Calibration of powder diffraction experiments using area detectors is essential to extract high quality one-dimensional powder diffraction pattern. Precise calibration necessitates a sensible characterization of the Debye-Scherrer rings formed on the detector plane. An algorithm, designed and developed to automate this process, is described in this paper. All the parameters required for an experimental calibration are extracted using robust pattern recognition techniques. Several image preprocessing methods are employed, reducing the computational cost but retaining high signal quality. A modified version of a one-dimensional Hough transformation is used to determine the final parameters of the ellipses. After extraction, the parameters are optimized using nonlinear least squares fit. The presented algorithm is insensitive to image artefacts and was successfully applied to a large number of calibration images. The performance of the algorithm is demonstrated by the comparison of results obtained from the presented automatic calibration method and an existing manual method.

X-ray diffraction pattern from cotton fiber (dch32) grown in the Karnataka state of India has been recorded. Fiber was found to contain 17 Bragg reflections, of which 11 are broadened because of crystal size and intrinsic strain influences. Contributions to integrated intensities from intrinsic strain in the fiber have been estimated using line profile analysis. A molecular model was first constructed with standard bond lengths and angles using helical symmetry and layer-line spacings observed in the X-ray pattern. The model was then refined against observed X-ray data using the linked atom least squares (LALS) method. The refinement has been done with and without the intrinsic strain correction to find the extent of structural changes. These changes have been quantified in terms of bond angles, bond lengths, and torsion angles. Young’s modulus has been estimated for these fibers using the results of line profile analysis, and a broad agreement with the reported physical measurements has been obtained.

A new structural model is proposed for cubic nitroprussides and the crystal structure for the complex salts of Fe(2+), Co(2+), and Ni(2+) refined in that model. In cubic nitroprussides the building unit, [Fe(CN)5NO]2−, and the assembling metal (M=Fe2+,Co2+,Ni2+), have ¾ occupancy with three formula units per cell (Z=3). This leads to certain structural disorder and to different local environments for the outer metal. The crystallographic results are supported by the Mössbauer and infrared data. The XRD powder patterns, index in a cubic cell (Fm3m space group), show a sinuous background because of diffuse scattering from positional disorder of the metal centers. Because of this, the crystal structures were refined allowing the metal centers to move from the (0,0,0) and (0,0,1/2) positions (away from positional symmetry restrictions). The refinement under these conditions leads to excellent agreement factors (Rwp, Rp, S), good pattern background fitting, and produced a refined structural model consistent with the crystal chemistry of nitroprussides. The studied materials are obtained as hydrates. On heating, the crystal water evolves, and below 100°C an anhydrous phase is obtained, preserving the framework of the original hydrates. The loss of the crystal water leads to cell contraction that represents around 2% of cell volume reduction. On cooling down from room temperature to 77 and 12 K, a slight expansion for the -M-N≡C-Fe-C≡N-M- chain length is observed, suggesting that at low temperature and reduction in the metals charge delocalization on the CN bridges takes place. For M=Fe and Co the crystal structure was also refined for the anhydrous phase at 12, 77, and 300 K.

A polycrystalline sample of YbCoO3 was prepared using a water-soluble complex method at relatively low temperatures. Common chelating ligands such as citric acid were employed for the synthesis of complex-based precursors, followed by thermal decomposition of the precursors at high temperatures. X-ray diffraction data were collected and the crystal structure was refined by the Rietveld method. The structure of YbCoO3 can be described as a sesquioxide C-M2O3-like structure with space group Ia-3 and unit-cell parameter a=10.4470 (2). The Yb3+ and the Co3+ cations are found to preferentially occupy the two nonequivalent 8d and 24d sites, respectively. The two independent atoms Yb/Co have octahedral coordination; however, the degrees of distortion of their coordination polyhedron are different. The relationship between the title compound and the orthorhombic Perovskite structure of YbCoO3 reported in the literature is established.

The crystal structures of Mn, Zn, and Cd nitroprussides in their anhydrous state, M[Fe(CN)5NO] (M=Mn, Zn, Cd), were refined from XRD powder patterns using the Rietveld method. These compounds have a porous framework useful for adsorption and storage of small molecules. Water crystallization can be removed by heating below 100 °C without disrupting the 3D network by introducing certain structural modification mainly around the M site (Mn, Zn, Cd). For M=Mn and Cd, the compounds were found to be orthorhombic with space group Pnma [Mn:a=13.7844(1), b=7.3750(2), c=10.9470(2) Å, V=1112.8(1) Å3, Z=4; Cd:a=13.9566(3), b=7.5040(4), c=11.0230(2) Å, V=1154.4(1) Å3, Z=4]. Anhydrous zinc nitroprusside crystallizes in rhombohedral with space group R3 [a=b=19.2525(1), c=17.7107(2) Å, γ=120.0°, V=5685.1(1) Å3, Z=18]. When exposed to humid air, these anhydrous compounds become hydrated. The XRD powder patterns were recorded under vacuum on samples dehydrated in situ. The structural information from XRD was complemented with thermo-gravimetric, infrared, and Mössbauer data.

Synthesis and structure of two phosphates belonging to the ternary Sb2O5-Fe2O3-P2O5 system are reported. Structures of both SbV1.50FeIII0.50(PO4)3 and (SbV0.50FeIIIe0.50)P2O7 phases, obtained by solid state reaction in air atmosphere at 950 °C and 900 °C, respectively, were determined at room temperature from X-ray powder diffraction using the Rietveld method. Sb1.50Fe0.50(PO4)3 phosphate belongs to the Nasicon-type structure with R32 space group. Hexagonal cell parameters are ahex.=8.305(1) Å and chex.=22.035(2) Å. Rietveld refinement results show a 2-2 ordered distribution, along the c-axis, of X(1) and X(2) sites (crystallographic formula [Sb0.88Fe0.12]X(1)[Fe0.38Sb0.62]X(2)(PO4)3) in the Nasicon framework. (Sb0.50Fe0.50)P2O7 is isotypic with β-SbP2O7 pyrophosphate [Pna21 space group; a=7.865(1) Å, b=15.699(2) Å, c=7.847(1) Å]. Its crystal structure is built up from corner-shared SbO6 or FeO6 octahedra and P2O7 groups (two group types). Each P2O7 group shares its six vertices with three SbO6 and three FeO6 octahedra, and each octahedra is connected to six P2O7 groups. A quasi 1-1 ordered distribution, along the b-axis, of Sb5+ and Fe3+ ions in the pyrophosphate framework are observed.

X-ray powder diffraction data for the tetraphosphinic Si(CH2PPh2)4 silane are reported. Its crystal and molecular structures were determined by simulated annealing and full-profile Rietveld refinement methods. Si(CH2PPh2)4 was found to have tetragonal symmetry with P-421c space group. The lattice parameters were determined to be a=17.211(2) Å, c=7.553(1) Å, V=2237.5(5) Å3. The crystal structure was found to contain isolated Si(CH2PPh2)4 molecules. In each Si(CH2PPh2)4 molecule, the central Si atom was fixed at the −4 symmetric position bearing four CH2PPh2 branches. This environment was confirmed by 31P CP/MAS NMR measurements. Thermo-diffractometric measurements in the 20–120 °C range were also used to estimate the linear and volumetric thermal expansion coefficients (∂ ln V/∂T=1.8×10−4 K−1), typical for very “soft” materials.

Trigonal rare-earth dioxymonocyanamides Ln2O2CN2 (Ln=Dy, Ho, Er, Tm, Yb) were synthesized by the modified solid-state metathesis (SSM) method, in which Ln2O3 and melamine C3N6H6 were mixed and heated at 850 °C in vacuumed silica ampoules. Possible chemical reaction pathways are proposed. X-ray diffraction (XRD) patterns of Ln2O2CN2 were refined using the Rietveld method. Compounds Ln2O2CN2 crystallize in the trigonal system with space group P3m1, Z=1, and cell parameters of a and c varying from 3.7267(1) to 3.6407(1) Å and from 8.1848(3) to 8.1152(3) Å, respectively, as Ln atoms change from Dy to Yb. These compounds have stacking structures of Ln2O22+ and CN22− layers, similar to those of previously reported compounds Ln2O2CN2 (Ln=Ce, Pr, Nd, Sm, Eu, Gd). The presence of CN22− ions has been confirmed by infrared spectroscopy, with two characteristic peaks in the vicinity of 651 and 2075 cm−1.

In the course of an investigation of cracks in certain magnesia floors containing the mineral chlorartinite [Mg2(CO3)(H2O)(OH)]Cl·H2O, the dehydration process of chlorartinite was carried out in high vacuum. The crystal structure of dehydrated chlorartinite [Mg2(CO3)(H2O)(OH)]Cl was refined from laboratory X-ray powder diffraction data using the Rietveld method [R3c, a=22.6791(5) Å, c=7.22336(14) Å, V=3217.52(11) Å3, Z=18, Rp=4.13%, Rwp=5.82%]. Dehydrated chlorartinite exhibits the same type of 3D honeycomb zeolite-like crystal structure with large channels as the hydrated form. Compared to the hydrated form, the channels of dehydrated chlorartinite are empty because of the removal of all non-coordinating water molecules with the cell volume shrinking by 4.0%, leading to a more distorted environment of the magnesium atoms.

X-ray powder diffraction data collected for the complex silver(I) cyclamate [Ag(C6H12NO3S)] are reported. This material was obtained from a stoichiometric mixture of sodium cyclamate and AgNO3. The analysis of the data using the Le Bail method showed that the complex has monoclinic symmetry (space group C2/c). The unit cell parameters are a=31.85852(16) Å, b=6.25257(6) Å, c=8.46165(7) Å, and β=95.7651(5)°.

X-ray powder diffraction data and unit cells parameters for a monoclinic variety of the popular herbicide 2-chloro-N-(pyrazol-1-ylmethyl) acetyl-2′, 6′-xylidide, commonly known as metazachlor, butisan, and butichlor, is presented [a=7.306(3) Å, b=17.824(9) Å, c=10.728(3) Å, β=98.46(4)°, space group P21/c, cell volume=1381.82 Å3, Z=4]. The four strongest peaks (Irel>25) at 8.87, 7.19, 4.57, and 4.45 Å are quite distinctive, thus X-ray powder diffraction provides a quick, simple, and definitive method of identifying this form of material from other commercially available herbicide products.

We know a lot about normal values of bond distances, bond angles, torsion angles, and other molecular parameters. This knowledge can be incorporated into the structure solution process and into Rietveld refinement through the use of restraints and rigid bodies. An important measure of the quality of the refined model is the chemical reasonableness of molecular geometry. Refinement of the structures of calcium tartrate tetrahydrate and guaifenesin is used to illustrate the importance of chemical reasonableness in determining the quality of a Rietveld refinement.

A series of Internet-distributed audio/visual recordings for learning crystallographic analysis of powder diffraction data is discussed. These recordings provide a compact mechanism for distributing educational information. Such presentations provide hands-on discussion beyond what is usually presented in instructional texts. In some cases similar material can be presented with HTML text, but recordings can be created with significantly less effort and are superior for software demonstration.