials was measured in the range 20-500°C. The resistivity of the samples was found to be sensitive to the presence of ammonia or sulfur dioxide in air. Some of the oxides in the Nb₂O₅-NiO system are potentially attractive as materials for temperature and gas sensors.     

Superconductivity at 5.5 K in Nb<Subscript>2</Subscript>PdSe<Subscript>5</Subscript> Compound

We report superconductivity in as-synthesized Nb₂PdSe₅, which is similar to a recently discovered Nb₂PdS₅ compound having very high upper critical field, clearly above the Pauli paramagnetic limit Zhang et al. (Sci. Rep. 3:1446, 2013). A bulk polycrystalline Nb₂PdSe₅ sample is synthesized by a solid-state reaction route in a phase-pure structure. The structural characterization has been done by X-ray diffraction, followed by Rietveld refinements, which revealed that the Nb₂PdSe₅ sample is crystallized in a monoclinic structure within the space group C2/m. Structural analysis revealed the formation of sharing of one-dimensional PdSe₂ chains. Electrical and magnetic measurements confirmed the superconductivity in Nb₂PdSe₅ compound at 5.5 K. Detailed magneto-resistance results exhibited the value of upper critical field to be around 8.2 T. The estimated H _c2(0) is within the Pauli paramagnetic limit, which is unlike the Nb₂PdS₅.     

Growth of ultrathin Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> films on quartz substrates

Niobium oxide films have been grown by reactive rf sputtering in a vacuum system and characterized by absorption spectroscopy and X-ray diffraction. The thickness of the (optically transparent) films has been determined as a function of sputtering time by examining interference effects in a plane-parallel layer. The average deposition rate is determined to be 7.4 ± 0.3 Å/min (95% confidence interval).     

Study of surface morphology and optical properties of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films with annealing

Nb₂O₅ films have been deposited on variety of substrates using the sol-gel dip coating technique. As-deposited films on all substrates are amorphous. Films were annealed under controlled ambience at 300, 400 and 600°C for 5 h. As-deposited films on glass substrate show uniform surface structure. The crystal structure and surface topography are found to depend strongly on the annealing temperature and nature of the substrates. The average grain size of 40 nm is observed in films annealed at 300°C. On annealing at 400°C increasing grain size and resulting fusing of them, enhanced surface roughness. Films deposited on NaCl substrates crystallized into a stable monoclinic phase and those deposited on single crystal Si substrates crystallized into hexagonal phase after annealing at 600°C. The as-deposited films show very high transmittance (>90%) in the visible region. The optical band gap is observed to increase from 4.35 eV when the films are in amorphous state to 4.87 eV on crystallization.     

Effect of ultrarapid quenching on the structure and mechanical properties of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> and Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

We have studied the detailed structure and mechanical properties of the Nb₂O₅ and Ta₂O₅ pentoxides after ultrarapid quenching in comparison with the properties of Nb₂O₅ and Ta₂O₅ ceramics prepared by a conventional ceramic processing technique and using high-intensity light (HIL) in an optical furnace. The results demonstrate that high-energy processing (HIL and ultrarapid quenching) improves the hardness and strength of Nb₂O₅ and Ta₂O₅. At the same time, HIL processing and quenching lead to structural disordering of the Nb₂O₅ and Ta₂O₅ pentoxides.     

Addition of Sb<Subscript>2</Subscript>O<Subscript>5</Subscript> into MgB<Subscript>2</Subscript> Superconductor Obtained by Spark Plasma Sintering

High-density (92–98 % of the theoretical density) MgB ₂ samples added with Sb ₂ O ₅ ((MgB ₂)+ (Sb ₂ O ₅) _x ,x= 0, 0.0025, 0.005, 0.015) were obtained by Spark Plasma Sintering. A higher amount of additive decreases density. In added samples, grains of secondary phases are located at MgB ₂ grain boundaries and they are of large size. Hence, Sb ₂ O ₅ does not promote effective flux pinning, connectivity is lower, and this suppresses the critical current density and the irreversibility field. Pinning force-related parameters indicate that added samples are close to the point pinning region and they show a higher grain boundary pinning contribution when compared with pristine MgB ₂ sample and when temperature is lower. It is speculated that for fixed processing conditions and Sb-oxide phases, a lower stability of the additive, reflected by a lower melting temperature, may promote reactive processes to start earlier leading to coarsening of the grains belonging to secondary phases.     

Effect of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> additions on the power loss of NiZn ferrites

Nickel–zinc ferrite system, Ni_0.65Zn_0.35Fe₂O₄ + x Nb₂O₅ where x varies from 0.0 wt% to 1.5 wt% in steps of 0.3 wt%, has been prepared by conventional ceramic technique. The samples were sintered at 1250 °C for 4 h in air atmosphere followed by natural cooling. The power loss and microstructures of these materials are examined. Microstructures reveal that niobium oxide additions promoted grain growth with an increase in grain size from 4 μm to 13.2 μm with the increase in niobium concentration. The measured power loss at frequencies from 100 kHz to 10 MHz under different exciting flux densities from 5 mT to 30 mT was found to be low up to 3 MHz, thus making the materials suitable for power applications up to this frequency. In the total power loss, hysteresis loss is predominant below 500 kHz and eddy current loss component is much higher at higher frequencies.     

Effect of high-intensity light on the properties and structure of ceramic Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>

This paper examines the effect of exposure to high-intensity light on the structure, thermal expansion, mechanical properties, and Raman spectrum of ceramic Nb₂O₅. We demonstrate that such exposure creates fractal micro- and nanostructures in ceramic Nb₂O₅, has a significant effect on its thermal expansion, increases its elastic moduli and the anisotropy in its mechanical properties, and produces isolated polyhedra in its crystal structure.     

Structural and electrical properties of SiO<Subscript>2</Subscript>–Li<Subscript>2</Subscript>O–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> glass and glass-ceramics obtained by thermoelectric treatments

Glass and glass-ceramics with the molar composition of 60SiO₂–30Li₂O–10Nb₂O₅ (mole %) were studied. Ferroelectric lithium niobate (LiNbO₃) nanocrystals were precipitated in the glass matrix trough a thermal treatment, with and without the simultaneous application of an external electric field. The as-prepared sample, yellow and transparent, was heat-treated (HT) at 600 and 650 °C and thermoelectric treated (TET) at 600 °C. The applied electric fields were the following ones: (i) 5 × 10⁴ V/m; (ii) 1 × 10⁵ V/m. Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and dielectric spectroscopies were used to investigate the glass samples properties. The LiNbO₃ crystalline phase was detected in the 650 °C HT sample and in the 600 °C TET samples. The presence of an external electric field, during the heating process, promotes the glass crystallization at lower temperatures. In the TET samples, the surface crystallization of the cathode and the anode are different. The number and size of the crystallites, in the glass network, dominate the electrical dc behavior while the ac conductivity process is more dependent of the glass matrix structure. The obtained results reflect the important role carried out by the temperature and the applied electric field in the glass-ceramic structures.     

PTCR effect in BaBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>-doped BaTiO<Subscript>3</Subscript> ceramics

The influences of BaBi₂Nb₂O₉ content on the electrical property and the microstructure of BaTiO₃-based materials have been studied. With an increase in BaBi₂Nb₂O₉ content the grain size decreases. All the prepared BaBi₂Nb₂O₉ doping BaTiO₃-based thermistors show typical PTC effect. As the amount of BaBi₂Nb₂O₉ added in BaTiO₃-based ceramics increases, resistivity appears to exhibit a minimum value. At high BaBi₂Nb₂O₉ content (≥0.0875), the resistivity increased again with increasing BaBi₂Nb₂O₉ content. At a given content of BaBi₂Nb₂O₉, the influence of sintering temperature on the electrical properties of samples has been investigated. A minimum of room temperature resistivity is obtained at the sintering temperature equal to 1,290 °C at a given content of BaBi₂Nb₂O₉.     

Phase,microstructural characterization and dielectric properties of Ca-substituted Sr<Subscript>5</Subscript>Nb<Subscript>4</Subscript>TiO<Subscript>17</Subscript> ceramics

The effect of Ca substitution for Sr on the phase, microstructure and microwave dielectric properties of the Sr_5−x Ca _x Nb₄TiO₁₇ composition series was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), an LCR meter, and vector network analyzer. Below 1450 °C, Sr_5−x Ca _x Nb₄TiO₁₇ (x = 1, 2, 3, or 4) compositions formed single-phase Sr₄CaNb₄TiO₁₇, Sr₃Ca₂Nb₄TiO₁₇, Sr₂Ca₃Nb₄TiO₁₇, and SrCa₄Nb₄TiO₁₇ ceramics, respectively. At x = 0 and 5, Sr₅Nb₄TiO₁₇ and Ca₅Nb₄TiO₁₇ formed, but along with Sr₂Nb₂O₇ (at x = 0) and CaNbO₃ and CaNb₂O₆ (at x = 5) secondary phases. Above 1450 °C, all the compositions formed two-phase ceramics. At low frequencies, a phase transition was observed in the composition Sr₅Nb₄TiO₁₇. The substitution of Ca for Sr enabled processing of highly dense Sr₂Ca₃Nb₄TiO₁₇, with ε_r ~ 53.4, τ_f ~ −6.5 ppm/°C and Q _u  × f _o  ~ 1166 GHz. Further investigations are required to improve the quality factor of these ceramics for possible microwave applications.     

Solid-state synthesis,characterization, and properties of Ni<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>-based solid solutions

In this paper, we report the solid-state synthesis, characterization, and physicochemical properties of Ni_4–x Zn _x Nb₂O₉ (x = 0, 0.1, 0.3, 0.5, 0.75, 1.0) zinc-containing nickel niobates and Ni₄Nb_2–x Ta _x O₉ (x = 0.1, 0.3, 0.5, 1.0, 2.0) solid solutions. The materials were characterized by X-ray diffraction. We determined the particle size composition of the synthesized powders, assessed their chemical stability in acid media, obtained IR spectra of the solid solutions, and measured their electrical conductivity as a function of temperature. Some of the solid solutions were used to fabricate and characterize nickel-selective electrodes, which were successfully tested in ion-selective measurements.     

Preparation and characterization of new dielectric ceramics Ba<Subscript>5</Subscript>LnTi<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>18</Subscript> (Ln = La,Nd)

Two new A₆B₅O₁₈ type cation-deficient perovskites Ba₅LnTi₂Nb₃O₁₈ (Ln = La, Nd) were prepared by the conventional solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Both compounds crystallize in the trigonal system. Ba₅LaTi₂Nb₃O₁₈ has a dielectric constant of 56.6, a high quality factors (Q_u × f > 16,700 at 4.3331 GHz), and a relatively large temperature coefficient of resonant frequency (_f) + 142 ppm°C^–1 at room temperature; Ba₅NdTi₂Nb₃O₁₈ has a higher dielectric constant of 47.3 with high quality factors Q_u × f > 15,000 at 4.6830 GHz, and _f + 128 ppm°C^–1.     

Ag-decorated octahedral K<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> nanoparticles with enhanced photocatalytic performance

The Ag-K₂Nb₂O₆ nanocomposites are synthesized by a two-step method where the octahedral K₂Nb₂O₆ is initially prepared by solvothermal reaction and then the Ag particles are anchored onto the surface of K₂Nb₂O₆ through the photoreduction of AgNO₃. The XRD, SEM, TEM, XPS, DRS are applied to characterize the structure, morphology and optical properties, which confirm that the Ag particles are successfully deposited on the surface of K₂Nb₂O₆. Compared with the pure K₂Nb₂O₆, the Ag modified K₂Nb₂O₆ catalysts show an obvious enhancement catalysis under UV–Vis light, because that could efficiently promote the light absorption and the separation of photoelectrons and holes.     

Crystal structure and electrical properties of CaNaBi<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramics

Monophasic CaNaBi₂Nb₃O₁₂ powders were synthesized via the conventional solid-state reaction route. Rietveld refinement of the X-ray powder diffraction (XRD) data and selected area electron diffraction (SAED) studies confirmed the phase to be a three-layer Aurivillius oxide associated with an orthorhombic B2cb space group. The dielectric properties of the ceramics have been studied in the 300–800 K temperature range at various frequencies (1 kHz to 1 MHz). A dielectric anomaly was observed at 676 K for all the frequencies corresponding to the ferroelectric to paraelectric phase transition as it was also corroborated by the high temperature X-ray diffraction studies. The incidence of the polarization–electric field (P vs. E) hysteresis loop demonstrated CaNaBi₂Nb₃O₁₂ to be ferroelectric.     

X-ray diffraction study of the Cu<Subscript>2</Subscript>Se-In<Subscript>2</Subscript>Se<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>Se<Subscript>3</Subscript> system near CuInCr<Subscript>2</Subscript>Se<Subscript>5</Subscript>

The structure of three compounds in the Cu₂Se-In₂Se₃-Cr₂Se₃ system near CuInCr₂Se₅ is determined by single-crystal x-ray diffraction: CuInCr₄Se₈ (I), Cu₂In₂Se₄ (II), and Cu_0.5In_0.5Se (III). I has a cubic (spinel type) structure: a = 10.606(4) Å, Z = 4, sp. gr. F43m. II has a pseudotetragonal (sphalerite type) structure: a = 5.774(2) Å, c = 11.617(6) Å. The structure of II was solved in a reduced unit cell with a = 5.774(2) Å, b = 5.774(2) Å, c = 7.095(6) Å, = 113.95(5)°, = 113.95(5)°, = 90.00(4)°, Z = 1, sp. gr. P1. III has a triclinic cell (disordered structure of II): a = 4.088(1) Å, b = 4.091(2) Å, c = 4.101(1) Å, = 60.05(1)°, = 60.08(1)°, = 89.98(4)°, Z = 1, sp. gr. P1. The Cu and In atoms in I sit in inequivalent tetrahedral sites, and the Cr atoms reside in octahedral interstices of the close packing of Se atoms. The bond lengths are In–Se = 2.538(6), Cr(1)–Se(1) = 2.514(7), Cr(1)–Se(2) = 2.576(8), and Cu–Se = 2.437(5) Å. In II, all of the atoms sit in tetrahedral sites; the mean bond lengths are In–Se = 2.578(6) and Cu–Se = 2.44(1) Å. In III, the Cu and In atoms are fully disordered in the same tetrahedral site; the mean Cu(In)–Se bond length is 2.508(6) Å.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1435–1439.Original Russian Text Copyright © 2004 by Antsyshkina, Sadikov, Koneshova, Sergienko.