Structure and stability of SmCo5

The structure of SmCo
5
has been investigated between 500°C and its melting point. It is found that SmCo
5
is a composite of two phases. One of them is unstable and decomposes below 1150°C giving rise to the neighboring phase Sm
2
Co
17
. No traces of Sm
2
Co
7
have been observed during this decomposition. The reaction of SmCo
5
with the container materials is discussed. The potential importance of RCo
5
compounds of the CaZn
5
- type structure for the manufacture of permanent magnets has resulted in intensive research on these materials. These materials have extremely high energy products and coercive fields. Several reports on the structure and stability of SmCo
5
have been presented in recent years. On the basis of measurements of the coercive field, Westendorp [1,2] concludes that SmCo
5
is a single phase above 1080°C and below this temperature a second phase precipitates out. The size of the particles of this precipitated phase controls the coercive field. Den Broeder et al. [3] and Buschow [4] have reported a eutectoid decomposition of SmCo
5
at about 750°C (SmCo
5
= Sm
2
Co
7
+ Sm
2
Co
17
). Although they detect the presence of Sm
2
Co
7
and Sm
2
Co
17
by metallographic methods, they are unable to find any traces of Sm
2
Co
7
by X-ray diffraction techniques. In this paper we report on the structure and stability of SmCo
5
at various temperatures and its reaction with various container materials.