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In the recently developed technique of X-ray Birefringence Imaging, molecular orientational order in anisotropic materials is studied by exploiting the birefringence of linearly polarized X-rays with energy close to an absorption edge of an element in the material. In the experimental setup, a vertically deflecting high-resolution double-crystal monochromator is used upstream from the sample to select the appropriate photon energy, and a horizontally deflecting X-ray polarization analyzer, consisting of a perfect single crystal with a Bragg reflection at Bragg angle of approximately 45°, is placed downstream from the sample to measure the resulting rotation of the X-ray polarization. However, if the experiment is performed on a synchrotron bending-magnet beamline, then the elliptical polarization of the X-rays out of the electron orbit plane affects the shape of the output beam. Also, because the monochromator introduces a correlation between vertical position and photon energy to the X-ray beam, the polarization analyzer does not select the entire beam, but instead selects a diagonal stripe, the slope of which depends on the Bragg angles of the monochromator and the polarization analyzer. In the present work, the final background intensity distribution is calculated analytically because the phase space sampling methods normally used in ray traces are too inefficient for this setup. X-ray Birefringence Imaging data measured at the Diamond Light Source beamline B16 agree well with the theory developed here. [ABSTRACT FROM AUTHOR]

Among homologous series of metal oxides, Andersson‐Magnéli phases TinO2n‐1 (n=4–10) have attracted renewed scientific attention because of their behaviour in electrical conductivity and chemical/thermal stability. Various applications have also been reported for the phases with different values of n, or slightly reduced rutile (TiO2). The characteristic properties of these materials depend strongly on the compositional deviation from TiO2 and the way in which the structure accommodates the deviation. Thus, an urgent requirement is to overcome difficulties in characterizing such materials at atomic resolution. Here, we trace the discovery of the Andersson‐Magnéli phases, and report the application of recent developments in electron microscopy to reveal the relation, at the local level, between structural characteristics and electronic states, specifically for the materials TinO2n‐1 with n=4–8. The electrical conductivity of Ti4O7 has been reported previously to show three clearly distinct states on decreasing temperature from 300 K. For this reason, we focus on Ti4O7 as a representative example of the TinO2n‐1 phases and report structural characteristics at temperatures corresponding to each of the three different phases, focusing on the distribution of Ti3+ and Ti4+ cations from analysis of single‐crystal XRD data. Electron diffraction experiments and electrical conductivity measurements are also reported. [ABSTRACT FROM AUTHOR]

We consider those crystalline inclusion compounds that can be modeled as one-dimensional systems, and develop a mathematical model in which the one-dimensional inclusion compound comprises a linear, infinite host channel (with periodic repeat distance ch along the channel axis) containing a regular, periodic arrangement of n guest molecules (with periodic repeat distance cg ). The principal aim of this paper is to develop a method for the quantitative prediction of cg, and a theoretically justified procedure is described for using known potential energy functions for host–guest and guest–guest interactions as a route towards deriving this information. Fundamental to the analysis is the definition of an appropriate energy expression—denoted the ‘‘characteristic energy’’ of an inclusion compound E(α,n)—that directly indicates the relative energetic favorability of inclusion compounds with different guest periodicities α(α=cg/ch). Then, via a graphical method—the characteristic energy diagram, which is essentially a means of constructing a bounded region that will contain the points (α,E(α,n))—a restricted range containing the optimal value of α can be determined. A procedure is provided for constructing the characteristic energy diagram using computed potential energy functions for ‘‘real’’ inclusion compounds, and the method for interpretation of the diagram is discussed in full.Furthermore, our method of analysis not only permits an assessment of the optimum guest periodicity for the inclusion compound, but also addresses, from energetic considerations, the question of whether ‘‘lock-in’’ of the host and guest substructures will occur. The applicability of our method of analysis is illustrated using potential energy functions computed for the hexadecane/urea inclusion compound. The characteristic energy... [ABSTRACT FROM AUTHOR]

A polycrystalline sample of pure benzene-1,2,3-triboxylic acid (BTCA) was obtained by dehydration of BTCA dihydrate at elevated temperature. Power X-ray diffraction (PXRD) confirmed that this process leads to a new solid phase with no detectable amount of BTCA dihydrate remaining and high solution solid-state C NMR was consistent wit the assignment of the new phase as pure BTCA.

Solid-state NMR spectroscopy is a well-established and versatile technique for studying the structural and dynamic properties of solids, and there is considerable potential to exploit the power and versatility of solid-state NMR for in-situ studies of chemical processes. However, a number of technical challenges are associated with adapting this technique for in-situ studies, depending on the process of interest. Recently, an in-situ solid-state NMR strategy for monitoring the evolution of crystallization processes has been developed and has proven to be a promising approach for identifying the sequence of distinct solid forms present as a function of time during crystallization from solution, and for the discovery of new polymorphs. The latest development of this technique, called `CLASSIC' NMR, allows the simultaneous measurement of both liquid-state and solid-state NMR spectra as a function of time, thus yielding complementary information on the evolution of both the liquid phase and the solid phase during crystallization from solution. This article gives an overview of the range of NMR strategies that are currently available for in-situ studies of crystallization processes, with examples of applications that highlight the potential of these strategies to deepen our understanding of crystallization phenomena. [ABSTRACT FROM AUTHOR]