Formation of 1:13 Phase in La(Fe,Si)13-Based Compounds by Diffusion of LaFe,Si/\alpha-Fe(Si) Couple.

Formation mechanism of the 1:13 phase in \ La(\ Fe,\ Si)13 compounds has been investigated by the diffusion of \ LaFeSi/\alpha-\ Fe(\ Si) couple at 1353 K and 1443 K. After annealing at 1353 K for 12 days, 0.8 mm thick 1:13 phase was obtained between LaFeSi and \alpha-\ Fe(\ Si) sheets. A layer of \ La5{\ {Si}}3 phase determined by EDS appeared all along the interface of LaFeSi and 1:13 phase. In addition, \ La5{\ {Si}}3 phase was also found in grain boundary of 1:13 phase grains and La-rich phase was found in grain boundary of \alpha-\ Fe(\ Si) sheet. It is believed that \ La5{\ {Si}}3 phase and grain boundaries working as rapid diffusion paths were important for the formation of 1:13 phase in \ La(\ Fe,\ Si)13 compounds. 1:13 phase mainly formed in the \alpha-\ Fe(\ Si) master alloy sheet. In addition, large grains of 1:13 phase were close to the LaFeSi sheet and small grains of 1:13 phase were close to \alpha-\ Fe(\ Si) layer. It indicated that La and Si elements diffused from LaFeSi sheet to \alpha-\ Fe(\ Si) sheet in the formation process of 1:13 phase. There was an endothermic peak at 207 K in the DSC curve of the 1:13 phase obtained from diffusion couple annealed at 1353K. It indicated the occurrence of magnetic phase transition. [ABSTRACT FROM PUBLISHER]