Newswise —
In order to design new material compounds in a logical manner, comprehending the mechanisms that underlie their synthesis is crucial. Commonly used analytical methods, such as nuclear magnetic resonance and spectroscopy, are applied to investigate these mechanisms in molecular reactions. However, the reaction pathways that govern the formation of solid-state crystalline compounds are not yet well understood. This is primarily because of the irregular reactions and extreme temperatures that occur in solid-state compounds. Additionally, the intricate nature of solid crystalline compounds, which contain numerous atoms, impedes accurate analysis. Therefore, it is imperative to develop new techniques that can overcome these obstacles.
In recent times, the use of in-situ synchrotron X-ray diffraction (XRD) techniques has gained momentum in the study of reactions taking place in crystalline phases. Due to their rapidity and temporal resolution, synchrotron XRD methods enable the acquisition of reaction data within very brief time intervals (a few hundred milliseconds). Consequently, this technique exhibits potential in capturing data related to transient intermediate reaction phases.
A team of Japanese scientists has utilized a cutting-edge synchrotron X-ray diffraction technique to document the topochemical solid-gas reduction mechanisms occurring in layered perovskite. The research, which was published in the journal Advanced Science, was spearheaded by Associate Professor Takafumi Yamamoto from Tokyo Institute of Technology (Tokyo Tech).
Dr. Yamamoto elaborates, "We selected Sr3Fe2O7-δ, which belongs to the Ruddlesden-Popper type of layered perovskite, due to its remarkable oxygen storage capacity. Sr3Fe2O7-δ exhibits rapid and reversible topochemical redox reactions when subjected to O2 and H2, and demonstrates exceptional environmental catalytic performance as a result."
Previous findings by Dr. Yamamoto's colleagues had revealed that doping Sr3Fe2O7-δ with Palladium (Pd) considerably amplifies the rate of oxygen release while lowering the temperature at which the release occurs. Building upon these findings, the team conducted a study to investigate the structural evolution and reaction pathways of this perovskite during the solid-gas reduction process.
To begin the study, the team created two samples: a pristine sample and a Pd-doped sample of Sr3Fe2O7-δ. They then employed high-speed synchrotron X-ray diffraction to track the samples as they underwent rapid oxygen deintercalation (reduction).
Through the analyses, the team discovered that the reduction of the pristine Sr3Fe2O7-δ sample took place through thermodynamically stable phases. This sample underwent a gradual, single-phase structural transformation throughout the reduction process. Conversely, the reduction of the Pd-doped Sr3Fe2O7-δ sample followed a distinctly different pathway, involving intermediate phases that were not in equilibrium. Initially, this sample transformed into a dynamically disordered phase for a few seconds before reorganizing itself through a first-order transition to achieve the final ordered and stable state.
Moreover, the team found that Pd metal particles present on the surface of Sr3Fe2O7-δ considerably hastened the oxygen deintercalation reaction of Pd-doped Sr3Fe2O7-δ as compared to the pristine sample. Dr. Yamamoto comments, "The transformation in reaction dynamics resulting from the Pd loading of Sr3Fe2O7-δ highlights the potential of surface treatment in manipulating the reaction mechanisms of a crystalline material."
In conclusion, the study's results demonstrate the potential of synchrotron XRD technique for analyzing reaction pathways in solid-state compounds and identifying their rate-determining steps. Such insight could aid in the rational design of high-performance functional materials by enabling the optimization of reaction pathways.
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