Conversely, advances in sources and instrumentation at many synchrotron and neutron scattering centres, including large and sensitive detectors, are increasingly facilitating cutting-edge operando powder diffraction experiments. In-house laboratory X-ray diffractometers can be customized and dedicated to a particular type of experiment, offering an advantage over diffractometers at large-scale synchrotron and neutron radiation facilities which are shared internationally and tend to be multipurpose. (ii) Tuning instrumental optics in order to trade some angular resolution for increased flux (resolution/intensity), thereby decreasing data acquisition time.įunctional materials analysis is greatly enhanced by modern high-speed instrumentation, which allows the rapid collection of high-quality data and real-time information concerning the functioning/responding material. (i) Reducing the rate of change of the material response, such as by reducing the system temperature in order to influence the reaction kinetics. Several strategies can be taken to keep the distribution of states small in any particular measurement, including: The level of detail gained about the material structure is in direct competition with the level of detail gained concerning its evolution. Operando diffraction experiments are therefore relatively demanding, as they often require the sample of interest to be probed within a device and with sufficiently fast acquisition times to represent the process being measured. Because all powder diffraction data represent a time-averaged measurement, the distribution of states that are represented in the sample during the period of data acquisition must be taken into account, complicating the structural analysis. Ideally, studies of functional host–guest systems should probe guest transport mechanisms during function within a device or during the material's response to external stimuli ( operando studies), to avoid obtaining misleading or incomplete results from the equilibrium system. Such in situ studies of the system at equilibrium are increasingly being recognized as not representative of the structural processes occurring during real-time function, and there are examples, notably in battery electrodes, where this assumption is demonstrably incorrect (Grey & Tarascon, 2017 ). are widely conducted on such systems, but the vast majority of these involve measurements of the system only at equilibrium at discrete points in the parameter space, with the assumption that the system's response to the external stimulus is correctly represented. In situ diffraction experiments under variable conditions of guest concentration, temperature, charge rate etc. Whilst studies of non-equilibrium systems using powder diffraction are commonplace, and include crystallization (Simmance et al., 2015 ) and other reactions (Hansen & Kohlmann, 2014 ), the use of the method to study guest–host systems is less common. Time-resolved powder diffraction is an established tool for the investigation of processes and kinetics (Eckold et al., 2010 Evans & Evans, 2004 Leineweber & Mittemeijer, 2012 Norby, 1996 ). How the charge or energy carrier (molecule) enters, moves through and is stored within the host, as well as the corresponding reverse processes that release the charge or energy carrier, all need to be understood. These materials must often reversibly host charge or energy carriers, and characterizations focused on understanding how these guests are accommodated by the host material are central to technological advancement. Their atomic structure influences their chemical and physical properties, which in turn underpin the performance characteristics of energy devices. Functional energy materials form the central part of many important technologies used for the storage, transport and delivery of energy.
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