Chen Longqing's research established the first grain growth model based on phase field method. Using this model, Qin Long Chen and his collaborators studied the dynamics and topological structure of grain growth. Based on computer simulation, they show that the correlation of grain growth is the key factor, thus revealing the long-standing defects in the analysis of grain growth model. Many other research groups now use this model to study the grain growth kinetics in various systems. Chen Longqing's research group also extended their model to multiphase system, for example, using a unified model to study grain growth and Oswald ripening. Using the multiphase grain growth model, they can systematically study the Oswald ripening process in a two-phase system with a high percentage of mature stages for the first time in the world. This has become the basis of two projects, the World Materials Network Project and the Computational Materials Design Center, which are funded by the National Natural Science Foundation of the United States. Chen Longqing's research group is also a pioneer in phase field simulation of ferroelectric domains in single crystal materials and thin films with substrate constraints. They can be used to quantitatively predict the dependence of ferroelectric phase transition temperature and domain structure on substrate lattice constant and thin film orientation. In cooperation with experimental scientists, these models have been used to provide guidance for molecular beam epitaxy and pulsed laser deposition, and have obtained surprising properties. Their cooperation with Schlom research group of Pennsylvania State University and other collaborators has produced a new discovery: substrate confinement can lead to ferroelectric properties of SrTiO3 _ 3 thin films at room temperature, and SrTiO 3 _ 3 thin films are non-ferroelectric at room temperature without substrate confinement stress. It is found that the base constraint greatly changes the phase diagram of the system and even leads to the formation of new phases.
It is a long-standing problem in ferroelectricity to find out the influencing factors of coercive field (the magnitude of external electric field that makes the net polarization intensity zero). A series of recent work by Chen Longqing's research group on ferroelectric domain inversion reveals the fundamental reason why the coercive field observed in experiments is often much smaller than predicted by previous theories. The theoretical prediction of the research group also provided guidance for his experimental collaborators at the University of California, Berkeley, helping them to understand the stability factors of magnetic domains, and greatly improved the stability of magnetic domains in BiFeO3 materials used in memory devices.
They also extended the work of ferroelectric thin films to multiferroic systems, which involved the coupling between two or more very interesting ferromagnetic phase transitions. These materials have potential application prospects in the manufacture of new memory devices.
Chen Long Qinghe and his collaborators put forward several multi-scale calculation models, and combined first principles, CALPHAD database and phase field simulation of microstructure evolution to construct scientific and engineering calculation tools for alloy design. For example, they showed how to combine three advanced technologies to build a bridge between atomic scale and microstructure: (1) first-principles calculation, (2) mixed space cluster approximation, and (3) diffusion interface phase field model. Recently, they put forward a method that enables people to directly predict the morphology of * * * lattice precipitation phase from first-principles calculation. This involves first-principles calculation, mixed spatial clustering and Monte Carlo simulation. Without any presupposition, they predicted the general precipitation morphology in Al-Cu alloy controlled by strain-induced long-range interaction. The coarsening kinetics of γ precipitated phase in Ni-Al binary alloy was studied by three-dimensional phase field model and CALPHAD approximation. The comprehensive model can quantitatively predict the morphological evolution, average size and size distribution of precipitates with time and composition. These multi-scale concepts are the main idea of a major research project of NASA and Natural Science Foundation of the United States.