fig1

Figure 1. Schematic illustration. (A) The solution-reprecipitation process: firstly, α-Si₃N₄ powders, colorants and sintering additives are uniformly mixed; secondly, α-β phase transformation during liquid phase sintering; thirdly, the solution of small β grains and reprecipitation on large β grains, accompanying by the introduction of hollow structures into the large β grains. (B) The generation process of the hollow structures within grains. (C) Proofs for the formation process of the hollow structure in β grain under scanning transmission electron microscopy. (D) Light propagation path in Si₃N₄ ceramics (left) and the schematic illustration of the hollow structure (right).