Fabrication of hexagonal GaN on the surface of β-Ga2O3 single crystal by nitridation with NH3

The fabrication of GaN on the surface of a bulk β-Ga₂O₃ single crystal by nitridation with NH₃ was investigated for the purpose of using it as a substrate for GaN epitaxial growth. A β-Ga₂O₃ single crystal was prepared using a floating zone furnace with double ellipsoidal mirrors, and its polished (100) plane was nitridated in NH₃ atmosphere at 850 °C for 5 h. It was found that hexagonal GaN with preferred in-plane orientation was produced on the surface of β-Ga₂O₃, and the thickness of nitride layers was approximately 50 nm. High resolution transmission electron microscopic observation indicated that the synthesized GaN was composed of the aggregation with single crystalline GaN particles, whose size ranged from ∼ 5 nm to ∼ 50 nm, and dislocation or defect was not observed in a GaN particle. This method could be expected as a new route to fabricate a substrate for epitaxial growth of III-nitride materials instead of using a bulk GaN single crystal.     

Facile preparation and enhanced photocatalytic H2-production activity of Cu(OH)2 nanospheres modified porous g-C3N4

A facile precipitation approach for the preparation of Cu(OH)₂/g-C₃N₄ composite photocatalysts with good porous structure was developed for the first time. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible light (UV–vis) absorbance spectra, photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). A photocatalytic water splitting reaction on the as-prepared photocatalysts were carried out under visible light irradiation. The results revealed that the prepared samples showed significantly enhanced photocatalytic activity. The optimal Cu(OH)₂ loading content was found to be 0.34 mol%, giving an H₂-production rate of 48.7 μmol h⁻¹ g⁻¹, which is higher 16.5 times than that of pure g-C₃N₄. This high photocatalytic H₂-production activity is attributed to the presence of Cu(OH)₂ clusters on the surface of the porous g-C₃N₄, which efficiently promotes the visible light absorption and separation of photogenerated electron–hole pairs.     

One step room temperature photodeposition of Cu/TiO2 composite films and its conversion to CuO/TiO2

Cu/TiO₂ composite films were prepared at low temperature on glass substrates by a photodeposition method. Films were deposited by irradiating the substrate while in contact with an aqueous TiO₂ suspension containing copper(II) nitrate and ethanol. Cu/TiO₂ composite films of 500 nm in thickness were deposited at room temperature after a short irradiation time (15 min) with a 125 W mercury vapour lamp. According to scanning electron microscopy observations, the obtained films were homogeneous and porous. Energy dispersive X-ray spectroscopy analysis revealed a 3:1 Cu:Ti atomic ratio. Grazing angle X-ray diffraction analysis showed that the films contained Cu and TiO₂ as major components and Cu₂O as a minor component. Heat treatment at 400 °C in air for a period of 3 h transformed the initial material into a CuO/TiO₂ composite, improved the adhesion to the substrate and favoured a more regular distribution of copper oxide according to backscattering micrographs.     

Structural and thermochemical properties, and energetics of C8(NO2)8 and C20(NO2)4n (n = 0–4)

Density-functional-theory calculations, at the B3LYP level with the 6–31 G basis set, have been performed to investigate the structural and electronic properties of octanitrocubane, C₈(NO₂)₈, and polynitrofullerenes of type C₂₀(NO₂)_4n, with n = 0–4, in their ground states. Having determined their energetically optimized geometric structures, energetics, and vibrational frequencies, we have calculated the enthalpies of combustion and decomposition of these molecules. Extrapolating from the so-obtained data, we have also estimated, as a by-product, the enthalpy values of C₂₀(NO₂)₂₀.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

Zur kristallstruktur von (NH4)3Ti(O2)F5

The disordered ligand positions in (NH₄)₃Ti(O₂)F₅ (cubic, space group Fm3m - O⁵_h'$\text{a}\text{= 9.23}{}_2\text{A}\text{?}$) has been studied by X-ray single crystal investigation. A 3-dimensional fourier synthesis indicates a distribution of the disordered O-Atoms on the 96j positions (Oyz) similar to (NH₄)₃ZrF₇ where a pentagonal bipyramide has been proposed for geometrie of the ZrF₇-group. Due to the short O-O distance the structure of (NH₄)₃Ti(O₂)F₅ is better described as elpasolite where one of the six octahedral ligand positions are statistically replaced by an ‘edge on’ O^2?₂-group oriented there in two possible directions.     

Optical and hydrophilic properties of nanostructure Cu loaded brookite TiO2 thin film

Copper loaded TiO₂ brookite thin films were deposited on glass substrates using the dip-coating method. The crystalline structure of the films was characterized by X-ray diffraction analysis. X-ray photoelectron spectroscopy was used to evaluate the properties of the film surfaces. The transmittance spectra of the films were obtained by the Shimadzu multi-purpose spectrophotometer. The water contact angle on the film surfaces during irradiation and storage in a dark place was measured by a contact angle analyzer. The results indicate that Cu loading did not affect the transmittance spectra, whereas it had a significant effect on the hydrophilicity of the TiO₂ film surface.     

Description of TiO2 thin films treated in NH3 atmosphere by optical dispersion models

The influence of a reductive ammonia atmosphere on TiO₂ sol-gel film structural and optical characteristics was investigated. X-ray Diffraction technique, X-ray photoelectron spectroscopy and Rutherford Back Scattering analysis were applied to study the crystallinity, oxidation state and element concentration profile of the modified films. Their optical properties were investigated by UV-Vis spectroscopy. The refractive index and extinction coefficient were obtained by fitting theoretical transmittance curves to experimental ones using Forouhi-Bloomer (FB) and Tauc-Lorentz (TL) physical models. Both models revealed slight decrease (up to 2.6-2.7 eV) of the FB and TL band gaps with increase of the treatment temperature. These results were discussed in terms of the additional energy levels creation due to the defect TiO₂ structure formation during thermal treatment in reductive atmosphere.     

Hydrothermal Crystallization in the Systems La2(CO3)3 ? 6H2O-CaCO3(BaCO3)-R-H2O (R = Na2CO3, K2CO3, NaHCO3, KHCO3, NaCl, NH4Cl, CO(NH2)2)

Crystallization in the systems La₂(CO₃)₃ ⋅ 6H₂O-CaCO₃(BaCO₃)-R-H₂O (R = Na₂CO₃, K₂CO₃, NaHCO₃, KHCO₃, NaCl, NH₄Cl, CO(NH₂)₂) was studied under hydrothermal conditions (400–450°C). The solid reaction products were found to contain LaOHCO₃ and NaLa(CO₃)₂. Detailed thermal decomposition schemes were proposed for these phases, and their lattice parameters were refined. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 11, 2005, pp. 1366–1372. Original Russian Text Copyright ? 2005 by Nikol'skaya, Dem'yanets.     

Interface phenomena in the Y2O3/(Al–Cu) system

Wetting behavior and the interface reaction in the Y₂O₃/(Cu–Al) system were investigated at 1423 K. A contact angle of about 130° was measured in the Y₂O₃/Cu system. Aluminum addition to copper improves wetting and the transition from non-wetting to wetting (θ ≤ 90°) was observed for the alloy with 50 at.% Al. The microstructure examination of the interface indicates that Al reacts with yttria, yttrium dissolves in the melt and a crater of AlYO₃ is formed at the substrate. The interface interaction in the Y₂O₃/(Cu–Al) system is in a good agreement with the results of a thermodynamic analysis in the Y–Al–Cu–O system. The crater depth and the macroscopic final contact angles are correlated with the Y and Al activities in the melt.     

Fine Fe16N2 powder prepared by low-temperature nitridation

α-Fe was prepared by reduction of a fine γ-Fe₂O₃ powder under hydrogen at 500 °C for 8 h. The α-Fe fine powder, about 100 nm in crystallite size, was then nitrided under an ammonia flow at 130 °C for 100 h. X-ray single-phase Fe₁₆N₂ was obtained with a magnetization value of 225 emu/g at room temperature under a magnetic field of 15 kOe. The Mössbauer spectrum at room temperature could be resolved into three sets of hyperfine fields with an average magnetic moment of 2.52 μ_B. An additional paramagnetic component was present in the spectrum with an area ratio of 19%.     

Preparation of the rod-like β-Si3N4 particles favoring the self-reinforcing Si3N4 ceramics

The β-Si₃N₄ particles were prepared by heating original α-Si₃N₄ powder with rare earth oxide Nd₂O₃ or Yb₂O₃ additives at 1600-1700 °C for 1.5 h. The transformation ratio of α-Si₃N₄ was also investigated by XRD. The results showed that Yb₂O₃ could accelerate the transformation of Si₃N₄ more effectively than Nd₂O₃ and the powder heated at 1700 °C with over 4 wt.% Yb₂O₃ has a high transformation ratio of over 98%. The morphologies of the heated powders were observed by scanning electron microscopy. The results showed that the powder heated at 1700 °C with 4 wt.% Yb₂O₃ had ideal β-Si₃N₄ rod-like morphology particles. This heated powder was used as a seed by adding it to the original α-Si₃N₄ powder to prepare self-reinforced Si₃N₄ ceramic by hot-pressed sintering. The fracture toughness of the seeded Si₃N₄ ceramics increased to 9.1 MPa m^1/2 from 7.6 MPa m^1/2 of the unseeded Si₃N₄ ceramics, while the high value of strength was still kept at 1200 °C.     

Porous titanium (Ti) scaffolds by freezing TiH2/camphene slurries

Porous titanium (Ti) scaffolds with interconnected pores were fabricated by freezing titanium hydride (TiH₂)/camphene slurries at 33 °C for 24 h, followed by freeze-drying and subsequent heat-treatment at 1300 °C for 2 h in vacuum. All of the fabricated samples revealed highly porous structures having large pores up to 100 μm in size surrounded by Ti metal walls without any secondary phases. When the initial TiH₂ content was increased from 15 to 25 vol.%, the porosity was decreased from 63 to 49%, while the compressive strength was significantly improved from 81 to 253 MPa.     

真空钙热还原法制备金属钛粉的研究

在真空炉中(30~40 Pa)1273 K下,将物料放入螺纹密封的石墨坩埚中进行不同时间下的还原反应。本文采用热力学分析及X射线衍射、扫描电子显微镜及能量弥散X射线谱等方法与手段,系统研究了金属钙(Ca)与反应器中的氧气(O2)、氮气(N2)、二氧化钛(TiO2)的反应和还原时间及还原产物的预处理对得到金属钛粉(Ti)的影响。通过热力学研究,在温度低于钙的熔点(1115 K)时,密封容器内的O2与Ca的反应及N2与Ca的反应满足反应发生的热力学条件。当温度达到1273K时,Ca的饱和蒸气压p*≈p系,有利于整个气固反应进行。实验研究表明,在还原反应发生前,反应器内的O2,N2与Ca反应完全。将在1273 K下还原时间为4 h得到的还原产物在酸洗前真空挥发处理还原产物表面大量的Ca时,金属单质Ti再次被氧化成低价氧化物,最终得不到金属Ti粉。将反应时间延长至6 h时,酸洗过滤后得到形状不规则、纯度达到98.64%的Ti粉。     

(Fe,Ti) 16N2 films with high saturation magnetization prepared by facing target sputtering

(Fe,Ti)-N films with a Ti concentration of 10 at.% were prepared on Si(100) and NaCl substrates by facing targets sputtering. The effects of the nitrogen pressure (P_N) and the substrate temperature (T_s) on the formation of various (Fe,Ti)-N phases and their microstructures were investigated in detail. X-ray diffractometer and transmission electron microscope provided complete identification of the phases present in the films and the characterization of their microstructures. Films deposited at a lower P_N = 1 3 × 10⁻² Pa or a lower T_s = RT consist of mainly -phase. Films deposited at a higher P_N = 1.3 2 × 10⁻¹ Pa or a higher T_s = 200 °C contain a great many γ' and Fe₂N phases with a higher nitrogen content. When P_N = 4 7 × 10⁻² Pa and T_s = 100 150 °C, it is advantageous to the formation of ′' phase. These films exhibit a high saturation magnetization (M_s) up to the range of 2.3 2.5 T, which is larger than that of pure iron.     

Reaction sintering fabrication of (AlN, TiN)-Al2O3 composite

The (AlN, TiN)-Al₂O₃ composites were fabricated by reaction sintering powder mixtures containing 10-30 wt.% (Al, Ti)-Al₂O₃ at 1420-1520°C in nitrogen. It was found that the densification and mechanical properties of the sintered composites depended strongly on the Al, Ti contents of the starting powder and hot pressing parameters. Reaction sintering 20 wt.% (Al, Ti)-Al₂O₃ powder in nitrogen in 1520°C for 30 min yields (AlN, TiN)-Al₂O₃ composites with the best mechanical properties, with a hardness HRA of 94.1, bending strength of 687 MPa, and fracture toughness of 6.5 MPa m^1/2. Microstructure analysis indicated that TiN is present as well dispersed particulates within a matrix of Al₂O₃. The AlN identified by XRD was not directly observed, but probably resides at the Al₂O₃ grain boundary. The fracture mode of these composites was observed to be transgranular.     

CuS nanotubes prepared using Cu(OH)2 nanowires as self-sacrificial template

Copper sulfide (CuS) nanotubes assembled with nanoparticles have been successfully synthesized by microwave-assisted solvothermal method at 80 °C using Cu(OH)₂ nanowires in the solvent of ethylene glycol. Cu(OH)₂ nanowires act as both the precursor and template for the preparation of CuS nanotubes assembled with nanoparticles. Cu(OH)₂ nanowires are prepared by adding an aqueous solution containing CuCl₂ into an alkaline solution at room temperature and by ultrasonication for 30 min. This method has the advantages of the simplicity and low cost. The samples are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The method reported herein may be extended to the synthesis of nanotubes of other copper-containing compounds.     

Realization of superhard nanocomposites with sufficient toughness: Superlattice nanocrystal-TiN/amorphous-(W,Ti)C0.83 films

A superhard nanocrystal (nc)-TiN/amorphous (a)-(W,Ti)C_0.83 film with sufficient toughness was synthesized by arc ion plating and dc magnetron sputtering. The superlattice structure of nc-TiN/a-(W,Ti)C_0.83 with a modulation period of 10 nm was obtained on amorphous (Ti,W)C_1 − x bonding layers. Accordingly, the nc-TiN/a-(W,Ti)C_0.83 nanocomposite showed a superhard effect (~ 52 GPa), meanwhile, exhibiting a sufficient toughness (~ 590 MPa). Compared to TiN films, the friction and wear performance of nc-TiN/a-(W,Ti)C_0.83 was significantly improved. As such, the superlattice nc-TiN/a-(W,Ti)C_0.83 nanocomposites have good potential in high-speed drying machines and high-temperature applications.     

Etude du systeme KPO3-LaP3O9. Donnees cristal lographiques sur K2La(PO3)5 et (NH4)2La(PO3)5

The system KPO₃-LaP₃O₉ has been studied for the first time by differential thermal analysis and X ray diffraction. The system shows two compounds KLa(PO₃)₄ and K₂La(PO₃)₅ which melt in a peritectic decomposition at 880°C and 770°C respectively. An eutectic point appears at 705°C; The eutectic point corresponds to a concentration of 10% molar LaP₃O₉.Infra Red absorption spectra are typical of chain phosphates.The new compound K₂La(PO₃₅ is isotypic whith (NH₄)₂La(PO₃)₅ which has been synthetized for the first time. They belong to the triclinic system whith space group P1 and Z = 2. The parameters of the unit cell are: $\text{a = 7.309(4)}\text{A}\text{?}$$\text{b = 13.35(2)}\text{A}\text{?}$$\text{c = 7.155(7)}\text{A}\text{?}$α = 90°3(1) β = 109°17(7) γ = 89°90(4) for K₂La(PO₃)₅ and: $\text{a = 7.174(8)}\text{A}\text{?}$$\text{b = 13.38(2)}\text{A}\text{?}$$\text{c = 7.35(2)}\text{A}\text{?}$α = 90°6(2) β = 107°4(1) γ = 89°82(7) for (NH₄)₂La(PO₃)₅.     

Role of Ti out-diffusion from a Pt/Ti bi-layer on the crystalline growth of (Ba,Sr)TiO3: A transmission electron microscopy investigation

We investigated the influence of the Ti out-diffusion in Pt/TiO_x/SiO₂/Si substrates (0 ≤ x ≤ 2), having different thicknesses of Pt and TiO_x layers, on the crystalline growth of (Ba,Sr)TiO₃ (BST) deposited by pulsed laser deposition. By means of X-ray diffraction and transmission electron microscopy, we show that the orientation of BST clearly depends on the presence and quantity of Ti having migrated up to the Pt surface, and on its possible oxidation prior to BST deposition, which was controlled by the atmosphere (vacuum or oxygen) of the pre-heating stage of the BST deposition process. Whereas BST has no preferential orientation if grown on a bare Pt surface, a strong (111) orientation of BST is obtained for a limited diffusion of titanium oxides on the Pt surface just before BST deposition. However, the (111) orientation is lost if this seeding titanium oxide layer on Pt is too thick just before BST deposition. Also, the formation of protrusions was evidenced at the BST/Pt interface and associated with the oxidation of Ti within the Pt layer.