Synthesis and properties of β-Ga2O3 nanostructures

A novel method was utilized to synthesize one-dimensional β-Ga₂O₃ nanostructures. In this method, β-Ga₂O₃ nanostructures have been successfully synthesized on Si(111) substrates through annealing sputtered Ga₂O₃/Mo films under flowing ammonia in a quartz tube. The as-obtained samples were analyzed in detail using the methods of X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDX) attached to the HRTEM instrument. The results show that the formed nanostructures are single-crystalline Ga₂O₃. The annealing temperature has an evident influence on the morphology of the β-Ga₂O₃ nanostructures. The growth mechanism of the β-Ga₂O₃ nanostructures is also discussed by conventional vapor-solid (VS) mechanism.     

Synthesis and characterization of crystalline β-Bi2O3 nanobelts

We synthesized β-Bi₂O₃ nanobelts on silicon substrates without using a metal catalyst. Trimethylbismuth and O₂ were taken as the source of bismuth and oxygen, respectively. X-ray diffraction and transmission electron microscopy studies confirmed the formation of tetragonal Bi₂O₃ phase. The typical width of the β-Bi₂O₃ nanobelts was in the range of 40-400 nm. We suggested that the growth of β-Bi₂O₃ nanobelts was mainly controlled by a vapor-solid mechanism. Photoluminescence measurements at room temperature exhibited a visible light emission band peaking at around 2.81 eV.     

Phase-transitions of α- and β-Bi2O3 nanowires

The transition temperatures for the α or β to δ and the δ to liquid phase for α- and β-Bi₂O₃ nanowires were investigated. We found that there is a size effect for the δ to liquid phase transition but not the α or β to δ phase transition. This is because the δ to liquid phase transition involves bond rupture as well as surface area reduction, whereas the α or β to δ is only solid-solid phase transition, which requires only the reorganization of the bonds. This is the first time the phase transitions of the Bi₂O₃ nanowires have been investigated and their size effect revealed.     

Optical and structural properties of Cu-doped β-Ga2O3 films

The intrinsic and Cu-doped β-Ga₂O₃ films were grown on Si and quartz substrates by RF magnetron sputtering in an argon and oxygen mixture ambient. The effects of the Cu doping and the post thermal annealing on the optical and structural properties of the β-Ga₂O₃ films were studied. The surface morphology, microstructure, optical transmittance, optical absorption, optical energy gap and photoluminescence of the β-Ga₂O₃ films were significantly changed after Cu-doping. After post thermal annealing, Polycrystalline β-Ga₂O₃ films were obtained, the transmittance decreased. After Cu-doping, the grain size decreased, the crystal quality deteriorated and the optical band gap shrunk. The UV, blue and green emission bands were observed and discussed. The UV and blue emission were enhanced and a new blue emission peak centred at 475 nm appeared by Cu-doping.     

Microwave-assisted preparation of Ca6Si6O17(OH)2 and β-CaSiO3 nanobelts

Xonotlite (Ca₆Si₆O₁₇(OH)₂) nanobelts were synthesized by a microwave-assisted hydrothermal method at 180 °C for 90 min independent of the feeding molar ratio of Ca(NO₃)₂·4H₂O to Na₂SiO₃·9H₂O in the range of 0.8-3.0. Crystalline wollastonite (β-CaSiO₃) nanobelts were obtained by microwave thermal transformation of Ca₆Si₆O₁₇(OH)₂ nanobelts at 800 °C for 2 h. Ca₆Si₆O₁₇(OH)₂ nanobelts were used as both the precursor and the template for the preparation of β-CaSiO₃ nanobelts. The morphology and size of Ca₆Si₆O₁₇(OH)₂ nanobelts could be well preserved during the microwave thermal transformation process. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED).     

PP/PA6/nano-CaCO3三元复合材料的结晶行为

通过应用偏光显微镜、广角X射线衍射、差示扫描量热(DSC)等手段分析和表征了PP/PA6/nano-CaCO3聚丙烯三元复合材料共混体系各组分对其结晶性能的影响。研究发现,PA6、nano-CaCO3对改性聚丙烯复合材料均有诱导成核结晶的作用,加入nano-CaCO3的复合材料的诱导结晶作用要高于加入PA6的复合材料,同时复合材料的结晶温度和结晶速率得到提高。改性后的复合材料结晶度都有不同程度的下降,其中PP/PA6/POE-g-MAH的结晶度为31.83%,PP/PA6/nano-CaCO3/POE-g-MAH的为33.83%。     

Synthesis of ZnGa2O4 nanowires with β-Ga2O3 templates and its photoluminescence performance

This paper focuses on a new but much simple approach in synthesizing cubic spinel-structure ZnGa₂O₄ nanowires through the reaction of β-Ga₂O₃ nanowires templates and ZnO vapor at high temperature. Characterization has been achieved by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The length of as-synthesized ZnGa₂O₄ nanowires is scaled over 10 μm and the diameter is 80 nm respectively. It has been noticed that the concentration of ZnO vapor plays an important role for synthesizing ZnGa₂O₄ nanowires. And with different concentration of ZnO vapor, the very nanowires could be compounded in the form of β-Ga₂O₃:ZnGa₂O₄, ZnGa₂O₄ and ZnO:ZnGa₂O₄. The corresponding photoluminescence emission bands centered at 460 nm, 405 nm and 381 nm have also been observed.     

Charge and Sodium Ordering in β-Na0.33V2O3

Polarized Raman and optical spectra for the quasi one-dimensional metallic vanadate -Na_0.33V₂O₃ are reported for various temperatures. The spectra are discussed in the light of the sodium and charge ordering transitions occurring in this material, and demonstrate the presence of strong electron–phonon coupling.     

Fabrication and structure characterization of MnCO3/α-Fe2O3 nanocrystal heterostructures

Novel MnCO₃/α-Fe₂O₃ nanocrystal heterostructures, with MnCO₃ nanorods 5-10 nm in diameter and 15-50 nm in length, grown onto the surfaces of the α-Fe₂O₃ nanohexahedrons sized around 30-50 nm, were fabricated via a two-step solvothermal route. The coalescent planes of the heterostructure for the MnCO₃ nanorod and the α-Fe₂O₃ nanohexahedron were determined to be (01?4) and (110), respectively. The formation of the MnCO₃ nanorods from the Mn contained amorphous flakes was tracked by transmission electron microscopy observations at various reaction stages, which suggested a rolling-broken-growth process. Evidenced by the comparative experimental result, the α-Fe₂O₃ nanohexahedrons played an important role in inducing the nucleation and growth of the hexagonal MnCO₃ nanorods on their surfaces.     

Ferroelectric and ferromagnetic properties of Gd-doped BiFeO3–BaTiO3 solid solution

The solid solutions of Bi_1−x−yGd_xBa_yFe_1−yTi_yO₃ have been prepared via solid-state reaction method with the aim to obtain magnetoelectric coupling (i.e., linear relation between magnetization and electric field) at room temperature. Optimum calcination and sintering strategies for obtaining pure perovskite phase, high density ceramics and homogeneous microstructures have been determined. All the samples of the composition Bi_1−x−yGd_xBa_yFe_1−yTi_yO₃ (x = 0.1 and y = 0.1, 0.2, and 0.3) reported in the present work are tetragonal at room temperature. The maximum ferroelectric transition temperature (T_c) of this system was 150–170 °C with the dielectric constant peak of 2300 at 100 kHz for y = 0.1. Above T_c the dielectric constant is decreasing up to a certain temperature and then increasing with temperature similar to that observed in other perovskites due to chemical inhomogeneities in both A and B sites of the ABO₃ cell. The variation of ferroelectric and magnetic properties was followed by piezoresponse force microscopy and vibrating sample magnetometer, respectively. Well-saturated piezoelectric loops were observed for all composition indicating room temperature ferroelectricity.     

Dielectric and piezoelectric properties of BiMnO3 doped 0.95Na0.5K0.5NbO3–0.05LiSbO3 ceramics

The piezoelectric properties of (1 − x)(0.95K_0.5Na_0.5NbO₃–0.05LiSbO₃)–x BiMnO₃ (x = 0, 0.002, 0.004, 0.006, 0.008, 0.01) lead-free piezoelectric ceramics were investigated as a function of x. These ceramics were fabricated by conventional ceramics sintering processing. BiMnO₃ (BM)-doping was found to increase the Curie temperature, T _c, from 370 °C at x = 0–380 °C at x = 0.002, and clearly increase the d ₃₃, Q _m and k _p values, showing “hard” characteristic. The good piezoelectric and electromechanical properties of d ₃₃ = 226pC/N, k _p = 40.8%, tan θ = 2.60% and T _c = 370 °C appear at x = 0.004.     

Effects of copper and Al2O3 particles on characteristics of Cu–Al2O3 composites

High-energy milling was used for production of Cu–Al₂O₃ composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al₂O₃ powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al₂O₃ particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al₂O₃ particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al₂O₃ particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al₂O₃ composites.     

Dielectric Relaxation and Conductivity of Ba(Mg1/3Ta2/3)O3and Ba(Zn1/3Ta2/3)O3

The frequency dependent dielectric properties of barium magnesium tantalate(BMT),Ba(Mg_(1/3)Ta(2/3))O_3 and barium zinc tantalate(BZT),Ba(Zn_(1/3)Ta_(2/3))O_3 synthesized by solid state reaction technique have been investigated at various temperatures by impedance spectroscopy.BMT and BZT possess cubic structure with lattice parameter a = 0.708 and 0.451 nm,respectively.The resonance peaks due to dielectric relaxation processes are observed in the loss tangent of these oxides.The relaxation in the samples is polydispersive in nature.The temperature dependence of dc conductivity,the most probable relaxation frequency(ω_m) obtained from tanδ vs logw plots and ω_m obtained from imaginary parts of the complex electrical modulus vs logw plots follow the Arrhenius behavior.According to these Arrhenius plots the activation energies of BMT and BZT are about 0.54 and 0.40 eV,respectively.Thus the results indicate that samples are semiconducting in nature.The frequency-dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms.Both these formalisms show qualitative similarities in relaxation time.Our study points that for complex perovskite oxides with general formula A(B'B")O_3,the dielectric properties significantly depend on the atomic radii of both A and B type cations.BMT and BZT exhibit enhancement in dielectric property compared to their niobate counterparts.They may find several technological applications such as in capacitors,resonators and filters owing to their high dielectric constant and low loss tangent.     

Structure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCoO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ (x = 0.12–0.24, y = 0–0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y ≤ 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral–tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d ₃₃ = 156 pC/N and electromechanical coupling factor k _p = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO₃ leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric–antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ ceramics are good candidate for use as lead-free ceramics.     

Synthesis and properties of magnetic solid superacid: SO4/ZrO2–B2O3–Fe3O4

A magnetic SO₄²⁻/ZrO₂–B₂O₃–Fe₃O₄ solid superacid catalyst is prepared via a simple chemical co-precipitation approach. The obtained materials were characterized in detailed by X-ray powder diffraction, thermogravimetric analysis–different scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM and TEM), and Mossbauer spectra. Powder X-ray diffraction patterns show that in this composite oxide the transformation temperature of ZrO₂ from tetragonal to monoclinic phase is higher compared to the pristine SO₄²⁻/ZrO₂ material. The introduction of Fe₃O₄ endows the superacid with a super-paramagnetic property while in a ferromagnetic state after calcination. The superacid exhibits high catalytic activity in forming ethyl acetate by esterification.     

β-Cyclodextrin-assisted preparation of hierarchical walnut-like CeOHCO3 and CeO2 mesocrystals

The hierarchical walnut-like CeOHCO₃ mesocrystals were prepared by a facile hydrothermal method under low temperature with β-cyclodextrin (β-CD) as assistant agent. The hierarchical walnut-like CeO₂ mesocrystals were obtained by thermal decomposition of CeOHCO₃ mesocrystals. The crystal phase, morphology, and structure of CeOHCO₃ and CeO₂ mesocrystals were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The time-dependent experimental results indicated that the morphology transformation from shuttle-like to walnut-like and the crystal phase transformation from orthorhombic to hexagonal simultaneously occurred in the formation processes of CeOHCO₃ mesocrystals. On the basis of the morphological and crystal phase evolution processes, the formation mechanism of hierarchical walnut-like CeOHCO₃ mesocrystals, including dissolution-recrystallization processes, was discussed. β-CD was believed to play an important role in the formation of the hierarchical walnut-like CeOHCO₃ mesocrystals. The effects of reaction temperature, β-CD amount, and concentration of reactants on the morphologies of the products were systematically studied. CeO₂ mesocrystals exhibited the distinct red-shift phenomenon in UV-vis absorption spectra.     

Optical properties and structure of R2O–Ga2O3–SiO2 and RO–Ga2O3–SiO2 glasses

Refractive index and molar refraction of Li₂O–, Na₂O–, CaO–, and BaO–Ga₂O₃–SiO₂ glasses have been used to test the validity of a structural model of silicate glasses containing Ga₂O₃ glasses. Ga₂O₃ enters these types of glass in a similar manner as Al₂O₃. It is assumed that, for (SiO₂/Ga₂O₃) >1 and (Ga₂O₃/R₂O) ≤1, Ga₂O₃ associates primarily with modifier oxides to form GaO₄ units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values suggest another structure for (Ga₂O₃/SiO₂) ≥1.     

Synthesis and photoluminescence properties of Eu-doped γ-Ca3(PO4)2

Eu³⁺-doped (1% and 3%) γ-Ca₃(PO₄)₂ was synthesized by high-pressure and high-temperature experimental method and the samples were characterized by X-ray diffraction. The luminescence properties of samples were investigated by emission and excitation spectra. The excitation spectra of Eu³⁺-doped γ-Ca₃(PO₄)₂ showed that samples were mainly attributed to Eu³⁺–O²⁻ charge-transfer band at 270 nm, and some sharp lines were also attributed to Eu³⁺ f–f transitions in near-UV regions with the strongest peaks at 395 nm. Under the 395 nm excitation, the intense red emission peak at 611 nm was observed. The strongest line (395 nm) in excitation spectra of those phosphors matched well with the output wavelength of UV InGaN-based light-emitting diodes (LEDs) chip. The luminescent properties suggested that Eu³⁺-doped γ-Ca₃(PO₄)₂ might be regarded as a potential red phosphor candidate for near-UV LEDs.     

Structure study of MoO3-ZnO-B2O3 glasses by Raman spectroscopy and formation of α-ZnMoO4 nanocrystals

Molybdenum oxide (MoO₃)-containing glasses of xMoO₃-50ZnO-(50−x)B₂O₃ (x = 10, 20, and 30) are prepared using a conventional melt quenching method, and the glass structure and crystallization behaviour are clarified. It is found that the thermal stability against crystallization of the glasses decreases drastically with increasing MoO₃ content. The main valence of Mo ions in the glasses is found to be Mo⁶⁺ from X-ray photoelectron spectroscopy measurements. The Raman bands observed at ∼860 cm⁻¹ and 950 cm⁻¹ suggest that the coordination state of Mo⁶⁺ ions in the glasses is mainly (MoO₄)²⁻ tetrahedral units. All glasses examined in this study give the formation of α-ZnMoO₄ as the initial crystalline phase. In particular, 30MoO₃-50ZnO-20B₂O₃ glass shows the bulk crystallization of α-ZnMoO₄ nanocrystals with a diameter of ∼5 nm. The crystallized glasses consisting of Eu³⁺-doped ZnMoO₄ crystals are synthesized, and enhanced photoluminescence emissions (i.e., the quantum yield is 9%) due to the 4f transitions ⁵D₀ → ⁷F_J (J = 0-4) of Eu³⁺ ions is observed.     

Synthesis and electrochemical performance of β-MnO2 with semi-tubular morphology

β-MnO₂ with semi-tubular morphology has been prepared in a mixed solution of KMnO₄ and MnCl₂ by a facile hydrothermal route without using templates, catalysts, and organic reagents. The structure of the obtained β-MnO₂ is systematically investigated by XRD, SEM, and TEM. Results show that the as-prepared β-MnO₂ has novel semi-tubular morphology, and its particle shows a diameter of 300–400 nm and length up to 1–4 μm. The prepared β-MnO₂ shows a good electrochemical performance, and delivers a discharge capacity of 195 mAh g⁻¹ after 40 cycles between voltage limit of 1.5 and 4.5 V at a constant current density of 20 mA g⁻¹.