@article{weng_dill_martin_whitfield_hoffmann_ye_2020, title={K-space algorithmic reconstruction (KAREN): a robust statistical methodology to separate Bragg and diffuse scattering}, volume={53}, ISSN={1600-5767}, url={http://dx.doi.org/10.1107/S1600576719017060}, DOI={10.1107/S1600576719017060}, abstractNote={Diffuse scattering occurring in the Bragg diffraction pattern of a long-range-ordered structure represents local deviation from the governing regular lattice. However, interpreting the real-space structure from the diffraction pattern presents a significant challenge because of the dramatic difference in intensity between the Bragg and diffuse components of the total scattering function. In contrast to the sharp Bragg diffraction, the diffuse signal has generally been considered to be a weak expansive or continuous background signal. Herein, using 1D and 2D models, it is demonstrated that diffuse scattering in fact consists of a complex array of high-frequency features that must not be averaged into a low-frequency background signal. To evaluate the actual diffuse scattering effectively, an algorithm has been developed that uses robust statistics and traditional signal processing techniques to identify Bragg peaks as signal outliers which can be removed from the overall scattering data and then replaced by statistically valid fill values. This method, described as a `K-space algorithmic reconstruction' (KAREN), can identify Bragg reflections independent of prior knowledge of a system's unit cell. KAREN does not alter any data other than that in the immediate vicinity of the Bragg reflections, and reconstructs the diffuse component surrounding the Bragg peaks without introducing discontinuities which induce Fourier ripples or artifacts from underfilling `punched' voids. The KAREN algorithm for reconstructing diffuse scattering provides demonstrably better resolution than can be obtained from previously described punch-and-fill methods. The superior structural resolution obtained using the KAREN method is demonstrated by evaluating the complex ordered diffuse scattering observed from the neutron diffraction of a single plastic crystal of CBr4 using pair distribution function analysis.}, number={1}, journal={Journal of Applied Crystallography}, publisher={International Union of Crystallography (IUCr)}, author={Weng, James and Dill, Eric D. and Martin, James D. and Whitfield, Ross and Hoffmann, Christina and Ye, Feng}, year={2020}, month={Feb}, pages={159–169} }
@article{hillis_losey_weng_ghaleb_hou_martin_2017, title={From rate measurements to mechanistic data for condensed matter reactions: a case study using the crystallization of [Zn(OH2)(6)][ZnCl4]}, volume={7}, ISSN={2073-4352}, url={http://dx.doi.org/10.3390/cryst7010011}, DOI={10.3390/cryst7010011}, abstractNote={The kinetics of crystallization of the R = 3 hydrate of zinc chloride, [Zn(OH2)6][ZnCl4], is measured by time-resolved synchrotron x-ray diffraction, time-resolved neutron diffraction, and by differential scanning calorimetry. It is shown that analysis of the rate data using the classic Kolmogorov, Johnson, Mehl, Avrami (KJMA) kinetic model affords radically different rate constants for equivalent reaction conditions. Reintroducing the amount of sample measured by each method into the kinetic model, using our recently developed modified-KJMA model (M-KJMA), it is shown that each of these diverse rate measurement techniques can give the intrinsic, material specific rate constant, the velocity of the phase boundary, vpb. These data are then compared to the velocity of the crystallization front directly measured optically. The time-resolved diffraction methods uniquely monitor the loss of the liquid reactant and formation of the crystalline product demonstrating that the crystallization of this hydrate phase proceeds through no intermediate phases. The temperature dependent vpb data are then well fit to transition zone theory to extract activation parameters. These demonstrate that the rate-limiting component to this crystallization reaction is the ordering of the waters (or protons) of hydration into restricted positions of the crystalline lattice resulting in large negative entropy of activation.}, number={1}, journal={Crystals}, publisher={MDPI AG}, author={Hillis, B. G. and Losey, B. P. and Weng, J. and Ghaleb, N. and Hou, F. and Martin, J. D.}, year={2017}, pages={11} }