Effect of Volume Fraction on Coarsening of Y₂BaCuO₅ Particles in Ba-Cu-O Melt

抄録

The effect of the volume fraction of the solid phase (V_f) on coarsening phenomena of Y₂BaCuO₅ (Y211) particles in Ba–Cu–O melt has been investigated. The volume fraction was changed from 10% to 40% by means of controlling of the nominal composition. The size distribution depends on the nominal composition as well. In the samples with hyperperitectic composition (V_f>37%), two different size groups were recognized. On the other hand, it was not observed in the case of hypoperitectic compositions (V_f<37%). The coarsening rate constant (K) also strongly depends on V_f and classified into two groups even in the hypoperitectic compositions. The samples with lower V_f than 15% reveal a higher coarsening rate constants than those with higher V_f than 20%. The phenomena were qualitatively explained by the difference of coarsening mechanisms. Although the zero V_f assumption in a mean field model can be applied for the samples with lower V_f, it became difficult with increasing of V_f and the diffusion mode for the coarsening is changed from the diffusion through a mean field liquid to those among particles.