Tunable negative thermal expansion in La(Fe, Si)13/resin composites with high mechanical property and long-term cycle stability

Materials with tunable negative thermal expansion (NTE) are highly demanded in various functional devices. La(Fe, Si)13-based compounds are promising NTE materials due to their outstanding NTE properties. However, their poor mechanical properties and related short service life restrict their practical applications. In this work, epoxy resin with positive thermal expansion is used to synthesize La-Fe-Si/resin composites. The NTE of La-Fe-Si/resin composites can be manipulated by optimizing the La-Fe-Si particle size and resin content, and tailoring resin content could tune the NTE more effectively. The average linear coefficient of thermal expansion of the composites decreases from -275.0 × 10-6 K-1 to -4.9 × 10-6 K-1 over the magnetic transition temperature range as the resin content increases from 3 wt.% to 80 wt.%. In addition, zero thermal expansion is achieved in the La-Fe-Si/resin composite with 20 wt.% resin. The resin would reinforce the binding force by filling the pores between the particles. The La-Fe-Si/resin composite with 80 wt.% resin exhibits highly improved mechanical properties; for example, its compressive strength of 205 MPa is 75% higher than that of the La-Fe-Si/resin composite with 3 wt.% resin. The prepared La-Fe-Si/resin composites can be machined into different shapes for practical applications, such as thin plates, strips, and rods. Furthermore, the La-Fe-Si/resin composites can undergo 1000 thermal cycles without NTE performance degradation and mechanical integrity loss, indicating durable cycle stability. Hence, significantly tunable NTE with high mechanical properties and long-term cycle stability makes La-Fe-Si/resin composites present great application potential as NTE materials.