Improved calibration of area detectors using multiple placements.

Calibration of area detectors from powder diffraction standards is widely used at synchrotron beamlines. From a single diffraction image, it is not possible to determine both the sample-to-detector distance and the wavelength, but, with images taken from multiple positions along the beam direction and where the relative displacement is known, the sample-to-detector distance and wavelength can both be determined with good precision. An example calibration using the GSAS-II software package is presented.

Rietveld in 100 picoseconds.

A recent article by Von Dreele, Clarke & Walsh [J. Appl. Cryst. (2021), 54, https://doi.org/10.1107/S1600576720014624] introduces an entirely new paradigm in structure determination, where a complete structural measurement is made in a tenth of a nanosecond.

Multiferroic behavior associated with an order-disorder hydrogen bonding transition in metal-organic frameworks (MOFs) with the perovskite ABX3 architecture.

Multiferroic behavior in perovskite-related metal-organic frameworks of general formula [(CH(3))(2)NH(2)]M(HCOO)(3), where M = Mn, Fe, Co, and Ni, is reported. All four compounds exhibit paraelectric-antiferroelectric phase transition behavior in the temperature range 160-185 K (Mn: 185 K, Fe: 160 K; Co: 165 K; Ni: 180 K); this is associated with an order-disorder transition involving the hydrogen bonded dimethylammonium cations. On further cooling, the compounds become canted weak ferromagnets below 40 K. This research opens up a new class of multiferroics in which the electrical ordering is achieved by means of hydrogen bonding.

Order-disorder antiferroelectric phase transition in a hybrid inorganic-organic framework with the perovskite architecture.

[(CH3)2NH2]Zn(HCOO)3, 1, adopts a structure that is analogous to that of a traditional perovskite, ABX3, with A = [(CH3)2NH2], B = Zn, and X = HCOO. The hydrogen atoms of the dimethyl ammonium cation, which hydrogen bond to oxygen atoms of the formate framework, are disordered at room temperature. X-ray powder diffraction, dielectric constant, and specific heat data show that 1 undergoes an order-disorder phase transition on cooling below 156 K. We present evidence that this is a classical paraelectric to antiferroelectric phase transition that is driven by ordering of the hydrogen atoms. This sort of electrical ordering associated with order-disorder phase transition is unprecedented in hybrid frameworks and opens up an exciting new direction in rational synthetic strategies to create extended hybrid networks for applications in ferroic-related fields.

Propene adsorption sites in zeolite ITQ-12: a combined synchrotron X-ray and neutron diffraction study.

The adsorption site of propene in the small-pore, pure silica zeolite [Si24O48]-ITW-ITQ-12 has been characterized via Rietveld refinement of the crystal structure of propene-loaded ITQ-12 on the basis of synchrotron X-ray and neutron diffraction data taken at 298 K. The structure can be described with a monoclinic unit cell having Cm symmetry and unit cell parameters a = 10.436 angstroms, b = 15.018 angstroms, c = 8.855 angstroms, beta = 105.74 degrees, and volume = 1335.9 angstroms3. Four-fold disordered adsorption sites that are nearly equivalent relative to the cage's 2/m pseudosymmetry are located near the center of each ellipsoidally shaped [4(4)5(4)6(4)8(4)] cage. At this site, the adsorbed propene molecule lies on a plane close and approximately parallel to the equatorial plane of the cage and is aligned with its methylene group pointing toward the pore's eight-ring window. The refined propene concentration, 1.8 per unit cell content, is close to one propene molecule per [4(4)5(4)6(4)8(4)] cage and the amount observed in adsorption experiments at 298 K and 1 atm propene partial pressure.

Determination of standard uncertainties in fits to pair distribution functions.

Methods are developed to establish the limits of statistical uncertainty for values computed from a pair distribution function (PDF) or models fit to a PDF. This is done by computation of a variance-covariance matrix for the PDF from the uncertainties in the diffraction intensities. The application of this variance-covariance matrix also offers optimal weighting for least-squares refinement.

A dedicated powder diffraction beamline at the advanced photon source: commissioning and early operational results.

A new dedicated high-resolution high-throughput powder diffraction beamline has been built, fully commissioned, and opened to general users at the Advanced Photon Source. The optical design and commissioning results are presented. Beamline performance was examined using a mixture of the NIST Si and Al(2)O(3) standard reference materials, as well as the LaB6 line-shape standard. Instrumental resolution as high as 1.7 x 10(-4) (DeltaQQ) was observed.

A twelve-analyzer detector system for high-resolution powder diffraction.

A dedicated high-resolution high-throughput X-ray powder diffraction beamline has been constructed at the Advanced Photon Source (APS). In order to achieve the goals of both high resolution and high throughput in a powder instrument, a multi-analyzer detector system is required. The design and performance of the 12-analyzer detector system installed on the powder diffractometer at the 11-BM beamline of APS are presented.

Role of the hydroxyl-water hydrogen-bond network in structural transitions and selectivity toward cesium in Cs0.38(D1.08H0.54)SiTi2O7.(D0.86H0.14)2O crystalline silicotitanate.

The crystal structure of the selective Cs+ ion exchanger D1.6H0.4Ti2SiO7.D2.66H0.34O1.5, known as crystalline silicotitanate or CST, has been determined in both native (D-CST) and in the Cs+-exchanged forms ((Cs, D)-CST) from angle-dispersive and time-of-flight neutron diffraction studies. The final fully exchange Cs+ form transformed from D-CST with unit cell parameters a = 11.0704(3) A c = 11.8917(5) A and space group P42/mbc, to one with a = 7.8902(1) A c = 11.9051(4) A and space group P42/mcm. Rietveld structure refinements of both D-CST and (Cs, D)-CST suggest the transition, and ultimately the selectivity, is driven by changes in the positions of water molecules, in response to the initial introduction of Cs+. The changes in water position appear to disrupt the D-O-O-D dihedral associated with the CST framework in space group P42/mbc which ultimately leads to the structural transition. The new geometric arrangement of the water-deuteroxyl network in (Cs, D)-CST suggests that Dwater-Ddeuteroxyl repulsion forced by Cs+ exchange drives the structural transformation.

The indium subnitrides Ae6In4(InxLiy)N(3-z)(Ae = Sr and Ba).

The indium nitrides Sr6In4(In(0.32)Li(0.92))N(2.49) and Ba6In(4.78)N(2.72) have been synthesized from an excess of molten sodium. They crystallize in a stuffed variant of the eta-carbide structure type in the cubic space group Fdm with Z = 8. The lattice parameters are a = 14.3752(4) and 15.216(1) A, with cell volumes 2970.6(2) and 3523.3(6) A3, respectively. In both compounds there are vacancies on some of the indium and nitrogen sites and, in the case of Sr6In4(In(0.32)Li(0.92))N(2.49), mixed lithium-indium occupancy of one metal site. It is demonstrated that the partial and mixed occupancies act to carefully tune to electron count to almost fulfill the bonding requirements of the stellar quadrangular subnets of both compounds. Four probe resistivity measurements performed upon a pellet of Sr6In4(In(0.32)Li(0.92))N(2.49) show it to have a room-temperature resistivity of 6.3 mOmega.cm with a weak temperature dependence.