Development of Methods for Studying Ion Conductors
One of the main goals was to develop and adapt methods to study plastic crystals. Three approaches were initially considered: advanced diffraction techniques (which use X-rays or neutrons to map out atomic structures), nuclear magnetic resonance (NMR, which reveals how atoms move), and computer simulations using density functional theory (DFT). While each method provided useful insights, the most successful and practical approach turned out to be molecular dynamics (MD) simulations, which are computer models that track how atoms and molecules move over time.
Through these simulations, we were able to:
• Study how certain molecules (with a tetrahedral shape) inside the materials orient themselves.
• Measure how fast these molecules rotate and how quickly the ions move through the material, which is crucial for understanding their ability to conduct electricity.
These simulations were repeated at different temperatures, allowing us to create a reliable method for investigating both the structure and movement of ions in these materials. While we also tried using diffraction and NMR techniques, these methods were less consistent, so the project focused on MD simulations, which are more versatile and provide robust results.
Main achievement: We developed a reliable, computer-based method for studying plastic crystalline electrolytes, a class of materials that could play a key role in future energy storage technologies.
Understanding the Behavior of Plastic Crystal Materials
Using the methods developed, we studied three key materials: Na3PS4, Na3PO4, and Li2SO4. These materials were chosen because they share similar chemical structures, making them good candidates for comparison. The goal was to understand their internal structures and how their ions move, which is essential for improving their performance as conductors.
Through the simulations, we discovered:
• The molecules inside these materials don’t move randomly, as previously thought. Instead, they have specific orientations, which are different for each material.
• The speed at which these molecules rotate, and the speed at which the ions move, changes depending on the material’s chemical makeup.
• Surprisingly, there was no simple connection between the movement of the ions and the rotation of the molecules. This was unexpected, as earlier theories suggested there would be a direct link between the two.
These findings showed that each material behaves differently, and understanding these differences is key to unlocking their full potential as ion conductors. It also highlighted that there’s more complexity in the way these materials work than previously believed.
Main achievement: We gained new insights into how these materials work on a molecular level, discovering that their internal dynamics are more complex than expected, which opens the door for further research to optimize their performance.
