In situ synchrotron X-ray powder diffraction can be one of the most powerful probes to investigate the structure evolution by a chemical reaction thanks to simultaneity of data collection. It is not, however, with ease to produce a homogeneous chemical reaction in the limited spaces, which is essential to see an atomic-scale structure evolution. We have developed an in situ capillary cell for both high-temperature H2reduction and precise humidity control at the SPring-8 BL44B2. We successfully applied this in situ system to an electronic conductor LaSr3Fe3O10, which is transformed into an ionic conductor by the two-step chemical treatments [1]. LaSr3Fe3O10has a triple-layer structure with a FeO6octahedral unit. One triple layer is bonded with another layer through van der Waals interaction. Structure refinements with in situ synchrotron powder diffraction data revealed that the H2reduction at 613 K produced in-plane oxygen vacancies, which resulted in suppression of the interlayer interaction. We found from charge density studies and Raman spectroscopy measurements that the following humidification intercalated H2O and OH-into the interlayer and intralayer, respectively. That means that H2O plays a role for suppression of three-dimensional electronic conductivity, stabilizing the intercalation structure. On the other hand, the OH-ions behave as carriers for ionic conductivity, maintaining the charge neutrality in the intralayer. Finally we determined the composition of the ionic conductor to be LaSr3Fe3O8.0(OH)1.2·2H2O, which indicates a transformation of LaSr3Fe3O10into an OH-ionic conductor. In the presentation, I will discuss the OH-ionic conduction channel based on electrostatic potentials obtained from charge densities.
In-situ early-age hydration study of sulfobelite cements by synchrotron powder diffraction
