  Cracking in La(Fe,Si)13-based magnetocaloric materials has been observed to
predominantly form around La-rich (La2O3) particles and pose a threat to their
long-term structural integrity. To understand the formation of these cracks,
FIB cross-sectional polishing followed by SEM characterisation was employed to
study local microstructural evolution after air exposure. Results suggest that
volume expansion and internal degradation associated with a chemical reaction
between La2O3 particles and water/moisture can lead to crack nucleation in the
1:13 phase adjacent to La-rich particles. This observation indicates that the
formation of La-rich phase should be suppressed, or their size minimised during
material processing to ensure the long-term structural integrity of
La(Fe,Mn,Si)13 magnetocaloric materials.
