Role of evolving template on the transformation kinetics and microstructure of a product‐phase entropy‐stabilized oxide

Abstract We investigate the role of CoTiO 3 ‐TiO 2 template geometry on the microstructural evolution and growth kinetics associated with the formation of a product phase, CoTi 2 O 5 , in this reaction–diffusion system. For this purpose, the CoTi 2 O 5 transformation pathways for three templates having distinct reactant‐phase grain sizes were compared and contrasted using X‐ray diffraction, scanning electron microscopy, electron backscatter diffraction, and atomic force microscopy, and described by Johnson and Mehl, Avrami, and Kolmogorov kinetic analyses. Measurement of the relative magnitude of diphasic (CoTiO 3 ‐TiO 2 ) boundary energies was carried out via thermal grooving experiments. These analyses indicated that interphase boundary energy and template geometry dictate product‐phase nucleation and microstructural evolution in dramatic fashion. The stark differences in the nucleation behavior were consistent with classical nucleation theory and the significant difference in the diphasic boundary energies of template structures with differing duplex grain size. These findings offer a new perspective for understanding the relationship between initial reactant structure and final product microstructure, highlighting the role of template parameters as effective kinetic “knobs” that may be adjusted to create a desired product microstructure. Importantly, this capability to tune product‐phase morphology and transformation kinetics via templating opens new avenues for controlled microstructural design in advanced ceramic systems.