Mechanism and microstructures in Ga2O3 pseudomartensitic solid phase transition.

Understanding solid-to-solid phase transitions remains a challenge in materials science. While these transformations are widely used in material synthesis, predicting their kinetics and resulting microstructures is complex. The Ga2O3 α-β phase transformation is a well-known example, but its atomistic mechanism was previously unknown. Earlier studies suggested that synthetic conditions influence whether the product is amorphous or crystalline, but the underlying reasons were unclear. This gap motivated researchers to explore the transformation's atomic-level behavior. Prior research has shown that phase transitions involve various mechanisms, such as martensitic shearing or reconstructive diffusion. However, no prior work had resolved the detailed steps of Ga2O3 α-β transformation. This uncertainty drove the development of new computational methods to study the process. The field lacks a unified framework for predicting crystallinity outcomes. This paper aims to address that gap.

This study aimed to determine the atomistic mechanism of the Ga2O3 α-β phase transformation. The transformation involves changes in cation coordination and crystal density, making it a complex system to model. The researchers sought to understand how the reaction pathway influences the crystallinity of the product. They focused on the Ga2O3 system because it is a common but poorly understood phase transition. The goal was to resolve the reaction pathway using computational methods. The study aimed to identify the factors that determine whether the product is amorphous or crystalline. By resolving the atomistic steps, the researchers hoped to propose general rules for predicting crystallinity outcomes. The work also aimed to distinguish this transformation from other known phase transition types.

The researchers employed the stochastic surface walking (SSW) method to model the Ga2O3 α-β phase transformation. This approach allows for the exploration of complex reaction pathways by simulating atomic movements. The method was used to identify the sequence of steps in the transformation. The study combined computational modeling with experimental validation. High-resolution transmission electron microscopy (HRTEM) was used to observe the atomic structure of the transition. The researchers analyzed the formation of biphase junctions and lattice expansion in the β phase. The model predicted the involvement of multiple types of phase transition steps. The method enabled the identification of rate-determining steps and intermediate phases. The computational results were compared with experimental observations to confirm the model's accuracy.

The study revealed a multi-step, multi-type reaction pathway for the Ga2O3 α-β phase transformation. The process involves seven intermediate phases and includes shearing of O layers, Ga atom diffusion, and lattice dilation. The Ga atom migration across O layers is the rate-determining step, leading to amorphous-like intermediates. The shearing of O layers contributes to the formation of coherent biphase junctions. The study identified a crystallographic orientation relation: (001)α//(201̄)β + [120]α//[13̄2]β. HRTEM confirmed the atomic structure of the biphase junction and the formation of (201̄)β twins. The β phase shows lattice expansion after nucleation from the α phase. The results demonstrate that the transformation is a new type of diffusionless phase transition, termed pseudomartensitic.

The study provides the first atomistic mechanism for the Ga2O3 α-β phase transformation. The transformation involves a unique combination of shearing, diffusion, and dilation steps. The researchers propose that the sensitivity of product crystallinity is due to the multi-step nature of the pathway. The findings distinguish pseudomartensitic transitions from other types of phase transformations. The study confirms the presence of coherent biphase junctions and orientation relations. HRTEM observations support the computational predictions. The results offer general rules for predicting crystallinity outcomes in solid phase transitions. The new knowledge complements existing theories of diffusionless phase transitions.