Structural analysis of CaSiO3 glass by X-ray diffraction and Raman spectroscopy

The short-range structure of CaSiO₃ glass was studied by a combination of radial distribution analysis with an intensity comparison method on the basis of X-ray diffraction data. Three main peaks appeared at 1.64, 2.43 and 3.64 Å in the radial distribution function curve. The Raman bands were observed at 367, 642, 878 and 972 cm⁻¹ and the Raman spectrum was found to be similar to that observed in pyroxenes: single chains consisting of SiO₄ tetrahedra are linked by calcium ions laterally. The calcium ion is surrounded by six oxygen atoms at an average distance of 2.34 Å and the remainder Ca---O pairs at a distance of 2.54 Å. The calculated intensity curve based on this model was in good agreement with the observed one.     

An EXAFS study of Ag3AsS3 glass

The local structures of Ag₃AsS₃ glass at 80 and 300 K have been investigated by extended X-ray absorption fine structure analysis. By comparing the glass structure with that of Ag₃AsS₃ crystal (proustite), the possibility of ionic conduction by this glass is discussed. The local structure around an As atom in the glass is similar to that in the crystal. This fact suggest that, even in the glass structure, the As atoms from AsS₃ trigonal pyramids of shape similar to that in the crystal. The Ag---S distance (2.449 Å at 300 K) and the large root mean square displacement, σ, for the Ag---S atomic pairs in the glass, groups with a by the parameter fitting method, show that the Ag atoms are quite randomly distributed around the AsS₃ groups with a similar Ag---S distance to that in the crystal. Further, it is possible that the large thermal contribution to σ_Ag---S² for the glass may indicate the involvement of the Ag atoms in ionic conduction.     

A neutron diffraction investigation of the structure of vitreous boron trioxide

An extended review is given of previous structural work on vitreous B₂O₃ which comes to the conclusion that the best structural model comprises a mixed random network of boroxol groups and independent BO₃ triangles. The neutron scattering length for ¹¹B is slightly greater than that for oxygen so that neutrons should be more sensitive than X-rays to the presence of boroxol groups. Results are presented from a neutron diffraction investigation of vitreous ¹¹B₂O₃, using the Harwell linac pulsed neutron source, in which data have been obtained to high scattering vector values (Q_max=40 Å⁻¹) yielding good real space resolution. It is concluded that these data are consistent with a mixed boroxol group - independent BO₃ triangle network having 60% of the boron atoms in boroxol rings.     

An X-ray diffraction study of the structure of B2O3---Cs2O liquids

The short range structures of B₂O₃ (90 mol%)---Cs₂O (10 mol%) and B₂O₃ (80 mol%)---Cs₂O (20 mol%) liquids were analyzed at 973 and 1053 K, respectively, by an X-ray diffraction method, and the effects of Cs₂O addition on the boron-oxygen bonding were investigated. The existence of BO₃ triangles, which form the so-called boroxol ring structure, was confirmed in B₂O₃---Cs₂O liquids, as well as in B₂O₃ liquid, but some fraction of the BO₃ triangles was thought to be converted to BO₄ tetrahedra. Similar results have previously been observed also in B₂O₃---Cs₂O glasses. A Cs atom was found to be surrounded by six O atoms; four Cs---O interatomic distances were about 3.2 Å but the other two were at 3.8–3.9 Å. These distances indicate that distorted Cs---O octahedra may exist in these B₂O₃---Cs₂O liquids.     

An EXAFS study of the local structure of Ce---Si---O amorphous thin films

An EXAFS study has been made on the structure of three composition ranges of Ce---Si---O amorphous thin films prepared by RF sputtering. The measurements, carried out on the K edge of silicon and the L₃ edge of cerium, reveal that in the stoichiometric oxygen films of the general formula (Ce, Si) O₂, both cerium and silicon are four-coordinated by oxygen regardless of the O : Si ratio. In the oxygen-deficient films cerium remains four-coordinated by oxygen, but, around silicon, the oxygen atoms are progressively replaced by silicon as the oxygen content of the films is reduced. In silicon-rich films which are very deficient in oxygen, the oxygen atoms prefer to ramain coordinated with cerium, rather than silicon.

A definite decrease in the Si---O distance with increase in Si---O coordination has been found. The effect is attributed to an increase in the charge of silicon with oxygen coordination, and supports a randomly bonded model for the structure.

The total oxygen coordination, derived from a consideration of bond conservation, indicates that the film structures are probably SiO₂-type continuous random networks.     

Crystal growth and structure of MnGa2Te4

Single crystals of MnGa₂Te₄ were grown from the melt using the directional freezing technique. They crystallize in the monoclinic system, a=11.999(3), b=11.999(3), c=24.922(6) Å, β=104.01(2)°, Z=16 MnGa₂Te₄ units, space group C2/c. The structure was solved by direct methods and refined to R_w=0.035 for 791 observed reflections and to R_w=0.062 for 3067 independently measured reflections. Te atoms form an arrangement which is a superlattice of anion lattice of β-Cu₂HgI₄. On the contrary, the same model does not conform cation lattice, because 1/3 of metal atoms occupy positions displaced from tetrahedral sites.     

XAS study of lanthanum coordination environments in glasses of the system K2O---SiO2---La2O3

The La L₁ and L₃ XANES and L₃ EXAFS have been investigated for the series of glasses 10K₂O---50SiO₂---x La₂O₃ (x = 1, 5, 10) and (10 − x)K₂O---40SiO₂−(x/3)La₂O₃ (x = 7.5, 5, 2.5) and model compounds La₂O₃, LaAlO₃, LaPO₄, La₂NiO₄, La₂CuO₄ and La(OH)₃. An edge resonance at 25 eV above the L₁ edge in the glass spectra is concentration-dependent, decreasing in intensity with increasing lanthanum concentration. The 2s → nd forbidden transition increases with La₂O₃ concentration, indicating a reduction in the ‘average’ site symmetry of the first coordination shell of La. Mapping _X(k) space, which is a new and promising technique, was employed to extract bond distance, coordination number and thermal parameters from the EXAFS. By this method, one calculates the complete _X(k) space a function of all physically reasonable values of the adjusted parameters in all possible combinations. The advantage in this method is the assurance of a global minimum. Bond lengths were comparable to those obtained by Fourier transforming the phase corrected EXAFS. The values are 2.42 Å (± 0.03 Å) for La---O. The coordination numbers (N ≤ 7 ± 1.5) were derived by mapping and comparison to the published structures for other La compounds. _X(k) mapping is compared with least-squares fitting the data, and the correlation between the Debye-Waller factor and coordination number is also discussed.     

A comparison of the medium-range order in glassy GeS2 and Sb2S3

In amorphous (a-) GeS₂ there is only one medium-range order (MRO) dependent X-ray scattering feature, i.e., the ‘first sharp diffraction peak’ (FSDP), whereas in a-Sb₂S₃ all scattering features in the interval 1–2.4 Å⁻¹ are in fact MRO-dependent. The basic element of MRO in a-GeS₂ is a part of a chain of corner bound tetrahedra extracted from the high temperature form of c-GeS₂; in a-Sb₂S₃ it is a part of a crystalline-like (Sb₂S₃)_n band. Ordering of parts of these bands is characterized by a greater interband separation than in the crystal. By contrast with a-GeS₂, the MRO-dependent medium-angle scattering features in a-Sb₂S₃ are less sensitive to fluctuations of the interband (intercluster) ordering distance.     

Synthesis, thermal and magnetic properties of new metal iodate: (LiFe1/3)(IO3)2

This paper reports the detail synthesis of a new kind of metal iodate, anhydrous (LiFe_1/3)(IO₃)₂, from aqueous solutions. The synthesized compound shows spinal morphology and is chemical stable up to 400°C. The iodate shows paramagnetic behavior from room temperature down to 4.2 K. At room temperature, the new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1, space group of P6₃.     

EXAFS studies of arsenic in amorphous silicon

Extended X-ray absorption fine structure measurements were used to determine nearest neighbor coordination numbers and distances for As in amorphous Si prepared by 100 keV As ion-implantation of single crystal Si. In the limit of low As concentration, the average As---Si coordination number was 3.2±0.1 and the As-to-Si distance was 2.37±0.02 Å, compared with 4 and 2.41±0.02 Å, respectively, for As in crystalline Si. It is concluded that 20% of the As atoms are fourfold coordinated and 80% are threefold coordinated in the amorphous Si, and that the lack of electrical doping by the fourfold coordinated As results from electron trapping by dangling bonds or other structural defects.     

EXAFS and XANES joint analyses for semiconducting vanadium phosphate glasses

Vanadium EXAFS spectra of 50V₂O₅-50P₂O₅ glasses with different C = V⁺⁴/V_tot have been measured. The V-O distances increase by ΔR₁ = (0.03 ± 0.02) Å to ΔR₂ = (0.07 ± 0.03) Å going from a glass with C = 0.64 to C = 0.84 and from C = 0.51 to C = 0.84, respectively. The EXAFS data show a basically similar structure of the vanadium sites for both the V⁴⁺ and V⁵⁺ ionic states. The density of the glasses increases with C from the value d₁ = 2.81 g/cm³ for C = 0.51 to d₂ = 2.92 g/cm³ for C = 0.84 indicating a more random packing of glass units.     

A simple method to synthesize single-crystalline β-wollastonite nanowires

The single-crystalline β-wollastonite (β-CaSiO₃) nanowires were prepared via a simple hydrothermal method, in the absence of any template or surfactant using cheap and simple inorganic salts as raw materials. Xonotlite [Ca₆(Si₆O₁₇)(OH)₂] nanowires were first obtained after hydrothermal treatment at a lower temperature of 200 °C for 24 h, and after being calcinated at 800 °C for 2 h, xonotlite nanowires completely transformed into β-wollastonite nanowires and the wire-like structure was preserved. The synthesized β-wollastonite nanowires had a diameter of 10–30 nm, and a length up to tens of micrometers, and the single-crystalline monoclinic parawollastonite structured β-wollastonite was identified by XRD with the space group of P2₁/a and cell constants of a=15.42 Å, b=7.325 Å, c=7.069 Å and β=95.38°. A possible growth mechanism of β-wollastonite nanowires was also proposed. The advantages of this method for the nanowire synthesis lie in the high yield, low temperature and mild reaction conditions, which will allow large-scale production at low cost.     

Structure of a copper sodium phosphate glass by neutron scattering with isotopic substitution

The structure of a sodium copper phosphate glass containing approximately equimolar concentrations of CuO, Na₂O and P₂O₅ (0.3CuO·0.35Na₂O·0.35P₂O₅) was studied. From the total structure factor, the oxygen environment of P and Cu can be established. The first- and second-neighbour environment of Cu can be measured more accurately by taking first differences between the normalised scattering intensities for specimens containing ⁶³Cu and ⁶⁵Cu. The first-neighbour shell is found to be narrow with a mean radius of 0.2 nm - almost identical to the value found in similar crystals and with a coordination number of 4.0 (as in the crystal). Further oxygens are observed at about 0.25 nm, suggesting that the shell exhibits Jahn-Teller distortions, again as in the crystal, where two atoms are found at the longer distance. The Cu---Cu distribution has been measured directly using second difference techniques. The Cu---Cu signal is extremely weak - due to the low Cu concentration (about 7%) but a peak near 0.6 nm is observed. This corresponds to the mean distance calculated for a random dispersion of Cu atoms in the glass but the peak is so narrow that the Cu environment is clearly not random. In particular, it is possible that the Cu is ‘solvated’ by a shell of Na---O polyhedra.     

Laser heated pedestal growth of orthorhombic SrHfO3 single crystal fiber

SrHfO₃ single crystal fibers were grown by the laser heated pedestal growth technique. These fibers have orthorhombic symmetry with lattice parameters of a=5.773(1) Å, b=5.764(3) Å, c=8.157(2) Å at 300 K.     

手性镝(III)-酒石酸配合物的合成、单晶转换及热稳定性研究

以2,3-二乙酰对甲苯-D-酒石酸(D-H₂DTTA)为原料,与金属Dy(III)盐反应,经过单晶-单晶转换,得到一种新的酒石酸(H₂tar)配合物[Dy(Htar)₃(H₂O)₃]_n(1),对该配合物用元素分析、红外光谱、X-射线单晶衍射、粉末衍射以及差热-热重等进行了表征。晶体结构分析表明,配合物1属三方晶系,R3空间群,晶胞参数为a=b=2.723 16(14) nm,c=0.762 75(6) nm,α=β=90.00°,γ=120.00°,V=4.898 5 (6) nm³,Z=3, 剑桥晶体数据库(Cambridge Crystallographic Data Centre, CCDC)编号为1498504。配合物中的金属Dy³⁺分别与三个酒石酸离子配体Htar^-上的六个氧原子和三个配位水分子上的三个氧原子配位,形成九配位三帽三棱柱构型。配合物1在c方向上通过O1和O5原子连接成一维链状结构,相邻Dy³⁺之间的距离为0.762 8(1) nm。配合物1是由[Dy(HDTTA)₃(CH₃OH)₃]_n经单晶-单晶转换过程得到,其转换过程包括酯基水解及水分子取代两类反应。配合物1具有一定的热稳定性,45~166 ℃失去配位水分子,高于166 ℃配合物骨架坍塌。     

TEM investigation on the structure of amorphous silicon monoxide

Commercially available powder samples of silicon monoxide have been investigated by methods of transmission electron microscopy: electron scattering, electron energy-loss spectroscopy (EELS) and electron spectroscopic imaging (ESI). Pair distribution functions (PDFs) as well as EEL spectra can be shown to be a composition of the PDF and EEL spectra of elemental silicon and amorphous SiO₂. The distribution of the elements silicon and oxygen calculated from ESI images proof the silicon monoxide to be inhomogeneous, i.e. it consists of amorphous silicon and amorphous SiO₂. The phase separated regions measure ≈3–4 nm. One maximum in the PDF at 2.95 Å does not stem from either a-Si or a-SiO₂, and it is assigned to atomic configurations at the interphase boundary layer between Si and SiO₂. The portion of the interphase domain in the total composite material is estimated to be between 20% and 25%.     

New organic nonlinear optical crystals of indole-3-aldehyde

Indole-3-aldehyde (IA) with powder second harmonic generation (SHG) efficiency 38 times as large as that of KDP and cutoff wavelength of 340 nm is reported. The method of solvent evaporation was used to grow IA crystal. High quality single crystals with dimension of 18x8x35 mm³ were obtained. IA crystal belongs to the orthorhombic system space group Pca2₁, and the unit cell parameters are: a = 14.154(3) Å, b = 5.836(2) Å, and c = 8.724(4) Å.     

X-ray diffraction measurements for liquid As2Se3 up to the semiconductor-metal transition region

X-ray diffraction measurements were performed for liquid (1-) As₂Se₃ at temperatures and pressures up to 1500°C and 70 bar. A high-pressure vessel and a sapphire sample cell were developed, according to the authors' own design, for measurements using the energy-dispersive method. The structure factor becomes broadened with increasing temperature and changes significantly at about 1000°C accompanied by the semiconductor-to-metal (SC-M) transition; the first sharp diffraction peak around 1.2Å⁻¹ disappears and the second and third maxima merge. The nearest-neighbor distance and the average coordination number start to increase when the SC-M transition occurs. The density of 1-As₂Se₃ in the temperature and pressure range up to 1600°C and 700 bar, respectively, were also measured by the X-ray absorption method. A volume contraction occurs in the SC-M transition region.     

X-ray diffraction study on amorphous gallium

Amorphous films of some μm in thickness, prepared by low temperature condensation in an ultra-high vacuum onto liquid helium cooled substrates, have been studied in situ by using an X-ray diffractometer operating in a symmetrical reflection mode. The structure factor of gallium has been obtained over the wavevector range 1.3 to 16.1 Å⁻ by means of two wavelengths, Cr_K and Mo_K, monochromatized by balanced filters. The average number of nearest neighbours deduced from the well-resolved first maximum in the radial distribution function is equal to 9.3 atoms. The results are compared to those previously found by electron diffraction measurements on thin films and also to the structure of supercooled liquid.     

The stability and surface reactivity of gallium phosphide nanocrystals

The stability and surface reactivity of Gal? nanocrystals were characterized by TG-DTA, XRD and XPS measurements. The samples were heated in O₂ and N₂ atmospheres respectively. The experimental curve which describes the mass change as a function of temperature shows that the mass decreases under 330°C but increases in two stages between 33°C and 550°C. The curves obtained in O₂ and N₂ are obviously different. The results of XPS indicate that the density of oxygen atoms bonded chemically to the gallium atoms on the surface increases when the sample is heated in O₂ up to 200°C, whereas the density of nitrogen atoms increased when heated to 330°C in N₂. It can be concluded that the N₂ could be activated on the surface of GaP nanocrystals at a rather low temperature, and highly reactive nitrogen atoms formed. Our result obtained makes it possible to synthesize a series of nitrogen-containing compounds in N₂ gas under moderate conditions.