The dynamics of spontaneous hydrogen segregation in LaFe13−xSixHy

Baumfeld, Oliver L.; Gercsi, Z.; Krautz, Maria; Gutfleisch, Oliver; Sandeman, K. G.

doi:10.1063/1.4879099

Cited by 20 publications

(11 citation statements)

References 26 publications

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“…at x > 2.4, and |∆S iso | significantly decreases 13 . It has been found that T C can be achieved above room temperature (RT) by interstitial H incorporation 15,[26][27][28][29][30][31][32][33] . T C of the hydrogenated compounds can be precisely tuned near RT by varying Mn substitution [34][35][36][37][38][39] .…”

Section: Introductionmentioning

confidence: 99%

Determining the vibrational entropy change in the giant magnetocaloric material LaFe11.6Si1.4 by nuclear resonant inelastic x-ray scattering

et al. 2018

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Magnetocaloric LaFe13−xSix-based compounds belong to the outstanding materials with potential for efficient solid-state refrigeration. We have performed temperature-dependent 57 Fe nuclear resonant inelastic X-ray scattering measurements (in a field µ0H of ∼ 0.7 T) of the vibrational (phonon) density of states, VDOS, in LaFe11.6Si1.4 across the metamagnetic isostructural first-order phase transition at TC ∼ 192 K from the low-temperature ferromagnetic (FM) to the high-temperature paramagnetic (PM) phase, in order to determine the change in thermodynamic properties of the Fe lattice at TC . The experimental results are compared with density-functional-theory (DFT)-based first-principles calculations using the fixed-spin moment (FSM) approach. Our combined experimental and theoretical results reveal distinct and abrupt changes in the VDOS of the Fe sublattice across TC , occurring within a small temperature interval of ∆T ≤ 12 K around TC . This indicates that strong magnetoelastic coupling (at the atomic scale) is present up to TC , leading to a pronounced lattice softening (phonon red-shift) in the PM phase. These changes originate from the itinerant electron magnetism associated with Fe and are correlated with distinct modifications in the Fe-partial electronic density of states, D(EF ), at the Fermi energy, EF . From the experimental VDOS we can infer an abrupt increase (jump) in the Fe-partial vibrational entropy ∆S vib of + 6.9 ± 2.6 J/(kg K) and in the vibrational specific heat ∆C vib of + 2.7 ± 1.6 J/(kg K) upon heating. The increase in magnitude of the vibrational entropy |∆S vib |= 6.9 J/(kg K) of the Fe sublattice at TC upon heating is substantial, if compared with the magnitude of the isothermal entropy change |∆Siso| of 14.2 J/(kg K) in a field change ∆B from 0 to 1 T, as obtained from isothermal magnetization measurements on our sample and using the Maxwell relation. We demonstrate that ∆S vib obtained by NRIXS is a sizable quantity and contributes directly and cooperatively to the total entropy change ∆Siso at the phase transition of LaFe13−xSix. * Corresponding author. Electronic address:

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Section: Introductionmentioning

confidence: 99%

Determining the vibrational entropy change in the giant magnetocaloric material LaFe11.6Si1.4 by nuclear resonant inelastic x-ray scattering

et al. 2018

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“…However, several studies have shown that, for H composition lower than 1.5 H/f.u. and with T C close to room temperature, there is a splitting into two hydride phases with low and high H concentrations after few hours or weeks at RT [55,74,75]. The sample is no more homogeneous and the magnetic entropy variation is split in two peaks.…”

Section: Combination Of Substitution and Light Element Insertionmentioning

confidence: 99%

Tuning the Magnetocaloric Properties of the La(Fe,Si)13 Compounds by Chemical Substitution and Light Element Insertion

Paul‐Boncour

Bessaïs

2021

Magnetochemistry

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LaFe13−xSix compounds exhibit a giant magnetocaloric effect and they are considered as a good magnetocaloric working substance for an environmentally friendly cooling technique. Nevertheless as the Curie temperature TC is around 200 K, it is necessary to tune TC near room temperature for magnetic refrigeration. In this work we present a review of the various methods of synthesis and shaping of the LaFe13−xSix type compounds as well as the influence of chemical substitution, light element insertion or combination of both on TC, magnetic entropy and adiabatic temperature variation (ΔSM and ΔTad), and stability upon cycling. The advantages and drawbacks of each method of preparation and type of element substitution/insertion are discussed. The implementation of these NaZn13 type materials in active magnetic refrigerator is presented and their performances are compared to that of Gd in prototypes.

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“…Although the amount of hydrogen absorbed offers the theoretical potential of targeted TC control, only full hydrogenation is practicable for such first-order (large volume change, sharp magnetic phase transition) compositions due to phase-separate effect where two separate spatial regions with distinctly differing TCs are formed when the material is thermally cycled through the magnetic transition or when it sits close to TC for several days. The origin of this instability is the lattice expansion in the FM state, prompting hydrogen atoms to diffuse from the PM into FM regions of the material that transform first [20]. Partial hydrogenation therefore results in undesirable heterogeneous changes to the samples' properties within very short time scales [21,22].…”

Section: Two Vital Considerations Towards the Implementation Of Magnementioning

confidence: 99%

“…the M(T)properties of sample (A6) have been measured after two months at T = TC + 10 K, then 24 h and 48 h at TC (= 285 K), timescales over which significant hydrogen distribution instability is present in first-order compositions[20], and then finally after repeated fast cycling (15 cycles) across the transition. As shown from the M(H) derivative, only one transition is observed and this is unchanged after all 4 protocols, demonstrating that the properties of partially hydrided samples are stable, behaviour we expect to be general for materials with second-order transitions.…”

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confidence: 99%

Fine control of Curie temperature of magnetocaloric alloys La(Fe,Co,Si)13 using electrolytic hydriding

et al. 2020

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This work demonstrates precision control of hydrogen content in La(Fe,Co,Si)13H for the development of environmentally friendly magnetocaloric-based cooling technologies, using an electrolytic hydriding technique. We show the Curie temperature, a critical parameter which directly governs the temperature window of effective cooling, can be varied easily and reproducibly in 1 K steps within the range 274 K to 402 K. Importantly, both partially (up to 10%) and fully hydrided compositions retain favorable entropy change values comparable to that of the base composition. Crucially, we show in these second-order phase transition compounds, partial hydriding is stable and not susceptible against phase separation.

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The dynamics of spontaneous hydrogen segregation in LaFe13−xSixHy

Cited by 20 publications

References 26 publications

Determining the vibrational entropy change in the giant magnetocaloric material LaFe11.6Si1.4 by nuclear resonant inelastic x-ray scattering

Determining the vibrational entropy change in the giant magnetocaloric material LaFe11.6Si1.4 by nuclear resonant inelastic x-ray scattering

Tuning the Magnetocaloric Properties of the La(Fe,Si)13 Compounds by Chemical Substitution and Light Element Insertion

Fine control of Curie temperature of magnetocaloric alloys La(Fe,Co,Si)13 using electrolytic hydriding

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