Lowering Ternary Oxide Synthesis Temperatures by Solid-State Cometathesis Reactions

Abstract

Low temperature synthesis routes are necessary for selectively synthesizing many metastable solid state materials. Here we identify a cooperative effect that starting materials have in lowering temperatures in solid state metathesis reactions by studying the formation of yttrium manganese oxide. Previous studies have shown that YMnO 3 can be synthesized by ternary metathesis with an alkali halide being produced as a secondary product. In this contribution, we show that by using alkaline earth metals instead of alkali metals, the polymorph selectivity of the reaction is changed, as orthorhombic YMnO 3 forms at lower temperatures than the hexagonal polymorph. Reactions were studied using ex post facto synchrotron X-ray diffraction. These experiments reveal that reactions using alkaline earth manganese oxides as a starting material require high temperatures to progress. Reaction temperatures can be lowered from 700 °C to 550 °C while maintaining phase selectivity by reacting both MgMn 2 O 4 and CaMn 2 O 4 with YOCl in a cooperative "cometathesis" reaction. The nascent halide salts appear to improve the reaction kinetics. Since the onset temperature for YMnO 3 formation falls 50 °C below the MgCl 2 -CaCl 2 liquidus, the enhanced reactivity is consistent with surface melting of a nasscent salt biproduct at the interfaces. Cometathesis routes have similar phase selectivity and temperature reduction in reactions that form TbMnO 3 , ErMnO 3 , and DyMnO 3 .Cometathesis lowers reaction temperatures while preserving reaction selectivity of the end members, making it a valuable approach for synthesizing metastable targets.

Machine-learning rationalization and prediction of solid-state synthesis conditions

“…The features used in this work to account for reaction thermodynamics were inspired by recent efforts to understand phase evolution during synthesis. [7][8][9]12,37 These features involve decomposing overall synthesis reactions into a sequence of phase evolution reactions between pairs of compounds and quantifying the grand potential thermodynamic driving force for these phase evolution reactions. This approach has been proved especially useful for understanding shown to provide little predictive power of synthesis conditions and even cause the models to generalize poorly on OOS datasets (as demonstrated in Fig.…”

“…[8][9][10][11] To design synthesis routes for new materials, it is essential to understand why certain conditions are preferred and develop models for predicting these conditions for synthesis (e.g., temperature, time). While thermodynamic calculations have been used to rationalize synthesis conditions in specific chemical systems, 8,12 a synthesis condition predictor with broad applicability for general inorganic compounds is still elusive.…”

nmfMapping: a cloud-based web application for non-negative matrix factorization of powder diffraction and pair distribution function datasets

“…The data were integrated using GSAS-II (Toby & Von Dreele, 2013) before being passed to the nmfMapping@PDFitc app. For more details of the experimental setup, see Wustrow et al (2021).…”

Predictive Synthesis

“…Many great chemists (just to name a few: Myung-Hwan Whangbo, Roald Hoffmann, Jeremy Burdett, and Linus Pauling) contributed to make theoretical and computational analysis a useful tool in understanding and predicting trends in crystal structure and properties of solid state compounds. ,− Recent advances in computer speed and algorithms make possible numerous predictions of crystal structures which in some cases were experimentally verified. With the encouragement of funding agencies, there are multiple examples of successful computational–-experimental collaborations, − but in the author’s opinion, the integration of computational and experimental communities still needs to be improved. When experimental or computational groups work separately from each other, they often may not recognize the limitations and interests of the other party and prefer to stay inside their comfort zone, i.e., predict or synthesize compounds they are good in predicting or synthesizing.…”