Low-temperature abnormal thermal expansion property of Mn doped cubic NaZn₁₃-type La(Fe, Al)₁₃ compounds

Tailoring Negative Thermal Expansion via Tunable Induced Strain in La–Fe–Si-Based Multifunctional Material

“…LaFe 11.9 Mn 0.27 Si 1.29 H x has the NaZn13-type crystal structure (space group Fm-3c), where the Fe atoms, 8b (Fe­(I)) and 96i (Fe­(II)), occupy two nonequivalent 8b (Fe­(I)) and 96i (Fe­(II)) sites; Si atoms preferentially occupy Fe­(II) sites; , Mn atoms tend to occupy equally both Fe­(I) and Fe­(II) sites; , and the hydrogen atoms lie at interstitial sites (see Figure S1 in the Supporting Information). The Rietveld refinements against all X-ray diffractograms at 273.6 K reveal the expected NaZn 13 -type crystal structure and a minority phase fraction of α-Fe (space group Im-3m ), which is commonly observed in samples prepared by this route .…”

“…Along these transitions, the crystal structure is retained, but the unit cell volume contracts by 3000–30,000 ppm typically over a <50 K temperature interval. ,,,− To act as compensators, NTE materials should have a more gradual change of volume over a larger temperature window, akin to the typical changes on standard PTE materials. Fortunately, it is possible to tune and shape the profile of the magnetization versus temperature curves (namely, the T C and the dM / dT ) by tuning both extrinsic (pressure and magnetic field) ,− and intrinsic (stoichiometry) properties. ,,,,− Recently, there have been remarkable examples of thermal expansion control via chemical substitutions, where the typically abrupt NTE behavior is smoothed across a wider temperature window. ,,,,− For example, by replacing Fe by Co and Mn, or by adjusting the Si/Fe ratio, or even by electrolytic hydrogenating La–Fe–Si, Li’s group has successfully been able to tune the operational temperature and smooth out La–Fe–Si sharp volume transition. ,,− …”

“…The La­(Fe 1– x ,Si x ) 13 -derived compounds are very well known for their giant magnetocaloric effect and NTE behavior. ,,,,,,− Their crystal structure is cubic with Fm-3c space group, and they display a ferromagnetic-to-paramagnetic (FM-PM) isostructural transition, corresponding to a low-temperature high-magnetization (ordered) state that evolves into a high-temperature low-magnetization (disordered) state as the temperature is increased across their T C . Along these transitions, the crystal structure is retained, but the unit cell volume contracts by 3000–30,000 ppm typically over a <50 K temperature interval. ,,,− To act as compensators, NTE materials should have a more gradual change of volume over a larger temperature window, akin to the typical changes on standard PTE materials.…”