Microwave dielectric properties of Ba<Subscript>4</Subscript>LaTiNb<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Ta<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>15</Subscript> ceramics

High dielectric constant and low loss ceramics in the system Ba₄LaTiNb_3−x Ta _x O₁₅ (x = 0–3) have been prepared by conventional solid-state ceramic route. Ba₄LaTiNb_3−x Ta _x O₁₅ solid solutions adopted A₅B₄O₁₅ cation-deficient hexagonal perovskite structure for all compositions. The materials were characterized at microwave frequencies. They show a linear variation of dielectric properties with the value of x. Their dielectric constant varies from 53.1 to 42.3, quality factor Q_u × f from 18,790 to 28,070 GHz and temperature variation of resonant frequency from +94.3 to +33.1 ppm/°C as the value of x increases.     

Synthesis and properties of columbite-structure Mg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Nb<Subscript>2</Subscript>O<Subscript>6 − <Emphasis Type="Italic">x</Emphasis></Subscript>

The formation of the columbite-structure magnesium niobate MgNb₂O₆ is a multistep process. Single-phase material can only be obtained through long-term high-temperature heat treatment. Deviations from stoichiometry have a significant effect on the microwave quality factor Q of the material: magnesium-deficient ceramics contain small amounts of Nb₂O₅ and have relatively low Q values, whereas an excess of magnesium leads to the formation of Mg₄Nb₂O₉ (alpha-alumina structure) as an impurity phase, thereby drastically increasing the electrical Q.     

Microstructures and multiferroic properties of YFe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> ceramics prepared by spark plasma sintering

YFe_1−x Mn _x O₃ (x = 0.1, 0.2, and 0.4) dense ceramics were prepared by SPS (spark plasma sintering). The dielectric characteristics were evaluated over broad temperature and frequency ranges, and an obvious dielectric relaxation was observed. It was a thermally activated process following the Arrhenius law, and the activated energy decreased with increasing Mn-content. Obvious ferroelectric hysteresis loops were observed at 153 and 123 K for different compositions. The weak ferromagnetic characteristics were detected at room temperature for all compositions, and the remnant magnetization was reduced with increasing Mn-content. These results indicated the multiferroic properties in the Mn-substituted YFeO₃ ceramics.     

Crystal Structure of Nb<Subscript>5</Subscript>Si<Subscript>3 − <Emphasis Type="Italic">x</Emphasis></Subscript>P<Subscript>0.5 + <Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0–0.5)

The structure of the ternary compound Nb₅Si_{3 ? x}P_{0.5 + x} (x = 0–0.5) is determined by single-crystal x-ray diffraction: sp. gr. P6₃mc, a = 1.32350(5) nm, c = 0.52954(1) nm; R _F = 0.028, R_w = 0.081 for 547 reflections with F _hkl > 4.0σ(F _hkl ). Relations between the structure of Nb₅Si_{3 ? x}P_{5 + x}, the Mn₅Si₃ structure type, and its derivatives are discussed.     

Low-temperature heat capacity of Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> solid solutions

The heat capacity of Li _x Ni_{2 − x} O₂ (x = 0.40–0.76) oxides has been measured using an adiabatic calorimeter, and their thermodynamic functions have been determined. The results indicate that the lithium nickelate solid-solution series contains a two-phase region and that near-stoichiometric LiNiO₂ has a layered structure, in accordance with earlier results.     

Microstructure and microwave dielectric properties of (Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>SiO<Subscript>4</Subscript> ceramics

(ZnMg)₂SiO₄ powders was prepared by the sol-gel process, and the microstructure and dielectric properties of (Zn_1−xMg_x)₂SiO₄ microwave materials were investigated systematically. TG-DSC and XRD analyzes for gels indicate that the (ZnMg)₂SiO₄ with pure willemite phase could be obtained at low temperature of 850°C. Further, XRD illustrates that just small amounts of Mg can be incorporated into Zn₂SiO₄ lattice, and the solid solution limit of Mg in Zn₂SiO₄ is about x = 0·1. By appropriate Mg substitution for Zn, the sintering range is widened and the sintering temperature of Zn₂SiO₄ ceramics can be lowered effectively. SEM shows that Mg-substitution for Zn can promote the grain growth of Zn₂SiO₄. Moreover, the microwave dielectric properties strongly depended on the substitution content of Mg and sintering temperatures. (Zn_0·8Mg_0·2)₂SiO₄ dielectrics sintered at 1170°C show the condense microstructure with small uniform grains and best microwave properties: ɛ _r = 6·3, Q × f = 189800 GHz and τ _f = −63 ppm/°C.     

Heat capacity of Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> solid solutions

We have synthesized Li _x Ni_{2 − x} O₂ oxides in the range x = 0.1–0.84 and showed that the solid-solution system contains a two-phase region. The heat capacity of Li _x Ni_{2 − x} O₂ has been determined by differential scanning calorimetry.     

Towards high-mobility In<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>2–2<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> nanowire field-effect transistors

Recently, owing to the excellent electrical and optical properties, n-type In₂O₃ nanowires (NWs) have attracted tremendous attention for application in memory devices, solar cells, and ultra-violet photodetectors. However, the relatively low electron mobility of In₂O₃ NWs grown by chemical vapor deposition (CVD) has limited their further utilization. In this study, utilizing in-situ Ga alloying, highly crystalline, uniform, and thin In_2xGa_2?2xO₃ NWs with diameters down to 30 nm were successfully prepared via ambient-pressure CVD. Introducing an optimal amount of Ga (10 at.%) into the In₂O₃ lattice was found to effectively enhance the crystal quality and reduce the number of oxygen vacancies in the NWs. A further increase in the Ga concentration adversely induced the formation of a resistive β-Ga₂O₃ phase, thereby deteriorating the electrical properties of the NWs. Importantly, when configured into global back-gated NW field-effect transistors, the optimized In_1.8Ga_0.2O₃ NWs exhibit significantly enhanced electron mobility reaching up to 750 cm²·V^–1·s^–1 as compared with that of the pure In₂O₃ NW, which can be attributed to the reduction in the number of oxygen vacancies and ionized impurity scattering centers. Highly ordered NW parallel arrayed devices were also fabricated to demonstrate the versatility and potency of these NWs for next-generation, large-scale, and high-performance nanoelectronics, sensors, etc.

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Thermoelectric properties of perovskite oxides La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoO<Subscript>3</Subscript> prepared by polymerlized complex method

P-type perovskite oxides La_1−x Sr _x CoO₃ (0 ≤ x ≤ 0.2) have been prepared using a polymerlized complex method and sintering. The Seebeck coefficient, electrical conductivity, and thermal conductivity of the oxides were studied from room temperature to 773 K. The ln(σT)−1/T relationships revealed small-polaron hopping mechanism for the higher Sr contents. Large Seebeck coefficients were observed in lightly Sr-doped samples. Sr doping greatly reduced the Seebeck coefficient and enhanced the electrical and thermal conductivity of the samples. The temperature-induced spin-state transition of Co³⁺ ions strongly influenced the transport properties. The highest ZT value found in this series of oxides was 0.046 at 300 K for x = 0.1.     

Fluorine doping in dilute magnetic semiconductor Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

Recent studies have reported room-temperature ferromagnetism (FM) in Fe doped SnO₂. The FM in semiconductors due to transition metal doping has been argued to be carrier mediated. Fluorine (F) doping in pure SnO₂ has been reported to significantly increase the carrier concentration. In this work, we investigated the role of F doping in the range from 0% to 0.79% on the FM of chemically synthesized single phase Sn_1?x Fe _x O₂ using X-ray diffraction, UV–Vis spectrophotometry, particle-induced X-ray emission, particle-induced gamma ray emission and magnetometry. The saturation magnetization M _s (0.03 emu/g) increased by a factor of 2.5 and the lattice volume and band gap energy decreased by 0.35 Å³ and 0.2 eV, respectively, with 0.67% F doping (F/Sn atom %) compared to the sample without any fluorine.     

Facile synthesis and characterization of TiO<Subscript>2</Subscript>–graphene–ZnFe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Tb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4</Subscript> ternary nano-hybrids

Rare earth ion (Tb³⁺)-doped zinc ferrite (ZnFe₂O₄) nanoparticles grown on reduced graphene oxide (RGO) prepared through sol–gel method have been reported. During the sol–gel process, graphene oxide was reduced to RGO, and, subsequently, anatase TiO₂ and cubic spinel ZnFe_2?x Tb _x O₄ were grown in situ on the surfaces of the RGO nano-sheets. The structure, surface morphology and chemical composition of ternary nano-composites were studied using scanning electron microscopy, energy-dispersive X-ray, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, photoluminescence spectra and vibrating sample magnetometer (VSM). XRD results showed that the produced TiO₂ was composed of anatase and some rutile phases and ZnFe₂O₄ with a cubic spinel structure. The particle sizes of ZnFe₂O₄ and TiO₂ nanoparticles were in the ranges of ~65–80 and ~17–20 nm, respectively. The saturation magnetization (M _S) determined from VSM was found to linearly increase with Tb³⁺ concentration.     

Enhanced Superconductivity in Double-Doping Cu<Subscript>0.15</Subscript>TaSe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript><Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Superconducting Cu _x TaSe₂(x=0.05, 0.15) and Cu_0.15TaSe_2?x S _x (x=0, 0.5, 1, 1.5) single crystals have been systematically fabricated by a chemical vapor transport method. It is found that the double doping in TaSe₂, i.e., the simultaneous intercalation of Cu and substitution of Se by S, can substantially enhance the superconducting transition temperature. Transport property measurements give evidence of the coexistence and competition of charge density wave state and superconductivity in Cu _x TaSe₂ which provide meaningful information to understand the complex electronic states in this system. The parallel shift and the fan-shape broadening behaviors are observed in the superconducting transition curves under magnetic fields of Cu_0.15TaSeS and TaSeS, respectively, indicating an increase of coherence length and suppression of superconducting fluctuation induced by copper intercalation.     

Visible photoluminescence of hydrothermal synthesized Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> nanostructures

Sn_1−x Ni _x O₂ nanostructures such as nanocubes, nanospheres and hollow spheres were synthesized by a simple hydrothermal method. Room temperature photoluminescence spectra of the as-synthesized samples display a strong yellow emission at about 600 nm and a weak blue emission at about 430 nm. The as-prepared and annealed Sn_1−x Ni _x O₂ (x = 0, 0.01, 0.02, 0.04) were characterized by X-ray diffraction, field emission scanning electron microscopy, Raman spectrum, UV–Vis absorption spectra, and room temperature photoluminescence spectra. By investigating the relationship between the Raman band centered at 560 cm⁻¹ and the photoluminescence of the samples, we suggest that the broad yellow emission and weak blue emission primarily originate from singly ionized oxygen vacancies and tin interstitials, respectively.     

Anisotropic ferromagnetism in Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> nanostructure arrays

Periodic arrays of Fe _x Sn_1?x O₂ nanostructures were fabricated by glancing angle sputter deposition onto self-assembled close-packed arrays of 200-nm-diameter polystyrene microspheres. After annealing at 873 K for 3 h, all the films were crystallized to rutile SnO₂ and maintained good thermal stability in the morphology. Compared with Fe _x Sn_1?x O₂ flat films, arrays of Fe _x Sn_1?x O₂ nanostructures possessed larger saturation magnetic moment and exhibited both perpendicular and in-plane magnetic anisotropy, resulting from the anisotropic morphology of Fe _x Sn_1?x O₂ nanostructures. The EPR signal originating from the oxygen vacancies significantly varied with the Fe concentration and reached the strongest at x = 0.059, which is consistent with the saturation magnetization. It demonstrates that the oxygen vacancies are an important factor for the ferromagnetism of Fe _x Sn_1?x O₂ films.     

Synthesis and structural properties of AgCl<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Br<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0.5–0.8) solid solutions

The properties of AgCl_{1 - x} Br_x ( x = 0.5-0.8) solid solutions prepared by the Bridgman-Stockbarger method are studied using a variety of techniques (x-ray diffraction, microstructural examination, chemical analysis, and x-ray microanalysis). The lattice parameter of the solid solutions is found to exhibit a negative deviation from additivity. The effects of composition and preparation conditions on the structural properties of the solid solutions are discussed. The structural characteristics of abrasively polished surfaces of the samples are shown to be influenced by the preparation conditions.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 78–87. Original Russian Text Copyright © 2005 by Artjushenko, Baskov, Golovanov, Kuzmicheva, Lisitskii, Musina, Polyakova, Sakharov, Sakharova.     

Compositionally graded ceramics based on Ba<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> solid solutions

Homogeneous and compositionally graded barium strontium titanate (Ba_{1 − x} Sr _x TiO₃) ceramics have been prepared in the form of thick films by slip casting. The strontium content was varied across the graded films from 0 to 30 mol %. Microstructural examination and dielectric measurements have shown that, varying the composition and thickness of the layers in graded structures and the sintering conditions, one can control the behavior of their dielectric characteristics and obtain a small temperature coefficient of capacitance in a predetermined temperature range.     

Photocatalytic activities of LaFe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> nanocrystals prepared by sol–gel auto-combustion method

Nanophotocatalysts LaFe_1−x Zn _x O₃ (x = 0, 0.05, 0.1, 0.3, 0.5) were successfully prepared by sol–gel auto-combustion method. The samples were characterized by X-ray diffraction (XRD), ultraviolet/visible absorption spectra (UV–vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic activities of the prepared samples were investigated for the photodegradation of methylene blue (MB). The results show that the lattice constant of LaFe_1−x Zn _x O₃ nanocrystals increases due to the substitution of Zn for Fe, which leads to the lattice distortion. The absorption edges of Zn-doped LaFeO₃ display a red shift with a significant absorption between 400 and 500 nm. Doping with the Zn ions enhances the photodegradation rate of LaFeO₃ for MB. The LaFe_0.7Zn_0.3O₃ particles are spherical with mean grain size of about 20–30 nm, which exhibits the highest degradation rate of 75% under irradiation time of 150 min.     

Preparation and structural study of Mg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> ceramics and their dielectric properties from 1 Hz to 7.7 GHz

A series of Mg_1?x Zn _x TiO₃, x = 0–0.5 (MZT0–MZT0.5) ceramics was synthesised and characterised. The dielectric properties of the samples in the frequency range of 1 Hz–7.7 GHz were explored using three different methods: a contacting electrode method, a parallel-plate method and a perturbed resonator method. The electrical properties in the space charge and dipolar polarisation frequency ranges are discussed in relation to the phase composition and microstructure data. Differences in the zinc substitution divided the dielectrics into two groups, namely MZT0–MZT0.2 and MZT0.3–MZT0.5, each with different amount of a main Mg_1?x Zn _x TiO₃ solid solution phase and a secondary solid solution phase. Zinc substitution promoted the density of the ceramics, improved the purity of the main phase and increased the permittivity for frequencies up to 10⁸ Hz, but reduced the permittivity in the microwave range. In the MZT0.3–MZT0.5 samples, for frequencies less than 1 MHz the quality (Q × f) factors were lower and log σ _a.c, the AC conductivity, was higher than for the MZT0–MZT0.2 samples. Above 10 MHz, the (Q × f) factors and log σ _a.c of the two groups were similar.