Evolution of intragranular pores in potassium niobate ceramics during sintering

Potassium niobate ceramics are ideal models for studying perovskite niobates but suffer from poor densification and chemical stability. Here, pure potassium niobate ceramics with a high relative density (99%) are fabricated via hot-pressing, achieving piezoelectric performance comparable to that of pure (K,Na)NbO3 ceramics. Detailed microstructural analysis identifies a high concentration of nanoscale cuboidal intragranular pores. This study clarifies a pore-evolution mechanism: K+-driven lattice diffusion triggers crack formation in the Nb2O5 matrix during calcination. These initial cracks sequentially transform from disordered oblong and oriented elongated shapes into thermodynamically stable cuboidal configurations during further processing. These intragranular pores are the key factor leading to the poor chemical stability of potassium niobate ceramics. This work clarifies the grain growth and pore-evolution mechanisms in potassium niobate ceramics, providing critical insights for enhancing the stability and sintering quality of niobate-based materials. This study achieves high-density potassium niobate ceramics via hot-pressing. It identifies a unique intragranular pore-evolution mechanism driven by lattice diffusion, revealing how these pores dictate the material’s chemical stability.