Evolution of grain growth mechanisms and size inhomogeneity in pressureless sintered BaTiO3 nanopowders with increasing sintering temperature

This study investigates the grain growth kinetics of spherical BaTiO 3 nanopowders (average size: 160 nm) during pressureless sintering at 1000 ℃ and 1300 ℃. To accurately elucidate the underlying growth mechanisms, a refined model–designated as G i , t –was proposed by incorporating a simplified redefinition of the initial grain size ( G 0 ) to decouple pre-isothermal growth. The kinetic parameters, n and K , were determined using both log-linear fitting and Python-based non-linear regression analysis. Both methodologies yielded calculated values in excellent agreement with experimental data across various isothermal holding times ( R 2 > 0.98). As the sintering temperature increased, the kinetic coefficient ( K ) rose significantly, while the grain growth exponent ( n ) decreased from 3.5 to 1.7, indicating a clear mechanistic transition. Specifically, the activation energy derived from the G i , t model (161.0 kJ/mol) was found to be more physically representative of intrinsic grain growth than conventional models. Microstructural and statistical analyses revealed that at 1000 ℃, grain growth remained unimodal, dominated by surface and grain boundary diffusion. However, at 1300 ℃, the distribution transitioned to a bimodal profile after prolonged holding, signaling the onset of abnormal grain growth. These findings demonstrate that the G i , t model provides a robust and precise framework for predicting microstructural evolution, offering critical insights into the fundamental mechanisms required to achieve high-fidelity control over grain size uniformity in advanced ceramic sintering.