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New compounds Li6MB3O9 (M=Nd,Sm,Eu,Tm,Er) were synthesized by solid-state reaction. The crystal structure of Li6NdB3O9 was analyzed from both powder and single crystal X-ray diffraction data. The results obtained by powder diffraction analysis and Rietveld refinement are a=7.2725(4) Å, b=16.6398(9) Å, c=6.7529(5) Å, β=105.398(8)°, and space group P21/c, which agree with the results obtained by single crystal diffraction analysis: a=7.2712(4) Å, b=16.6268(9) Å, c=6.7484(4) Å, β=105.411(1)°, and space group P21/c. This compound is isostructural with Li6YB3O9. Single crystal structure analysis showed that the fundamental building unit of these isostructural compounds comprises three isolated [BO3]3− triangles, one distorted [NdO8]13− triangulated dodecahedron, four distorted [LiO5]9− five-coordinated polyhedra, and two [LiO4]7− tetrahedron. An analysis of the infrared spectrum of Li6NdB3O9 confirmed the presence of isolated [BO3]3− triangles in Li6NdB3O9. The remaining four Li6MB3O9 (M=Nd, Sm, Eu, Tm, and Er) compounds were found to be isostructural with Li6NdB3O9. Their unit cell dimensions decrease with an increase in the atomic number of the rare-earth atoms. DTA and TGA measurements of Li6MB3O9 (M=Nd, Sm, Eu, Tm, and Er) revealed that these borates congruently melt from 800 °C to 860 °C.
A synthetic analogue, Ca(Ti0.6Al0.2Sb0.2)OSiO4, of antimony-bearing titanite of a composition similar to that found at St. Marcel-Praborna (Italy) was synthesized using ceramic methods and the crystal structure was refined using the Rietveld method. Unit-cell dimensions (in Å) are a=7.0184(1), b=8.7097(2), c=6.5586(1), and β=113.700(1)°. The substitution of 40% Ti by (Al+Sb) in octahedra causes a loss of long-range coherency of the off-centered Ti atoms. The space group of Sb-bearing titanite is A2/a, like other cases of M3+-M5+-doped titanites. This study confirms that titanite with up to 0.2 Sb atom per f.u. can exist and that the substitution scheme is 2Ti4+↔Al3++Sb5+.
Manganese molybdate with the formula Mn2MoO5.0.6H2O was synthesized by hydrothermal reaction at 200 °C. The crystal system of this compound is triclinic, space group P−1, Z=1, unit-cell parameters: a=5.7769(5), b=9.7559(6), c=2.8961(2), α=94.37(1), β=101.37(1), and γ=94.75(1). The measured density (Dm) and calculated density (Dx) are 3.200 and 3.103, respectively.
Differences between up-cut and down-cut grinding are usually not considered since both modes are alternating during conventional face grinding. Nevertheless, there is a pronounced distinction in the fashion of material removal which could lead to unequal states of surface residual stress. By means of X-ray diffraction analysis, ground plates made from three types of steel were investigated in order to compute and compare both macroscopic and microscopic residual stress and domains of coherent scattering. With respect to the main sources of residual stress generation, i.e., plastic and thermal deformation, machining process was carried out in two types of cooling environment. The results indicate significant influence of heat removal since differences between the two grinding modes are virtually nonexistent for liquid cooling, whereas dry grinding results in higher compressive normal residual stresses for down-cut mode in comparison to the up cut.
Synthesis and structure of two phosphates belonging to the ternary Sb2O5–In2O3–P2O5 system are realized. Structures of SbV1.50InIII0.50(PO4)3 and (SbV0.50InIII0.50)P2O7 phases, obtained by solid state reaction in air at 950 °C, were determined at room temperature from X-ray powder diffraction using the Rietveld method. SbV1.50InIII0.50(PO4)3 have a monoclinic (space group P21/n) distortion of the Sc2(WO4)3-type framework. Its structure is constituted by corner-shared SbO6 or InO6 octahedra and PO4 tetrahedra. Monoclinic unit cell parameters are a=11.801(2) Å, b=8.623(1) Å, c=8.372(1) Å, and β=90.93(1)°. (Sb0.50In0.50)P2O7 is isotypic with (Sb0.50Fe0.50)P2O7 and crystallizes in orthorhombic system (space group Pna21) with a=7.9389(1) Å, b=16.0664(2) Å, and c=7.9777(1) Å. Its structure is built up from corner-shared SbO6 or InO6 octahedra and P2O7 groups (two group-types). Each P2O7 group shares its six vertices with three SbO6 and three InO6 octahedra, and each octahedron is connected to six P2O7 groups.
Crystalline phases present in pigments scratched off the surfaces of some decorated ceramic sherds belonging to the Cucuteni Neolithic culture were successfully identified using synchrotron radiation X-ray diffraction at Daresbury Laboratory. The ceramic sherds were selected from a collection of the National Museum of Romanian History in Bucharest. The synchrotron radiation X-ray diffraction analysis revealed that the black-color pigments on the surface of a number of sherds were produced by a variety of jacobsite (Fe2MnO4) phases; magnetite (Fe3O4) was also found in one of the sherds. The red color was derived from clay slips with a high content of hematite (Fe2O3). Calcite (CaCO3) was found in the white pigments; its presence was explained as being related to postburial deposition processes. Conclusions on technological aspects, provenance, and conservation issues are given.
A natural sodalite from the geological site Alkaline Complex of Floresta Azul, Bahia, Brazil, has been characterized by electron microprobe, infrared spectroscopy, and powder high-resolution X-ray diffraction techniques. The mineral is an aluminosilicate framework, formed by cages called sodalite unity. Although the sample is natural, the chemical analysis reveals that it is indeed the end member sodalite sensu strictu, Na8[Si6Al6O24]Cl2. Infrared spectroscopy shows Si, Al tetrahedral-oxygen stretching nonsymmetric mode, stretching symmetric mode, and bending modes. Indexing of the experimental X-ray diffraction pattern led to cubic space group P-43n, and unit-cell parameters: a=8.8767(7) Å, Dx=2.301 g cm−3, and V=699.46(1) Å3. X-ray diffraction data are reported. Rietveld refinement was also performed, and the confidence factors are Rp=0.079, Rwp=0.118, and χ2=2.19. The structure of the minerals of sodalite group holds four different tetrahedra: AlO4, ClNa4, Na(ClO3), and SiO4, with Al, Cl, Na, and Si located at the center of each tetrahedron.
Without experimental or predicted literature crystal structures for succinonitrile at low temperature, structure solution was attempted from powder diffraction data taken at 173 and 90 K from a solid sample. Its room-temperature plastic-crystal state makes production of a sample with good particle statistics and random orientation almost impossible. Combining constrained models, simulated annealing, and careful application of second-order spherical harmonic corrections nevertheless produced viable-looking structures at 90 and 173 K, yielding two distinct structure models with the same projection down c. VASP optimization of atom coordinates in the experimental cell agreed well with the 90 K model but poorly with the model derived from the 173 K data. The refined 90 K structure changed little on optimization and fitted all datasets from 85 to 225 K. Plots of cell data, torsion angles, and isotropic displacement parameters against temperature suggest possible phase transitions around 100, 120, and 180 K. Cell data at 90 K: monoclinic P21/a, a=9.0851(5) Å, b=8.5617(5) Å, c=5.8343(3) Å, β=79.295(2)°, and Z=4. Succinonitrile has gauche conformation, in agreement with literature spectroscopy data.
It is demonstrated that a complex X-ray characterization of semiconductor films epitaxially grown on metal oxide buffer layers and Si(111) substrates is possible using laboratory-based equipment. This is demonstrated with epi-germanium on Pr2O3 as buffer material. Pole figure measurements prove that epi-Ge layers are nearly single crystalline with exactly the same in-plane orientation (type A) as the Si(111) substrate, while the lattice of the oxide layer is 180° rotated around the [111] surface normal (type B). Only a small fraction (less than 0.6 vol %) of the epi-Ge exhibits type B rotation twins. The main structural defects are microtwin lamellas lying in {111} planes 70.5° inclined to the wafer surface. The different in-plane orientation of the Si substrate and epi-Ge on one side and the Pr2O3 buffer layer on the other side allows a very sensitive analysis of strain and defects even for a 10-nm oxide layer buried under a 100-nm Ge. The epi-Ge layers are nearly fully relaxed and the Pr2O3 buffer layer is compressively strained. Due to the existing defects the Ge (111) planes are tilted in a characteristic pattern relative to the Si substrate.
This study focuses on characterization of an (Al,Cr)3Ti alloy processed together with titanium powder by reactive mechanical milling (RMM) to produce an ultrafine grained intermetallic alloy matrix with in situ carbide and hydride phases formed during processing. Observations of X-ray scattering as RMM processing time increases show severe broadening of matrix diffraction peaks, accompanied by the appearance of diffraction peaks resulting from the formation of very small crystallites of TiC and TiH1.92 phases with increasing volume fractions, and finally, increasing background intensity as the crystallite size of the matrix phase decreases to ∼2 nm. Estimates of phase volume fractions were made by the direct comparison method, along with crystallite sizes by Warren–Averbach peak profile analysis. The general increase in background intensities has been attributed to random static displacements of the large fraction of atoms located within the grain boundary regions. Further, it has been concluded that the matrix material with a crystallite size of a few nanometers has about half the atoms in statically displaced positions defining the boundary regions. The results argue that background intensity changes should not be ignored and are useful in interpreting scattering from these nano-scale materials.
The ICDD sponsored a round robin on the quantitative Rietveld phase analysis of pharmaceuticals. 11 participating laboratories from the pharmaceutical community submitted both raw data and processed quantitative results. The purpose of the round robin was to evaluate current practices in laboratories, so procedures and methods were not specified, but they were recorded. Cluster analysis tools were applied to all the data sets and their use helped identify the root causes of several types of errors in specimen preparation, data treatment, and Rietveld analysis. The authors considered this round robin to be difficult. Sample homogeneity was an issue and molecular orientation was observed in many data sets. Each material studied has structural polymorphs so the selection of starting parameters and their refinement was nontrivial. Similar to prior round robins on inorganic materials and minerals, this round robin identified operator errors as the major contributor to poor results. Four laboratories achieved excellent results on all phases in all three samples, with accuracy within relative errors of 5% to 10%.