Low-temperature negative thermal expansion behavior of LaFe11.2Al1.8-xSix compounds

The cubic NaZn13-type LaFe11.2Al1.8-xSix(x = 0.2, 0.3, 0.4 and 0.5) compounds with different Si content were fabricated by conventional arc-melting method, the structures of which were confirmed by powder X-ray diffraction (XRD) measurement at ambient temperature. Besides, the thermal expansion and magnetic properties of these samples were also researched by means of a strain gage and a physical property measurement system (PPMS). Significantly, it was found that the negative thermal expansion (NTE) behavior have been remarkably enhanced with substituting Al with Si atoms. Furthermore, the NTE operation-temperature window concurrently shifts toward a higher temperature region. The variable temperature XRD results indicate that LaFe11.2Al1.8-xSix retain cubic NaZn13-type structure when temperature varies from 20 K to 270 K, including the temperature region where NTE occurs. The further theoretical analysis combined with magnetic characterization reveal that the improvement of NTE behavior is attributed to the enhancement of Fe-Fe magnetic exchange interactions with doping Si atoms. It is noteworthy that this study displays a new pathway to improve the NTE property of La(Fe,Al)(13)-based compounds at low temperature region, which highlights the potential applications of NTE materials in cryogenic engineering. (C) 2015 Elsevier B.V. All rights reserved.