Crystal structure of synthesized CuGa0.5In0.5Te2 determined by X-ray powder diffraction using the Rietveld method

A full profile X-ray powder diffraction structure refinement has been carried out on a sample of synthesized CuGa_0.5In_0.5Te₂ using graphite monochromatized CuK step-scan data and a profile shape of the Pearson VII type. The most satisfactory convergence was achieved atR _P=0.0483,R _WP=0.0641,R _B=0.0208 andR _F=0.0320, where,R is the Rietveld refinement. The derived structural parameters at 26 °C area=0.610 09(2) nm,c=1.219 79(4) nm andx [Te]=0.2279(3). The ratio between lattice parameters, =c/2a=0.9997 (0) differed very slightly from 1, while the non-ideal anion displacements,x [Te] 1/4, was manifested by the existence of bond alternation of Cu-Te, Ga-Te and In-Te.     

Crystal structure refinement of A-type carbonate apatite by X-ray powder diffraction

Complete carbonate substitution at A-sites (OH) of low-crystallinity hydroxyapatite with near stoichiometric composition (i.e. Ca/P ratio of 1.65) was achieved by heating in a dry carbon dioxide flow at 1173 K for 64 h. The carbonate content was analysed by thermogravimetry and infrared absorption spectrometry; the chemical composition was determined to be Ca_9.9±0.1(PO₄)_6.00±0.1(CO₃)_0.9±0.1. The crystal structure and atomic configuration of the carbonate ion were determined by Rietveld refinement using X-ray powder diffraction data. This analysis revealed that the space group was monoclinic Pb with a = 0.9571(1), b = 1.9085(2), c = 0.68755(3) nm and γ = 119.847(7)°. The triangular planes of the carbonate ions were oriented parallel to the c- and a-axes, though there were two independent carbonate sites with occupancy factors of 0.56(1) and 0.34(1), where the triangles were oppositely rotated about the corresponding carbon atoms by 23° and −18°, respectively. The arrangement of the ions was disordered, which explains the lack of a thermal phase transition below 623 K.     

Crystal structure and spontaneous magnetism of BiFeO3 powder synthesized by hydrothermal method

Single-phase BiFeO3 powder was successively synthesized by a low-temperature hydrothermal method. Scanning electron microscopy and transmission electron microscopy results showed that BiFeO3 powder had several hundred nanometers to micrometer-sized particles with a broad size distribution. BiFeO3 powder showed weak-ferromagnetic behavior with a small magnetization value (Ms approximately 20 memu/g) at room temperature. Rietveld refinement results for the crystal structure show the displacive disorder of the Fe-site(6a); the Fe-site(6a) splits into two pairs, Fe(1) and Fe(2) displaced by 0.9 angstroms from each other and these sites are partially occupied. Hence the O-site(18b) also splits into the two partially occupied sites forming a distorted FeO6 octahedras. The weak ferromagnetism observed in the hydrothermal BFO powder is ascribed to the displacive disorder of FeO6 octahedras resulting in an incomplete counterbalance between the antiferromagnetic sublattices of the Fe-ions.     

Crystal structure of dense pseudo-cubic boron allotrope, pc-B52, by powder X-ray diffraction

During past years, a number of reports have been published on synthesis of tetragonal allotrope of boron, t-B₅₂ phase. However, no unambiguous characterization of the crystal structure has been performed to the present time, while remarkable variation of the a/c lattice-parameter ratio raises strong doubts about its uniqueness. Here the Rietveld refinement of the crystal structure of the high pressure-high temperature boron phase synthesized by a direct solid-state transformation of rhombohedral β-B₁₀₆ at 20 GPa and 2500 K has been reported for the first time. Although this boron allotrope belongs to the t-B₅₂ type, its structure can be considered as pseudo-cubic with the a/c ratio of $\sqrt 2 $ .     

A study of structural transition in nanocrystalline titania thin films by X-ray diffraction Rietveld method

Structural and microstructural analyses of nanocrystalline titania thin films prepared by pulsed laser deposition have been carried out. At lower oxygen partial pressures (≤10⁻⁴ mbar), rutile films were formed, whereas at 1.2 × 10⁻³ mbar of oxygen partial pressure, the thin films contained both rutile and anatase phases. At 0.04 and 0.05 mbar of oxygen partial pressure, the film was purely anatase. Addition of oxygen has also shown a profound influence on the surface morphology of the as deposited titania films. Modified Rietveld method has been used to determine crystallite size, root mean square strain and fractional coordinates of oxygen of the anatase films. The influence of crystallite size and strain on the rutile to anatase phase transition is investigated.     

X-ray diffraction Rietveld analysis of cold worked austenitic stainless steel

In the present study, the dislocation density of cold worked austenitic stainless steel samples in the range 2-40% was calculated on the basis of Williamson-Smallman approach using modified Rietveld method. Dislocation density has been found to increase significantly with increasing percentage of cold work up to 20%. The dislocation density is found to be 1.8 × 10¹¹/m² for the annealed sample and are 3.6 × 10¹⁵/m² and 5.4 × 10¹⁵/m² for 20% and 40% cold worked sample, respectively. The effect of cold work on dislocation density, hardness and Fourier electron density of the cold worked samples is discussed in comparison with the annealed sample.     

XRD衍射分析评估锂镍镁氧化合物的合成

锂离子电池,又被称作"摇椅电池",具有体积小、质轻的特点;理论容量高达274mAh/g的正极材料LiNiO2极受研究关注,以镁掺杂锂镍氧化物,能有效提高充放电循环稳定性,并于Li+脱嵌时提供支柱作用(pillaring effect),因之少量掺镁可有效改进LiNiO2之电化学性能.本实验以XRD依据I(003)/I(104)峰比值、R-factor(I(006)+I(102))/I(101)峰比值、I(108)与I(110)的峰分裂,探讨在不同煅烧温度、煅烧时间、升温速率、试样压片的压强大小、气氛等变数条件所合成之锂镍镁氧化物LiNi0.95Mg0.05O2.发现以210～280 MPa对试样压片,在氧气气氛下经2℃/min升温速率升温至600℃,预烧9～15h后,再粉碎、压片以5℃/min升温至600℃之后以1℃/min升温至750℃恒温15～20h,可得I(003)/I(104)峰比值1～1.1,R-factor(I(006)+I(102))/(101)峰比值0.67～0.94,并且有(108)与(110)的分裂峰,同时c/a比值4.914～4.925,属于R3m空间群的锂镍镁氧化合物.     

X射线粉末衍射数据的校正

扼要介绍了X射线粉末衍射数据（峰位峰强和峰形）的校正方法和使用的标样。     

The polymorphs of zirconia: phase abundance and crystal structure by Rietveld analysis of neutron and X-ray diffraction data

Rietveld analysis of neutron and X-ray powder diffraction data has been used to obtain the crystallinity and relative abundances of cubic (22 at% Y), tetragonal (5.8 at% Y), and monoclinic zirconia in synthetic binary and ternary mixtures of the pure phases. The stabilized cubic and tetragonal forms are shown to be 94 (2) and 96 (2)% crystalline, respectively, but no amorphous material was detected in the chemically pure monoclinic phase. In both stabilized polymorphs, the yttrium atoms randomly substitute into the zirconium site, with a charge-compensating proportion of vacancies on the oxygen atom site. In this near worst-case situation of very similar cubic and tetragonal unit cell dimensions, the phase abundances determined by Rietveld analysis of neutron data are very accurate and superior to those determined by integrated-intensity methods of analysis. For X-ray data, the accuracy is diminished by the presence of extinction, and by uncertainty in the definition of the peak shape of the cubic phase due to the absence of intense high-angle reflections and the resultant dependence on strongly overlapping low-angle data. On leave from: CSIRO Mineral Products, POB 124, Port Melbourne, Victoria 3207, Australia     

Stress in hydrogenated amorphous silicon determined by X-ray diffraction

The residual strain in an a-Si:H layer has been directly determined with X-ray diffraction techniques from variations in the diffraction angle of the first amorphous peak using CuK radiation. The layer was deposited by HW-CVD on glass substrates at a growth temperature of 300 °C, and is known from previous studies to be highly disordered. It was found to have an average compressive stress of 750 MPa, using the c-Si lattice parameter as a reference, and typical values of the elastic constants for a-Si:H, increasing strongly towards the surface.     

Structural strain in pyrites evaluated by X-ray powder diffraction

Two parameters for measuring the structural strain, the effective Debye-Waller parameter, B _eff, and lattice strain, , were evaluated on a natural pyrite (FeS₂) after grinding. The effective Debye-Waller parameter, B _eff, which depends on the displacement of atoms in the crystal, was calculated for the overall crystal, B _eff(FeS₂), and for sulphur, B _eff(S), from the intensities of the X-ray diffraction lines. The B _eff(S) increased markedly with increasing grinding time, while B _eff(FeS₂) did not change significantly. The lattice strain, , was not recognized. These observations suggest that the displacement of sulphur atoms preferentially takes place by grinding. The relations between these B _eff values and crystallite size, L, were observed to be common for two different methods of grinding. This tendency was considered to be an inherent property of pyrite. The value of B _eff(S) is a useful index to estimate mechanically caused strain in pyrite.     

Crystal structure of a high-pressure/high-temperature phase of alumina by in situ X-ray diffraction

Alumina (alpha-Al(2)O(3)) has been widely used as a pressure calibrant in static high-pressure experiments and as a window material in dynamic shock-wave experiments; it is also a model material in ceramic science. So understanding its high-pressure stability and physical properties is crucial for interpreting such experimental data, and for testing theoretical calculations. Here we report an in situ X-ray diffraction study of alumina (doped with Cr(3+)) up to 136 GPa and 2,350 K. We observe a phase transformation that occurs above 96 GPa and at high temperatures. Rietveld full-profile refinements show that the high-pressure phase has the Rh(2)O(3) (II) (Pbcn) structure, consistent with theoretical predictions. This phase is structurally related to corundum, but the AlO(6) polyhedra are highly distorted, with the interatomic bond lengths ranging from 1.690 to 1.847 A at 113 GPa. Ruby luminescence spectra from Cr(3+) impurities within the quenched samples under ambient conditions show significant red shifts and broadening, consistent with the different local environments of chromium atoms in the high-pressure structure inferred from diffraction. Our results suggest that the ruby pressure scale needs to be re-examined in the high-pressure phase, and that shock-wave experiments using sapphire windows need to be re-evaluated.     

Rietveld X-ray diffraction analysis of nanostructured rutile films of titania prepared by pulsed laser deposition

Rietveld powder X-ray diffraction analysis of the rutile films of titanium oxide prepared by pulsed laser deposition was carried out. The crystallite size increased with increase of substrate temperature, while the strain showed a reverse trend. The films synthesized at temperature ≥573 K showed that the crystal structure was almost close to that of bulk rutile structure. The influence of the substrate temperature on the lattice parameters and oxygen coordinates were also studied in the present work.