First-Principles Hydrothermal Synthesis Design to Optimize Conditions and Increase the Yield of Quaternary Heteroanionic Oxychalcogenides
Lauren N. Walters, Chi Zhang, Vinayak P. Dravid, Kenneth R. Poeppelmeier, James M. Rondinelli
Abstract
Hydrothermal synthesis exploits solvent properties, temperature, and pressure to control reaction equilibrium among heterogeneous phases to promote the formation of targeted products, often single-anion-based ceramics (homoanionic materials). Heteroanionic materials with more than one anion present greater phase competition in the hydrothermal medium, making it more challenging to ascertain optimal processing variables. Here, we present a series of hydrothermal syntheses informed by first-principles thermodynamic models, which account for synthesis conditions (reagent concentration, pH, and temperature), and achieve four complex bismuth oxychalcogenides, BiMOQ (M = Cu, Ag; Q = S, Se) in high yield. Our computation-prior-to-experimentation procedure utilizes single-element and multi-element electrochemical (pH-potential) diagrams computed using density functional theory at (non)standard states. We construct stability diagrams to identify the optimal synthesis conditions for the formation of thermodynamically stable phases by requiring product yields of >90% on the stability diagrams. Furthermore, we calculate the most likely byproducts to occur in each system by analyzing reaction driving forces. Last, we synthesize the oxychalcogenides guided by these hydrothermal processing conditions and explain their yield successes based on materials-chemistry differences. Our work provides a strategy to understand, accelerate, and devise de novo hydrothermal syntheses of heteroanionic and chemically complex materials by design prior to experimentation.