Diffractometer for time-resolved in-situ high temperature powder diffraction and X-ray reflectivity

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The research questions of the Institute of Crystallography (IfK) of RWTH Aachen University include temperature-dependent structural phase transformations, solid-state reactions (e.g. dewatering reactions, segregation), temperature-dependent redox reactions and sintering processes in (mostly ceramic) functional materials. To understand the underlying structural processes and their kinetics at the atomic level, many temperature-dependent and time-resolved data sets have to be collected, analyzed and compared. In addition, we study interfacial structures and processes between solids and liquids or gases. Modern X-ray diffractometers allow the methods of powder X-ray diffraction (PXRD) and X-ray reflectivity (XRR) to be combined in one device. Examinations with copper radiation usually deliver high intensities due to the high flux and therefore allow short measurement times on flat specimens in reflection. While the large wavelength enables a high angular resolution and thus a good reflection resolution on the one hand, it is not suitable for transmission measurements in capillaries even for medium-heavy elements due to the relatively strong absorption. Here, the use of shorter-wavelength (and therefore less strongly absorbed) Mo radiation is recommended. Especially, when measurements can be performed using a Kα1,2 wavelength mixture, this X-ray source also delivers considerable flux and thus good intensities with reasonable measurement times. For XRR or polycrystalline XRD samples without a defined, smooth surface (e.g. ceramic or metallic workpieces and components), primary Goebel mirrors are required for both X-ray sources. As a result, a parallel beam geometry is obtained for Cu. A focusing Göbel mirror is provided for the Mo tube for capillary measurements in transmission in order to obtain sufficiently high intensities with a small sample volume. This also allows XRR measurements and measurements under grazing incidence. A high-temperature chamber up to 1200 °C, which can be operated with both Cu and Mo radiation, under air, vacuum and inert gas with both flat samples (in reflection) and capillaries (in transmission), is a prerequisite for the successful research work of the IfK. XRR measurements require fine, motorized adjustment of the sample position (x, y, z) and tilt for optimal measurement conditions. The reflectometry method has already been optimized in the past for measuring liquid films, also on synchrotron beamlines, which requires vibration damping and/or decoupling of the sample from the environment. For fast (a few minutes), position-sensitive measurements, a 2D detector is required on the secondary side, which is suitable for XRR as well as time-resolved high-temperature diffraction with Cu and Mo radiation.