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/α-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 α-Fe(Si) sheets. A layer of La₅Si₃ phase determined by EDS appeared all along the interface of LaFeSi and 1:13 phase. In addition, La₅Si₃ phase was also found in grain boundary of 1:13 phase grains and La-rich phase was found in grain boundary of α-Fe(Si) sheet. It is believed that La₅Si₃ 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 α-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 α-Fe(Si) layer. It indicated that La and Si elements diffused from LaFeSi sheet to α-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.