Density studies of liquid alloys SnAg and SnZn with near eutectic compositions

The density values for SnAg and SnZn alloys with near eutectic compositions were determined by the gamma-absorption method both in the liquid and solid states. Sn-rich melts of the AgSn system were found to be microheterogeneous, whereas SnZn melts demonstrate the behavior typical for true solutions.     

First principles study of oxygen-deficient centers in pure and Ge-doped silica

Using ab initio calculations on 108 atoms pure- and Ge-doped (2.8 mol%) silica-based supercells, we performed a statistical study on the electronic structure and energetic contribution of neutral oxygen vacancies, also named Oxygen Deficient Centers (ODCs). All the 72 oxygen sites in the amorphous silica (a-SiO₂) cell were considered as possible candidates for the formation of the vacancies leading to study 72 different Si-ODCs (SiSi bond) and 144 Ge-ODCs (GeSi bond). The distributions of structural parameters and formation energies of the ODCs were evaluated through Density Functional Theory calculations. The obtained parameters showed a wide distribution that can be mainly associated with the differences in the local environments surrounding the point defects. We show that the formation energies of Si and Ge-ODCs generated from the same oxygen site of our supercell are correlated. Moreover, the local asymmetry around the SiGe or GeSi bond can also affect their formation energies, providing a strong evidence for the influence of short-range environment on the ODC generation efficiency.     

Eu:Lu2O3透明闪烁陶瓷的制备与性能

采用湿化学法合成了Eu原子掺量5%的Lu₂O₃陶瓷前驱体,通过SEM、XRD研究了煅烧前后前驱体和1 100 ℃煅烧4 h后粉体的形貌、结构以及物相。结果表明煅烧后的粉体为纳米类球形、高分散且结晶性良好的颗粒。颗粒尺寸为68.5 nm。使用煅烧后的粉体为原料,在1 650 ℃真空烧结30 h制备了高透过率的Eu:Lu₂O₃陶瓷,晶粒尺寸为46 μm,在611 nm处的直线透过率可以达到66.3%。此外对陶瓷的吸收曲线、光致激发和发射光谱特性以及X射线激发发射光谱进行研究。可观察到,Eu:Lu₂O₃陶瓷存在基质和激活离子两类吸收,光致发光光谱和X射线激发发射光谱均可以看出Eu:Lu₂O₃陶瓷存在极强的⁵D₀→⁷F₂跃迁发光,位于611 nm处。对比商业的BGO单晶的X射线发射光谱,可得本实验中制备的陶瓷的光输出为85 000 ph/MeV。Eu:Lu₂O₃陶瓷本身有着高X射线以及高能粒子的阻止能力,结合高光输出特性,表明Eu:Lu₂O₃陶瓷在X射线成像等领域具有巨大的潜在应用价值。     

Dependence of the Electric Properties and the Positron Lifetimes on the Dopant Content in La-doped SrTiO3

The resistivity, the dielectric constant, and the positron lifetimes in La-doped SrTiO₃ have been measured for La content x of 0—10 at.%. It was found that with increasing x, the variations of the resistivity and the dielectric constant and the positron lifetime parameters are nonmonotonic. The positron experiments have shown that the La-doping induces mainly formation of Sr vacancies and variation of Sr vacancy configuration; the most probable configuration is the isolated Sr vacancies (V) as x < 0.5 at.%, the associated defects (La V) for 0.5 < x < 1 at.%, and the associated defects (2 La V) above x = 1 at.%. The results suggest that the variation of the resistivity can be regarded as variation of electron density, and the variation of the dielectric constant results mainly from variations of the space-charge polarizaion and Sr-vacancy concentration and configuration.     

Interplay of ballistic and chemical effects in the formation of structural defects for Sn and Pb implanted silica

The electronic structures of Sn and Pb implanted SiO₂ are studied using soft X-ray absorption (XAS) and emission (XES) spectroscopy. We show, using reference compounds and ab initio calculations, that the presence of PbO and SnO interactions can be detected in the pre-edge region of the oxygen K-edge XAS. Via analysis of this interaction-sensitive pre-edge region, we find that Pb implantation results primarily in the clustering of Pb atoms. Conversely, with Sn implantation using identical conditions, strong SnO interactions are present, showing that Sn is coordinated with oxygen. The varying results between the two ion types are explained using both ballistic considerations and density functional theory calculations. We find that the substitution of Pb into Si sites in SiO₂ requires much more energy than substituting Sn in these same sites, primarily due to the larger size of the Pb ions. From these calculated formation energies it is evident that Pb requires far higher temperatures than Sn to be soluble in SiO₂. These results help explain the complex processes which take place upon implantation and determine the final products.     

Erratum to:Influence of Chlorides of Mono- and Divalent Metals on the Oligomeric Composition of Lysozyme Crystallization Solutions and Further Crystal Growth

Crystallography Reports - An Erratum to this paper has been published: https://doi.org/10.1134/S1063774521340046     

Growth and properties of (Cr, Nd) doped GdCa4O(BO3)3 crystals

Optical quality Nd:GdCa₄O(BO₃)₃ (Nd:GdCOB) crystal and chromium sensitized crystal of Cr:Nd:GdCa₄O(BO₃)₃ (Cr:Nd:GdCOB) were grown by the Czochralski (CZ) method. The transmittance spectra was measured at room temperature on 7at%Nd:GdCOB and lat%Cr:7at%Nd:GdCOB samples. The absorption in the blue-UV region of Cr:Nd:GdCOB was larger than that of Nd:GdCOB, which matched the xenon flash lamp very well. A 3×3×10mm³ Nd:GdCOB sample without any antireflective coating was sidepumped using a pulsed dye-laser tuned to 595.4nm. The green-light output energy was 1.35mJ at a pump energy of 17.5mJ. The conversion efficiency was 7.7%, and the threshold energy was less than 1.2mJ which are the best results up to now to our knowledge. 3×3×7mm³ Nd:GdCOB and Cr:Nd:GdCOB samples without antireflective coatings were pumped using a flash pump source. The threshold for Cr:Nd:GdCOB was 0.9J while for Nd:GdCOB it was I.O.J. The output green light energy was 2.46mJ for Cr:Nd:GdCOB at a 10J flash pump energy and was 1.96mJ for Nd:GdCOB at the same pump energy, which clearly shows that Cr³⁺ ions have the sensitizing effect on the Nd³⁺ ions in Nd:GdCOB crystal.     

Transparent K2OTiO2P2O5SiO2 monolithic gels and inorganic amorphous solids through incomplete hydrolysis

Sol–gel derived transparent glasses are of technological interest because of its precisely controlled composition for multicomponent glasses at low temperature processing. The present work demonstrates a new and simple methodology for preparing transparent multicomponent oxide gels by incomplete hydrolysis of alkoxides. Through this processing, a small quantity of organic agencies resulted from incomplete hydrolysis of alkoxides self-disperses in inorganic oxide network, and thus control the formation of the monolith gel free of cracks. Specially, K₂OTiO₂P₂O₅SiO₂ gel monoliths have been synthesized through this route. The gels transformed into transparent K₂OTiO₂P₂O₅SiO₂ inorganic amorphous solids after heat treatment above 450 °C. This approach could be applied to many other multicomponent oxides.     

Characterization of deposits produced by TEA CO2 pulsed laser ablation of silicon mono- and dioxide

Silicon based deposits were prepared by TEA CO₂ pulsed laser ablation (PLA) of SiO and SiO₂ targets in the atmosphere of selected gases (N₂, He, Ne, Ar, Kr). These deposits possess high specific area of several hundreds m² per gram. Owing to the high specific area, some chemical groups and hydrogen related radical were detected by means of FTIR and EPR analyses and theoretical calculations: silyl (E′ center) Si, silylen Si:, silanon SiO, POL (peroxy linkage) SiOOSi and/or NBOHC (non-bridging oxygen hole center) SiO, POR (peroxy radical) SiOO and dioxysilirane Si(O)₂. In SiO₂ deposits the concentration of silyl Si resp. POR SiOO was determined to be 5.8 × 10¹⁸/g resp. 6.2 × 10¹⁹/g. In SiO deposits the ratio [Si:]:[Si] = (3.1-5.7) × 10¹⁹/g: (5.3-9.8) × 10¹⁹/g was measured. Estimated concentration of [Si] in deposits was increased nearly five times in comparison with SiO target. After exposure of the SiO deposits to H₂ EPR doublet with hyperfine splitting of 7.7 mT was observed. The best agreement between calculated theoretical and experimental values was found for the model [(HO)₃SiO]₂HSi. FTIR measurements and calculations of the silanol theoretical model clusters enabled us to discuss the chemical surroundings of the silanol and to determine the defects in the deposits.     

Optical and electrical properties of Be doped GaN bulk crystals

Highly resistive GaN : Be was obtained by means of synthesis of Ga+Be with atomic nitrogen under high nitrogen pressure. Activation energy of resistivity is about 1.5 eV. This material exhibits features very different from those observed in highly resistive bulk GaN : Mg. Up to 300 K strong yellow band dominates photoluminescence spectrum in resistive GaN : Be crystals. Positron annihilation studies point to the presence of gallium vacancies, V_Ga. In highly resistive GaN:Mg neither yellow band with considerable intensity, nor detectable concentration of V_Ga was found. We also discuss the puzzling findings in highly resistive bulk GaN : Be of morphological features typical for highly conducting bulk n-GaN material.     

Investigation of metal–GaN and metal–AlGaN contacts by XPS depth profiles and by electrical measurements

Metal/GaN Schottky contacts have been studied by X-ray photoelectron spectroscopy (XPS). Au/GaN, Pt/GaN, Pd/GaN are sharp while Ti/GaN is diffuse with the following composition, starting from the surface: Ti+TiN, Ti+Ti_xGa_yN, Ti+Ti_xGa_yN+Ga, GaN+Ga. Au/AlGaN and Ni/AlGaN contacts are much broader than Au/GaN: Al and Ga are found more than 100 Å away from the interface. Schottky barrier height was measured for the Au/GaN, Pd/GaN, Pt/GaN, Au/AlGaN and Ni/AlGaN contacts.     

Relationship between the short-range order and electrical resistivity in liquid indium-antimony

The composition dependencies of local structure and electronic structure, as well as the electric resistivity of liquid indium-antimony alloys have been investigated by the first-principles molecular dynamics simulations. It is shown that the variations of InIn, InSb and SbSb coordination tendency and the projected density of states of In and Sb in liquid In_xSb_1 ? x depend on the Sb concentration, and electric resistivity of liquid indium-antimony also reveals a regular change trends as a function of Sb concentration. Further analysis confirmed that there are explicit relationships between the short range structural parameters and electrical resistivities in liquid In_xSb_1 ? x.     

Erratum to:Microstructure and Rheological Behavior of Stabilized Gold Nanoparticles Hydrosol

Crystallography Reports - An Erratum to this paper has been published: https://doi.org/10.1134/S1063774521340010     

Radiation induced generation of non-bridging oxygen hole center in silica: Intrinsic and extrinsic processes

The generation of non-bridging oxygen hole center (Si–O) was investigated in a wide variety of natural (fused quartz) and synthetic silica samples exposed to different γ- and β-irradiation doses by looking at its optical bands. We distinguish two different generation processes: intrinsic associated with the cleavage of Si–O bond and characterized by a sublinear law and extrinsic due to the conversion of OH precursor characterized by a growth curve with a saturating tendency. The interplay between the two processes and the role of H are discussed.     

Effect of thermal annealing and hydrogen-plasma treatment in boron-doped microcrystalline silicon

We have investigated the effects of temperature (during film growth and post-deposition thermal annealing) and H₂-plasma treatment on the electronic and structural properties of p-type microcrystalline silicon films (p-μc-Si:H) for solar cell applications. The highest dark conductivity is obtained in the thermally annealed p-μc-Si:H prepared at low substrate temperature of 50 °C. This dark conductivity is decreased by two orders of magnitude when the film is exposed to H₂-plasma, being completely restored after thermal annealing. Namely, reversible dual-conductivity cycle is observed between thermally annealed state and H₂-plasma-treated state in p-μc-Si:H. The dual-conductivity cycle is accompanied with the reversible change in the infrared-absorption spectrum at around 1845 cm^? 1 assigned as SiHB complex in p-μc-Si:H network structure. Taking into account of the reversible structural change by H₂-plasma-exposure and thermal-annealing cycles, necessary process-procedure condition has been proposed for obtaining high photovoltaic performance in thin-film-Si solar cells with high quality p-μc-Si:H.     

Infrared attenuated total reflection spectroscopy studies of aprotic condensation of (EtO)3SiRSi(OEt)3 and RSi(OEt)3 systems with carboxylic acids

Aprotic hydrolysis and condensation reactions of bis end-capped trialkoxysilanes ((EtO)₃SiRSi(OEt)₃), linked via the organic chain R containing urea groups chemically bonded to a poly(propyleneglycol) (PPG) chain, in the presence of carboxylic acids, i.e. acetic-, chlorodifluoroacetic- and trifluoroacetic acids, were studied using infrared attenuated total reflection (IR ATR) spectroscopy. IR and ²⁹Si NMR spectral analysis revealed solvolysis reactions: the carboxylic acids interacted with ethoxysilane groups forming silyl esters leading to the formation of bridging SiOSi groups and carboxylic acid ester by-products. These results were compared with those obtained on simpler single capped methyltriethoxysilane (MeSi(OEt)₃, MTEOS) condensed with trifluoroacetic acid. Gelation of (EtO)₃SiRSi(OEt)₃ (catalyzed with acetic acid) encapsulated between a transparent conductive oxide (TCO) glass and a conductive and IR transparent silicon wafer was followed with the help of IR reflection–absorption spectroscopy. The results revealed that aprotic solvolysis of the hybrid precursor with acetic acid led to the formation of non-aqueous gels with low silanol content, confirming the advantages of aprotic solvolysis of organic–inorganic hybrids used as redox electrolytes in hybrid electrochromic (EC) and dye-sensitized photoelectrochemical (DSPEC) cells. Some comments regarding the accuracy of IR ATR spectral measurements compared to IR transmission spectra are also given.