Selective formation of metastable polymorphs in solid-state synthesis

TL;DR

This paper introduces a theoretical framework to predict and control the formation of metastable polymorphs in solid-state synthesis, emphasizing reaction energy and precursor effects to enable targeted material design.

Contribution

It presents a novel approach using reaction energy and precursor selection to control polymorph formation in solid-state reactions, supported by in situ characterization and DFT calculations.

Findings

Reaction energy influences polymorph nucleation.

Precursor choice can direct metastable phase formation.

Framework predicts conditions for metastable polymorph synthesis.

Abstract

Metastable polymorphs often result from the interplay between thermodynamics and kinetics. Despite advances in predictive synthesis for solution-based techniques, there remains a lack of methods to design solid-state reactions targeting metastable materials. Here, we introduce a theoretical framework to predict and control polymorph selectivity in solid-state reactions. This framework presents reaction energy as a rarely used handle for polymorph selection, which influences the role of surface energy in promoting the nucleation of metastable phases. Through in situ characterization and density functional theory calculations on two distinct synthesis pathways targeting LiTiOPO4, we demonstrate how precursor selection and its effect on reaction energy can effectively be used to control which polymorph is obtained from solid-state synthesis. A general approach is outlined to quantify the conditions under which metastable polymorphs are experimentally accessible. With comparison to historical data, this approach suggests that using appropriate precursors could enable the synthesis of many novel materials through selective polymorph nucleation.