Magnetocaloric effect and refrigerant capacity in Sr-doped Eu8Ga16Ge30 type-I clathrates

Abstract

Magnetic properties, the magnetocaloric effect ͑MCE͒ and refrigerant capacity ͑RC͒ were investigated in Eu 8 Sr 8−x Ga 16 Ge 30 ͑x=0,4͒ type-I clathrates. The substitution of Sr for Eu decreases the Curie temperature ͑T C ͒ and saturation magnetization ͑M S ͒ from 35 K and 65 emu/g for the x = 0 composition to 15 K and 35 emu/g for the x = 4 composition. This is attributed to the increase in the Eu-Eu distance with Sr substitution. The large MCE and RC are achieved in both specimens. For a field change of 3 T, the MCE and RC reach the largest values of 5.8 J / kg K and 127.6 J/kg for x = 0 composition and 4.3 J / kg K and 72.1 J/kg for x = 4 composition. The broadening of the MCE curves is likely associated with the ordering of the magnetic moments of Eu that occurs below 10 K. The large values of MCE and RC, in addition to the absence of thermal and field hysteresis indicate that these clathrate materials are very interesting for cryogenic magnetic refrigeration applications.

Origin of the magnetic anomaly and tunneling effect of europium on the ferromagnetic ordering inEu8−xSrxGa16Ge30Phan1, Franco2, Chaturvedi3 et al. 2011Phys. Rev. B730260View full textAdd to dashboardCite

“…7 However, the case may be different for the Eu 8 Ga 16 Ge 30 type-I clathrate. [4][5][6]8 In this material, the shortest distances for Eu2-Eu2, Eu2-Eu1, and Eu1-Eu1 are 5.23Å, 5.62Å, and 10.7Å, respectively. 5 The Eu-Eu distance in the [111] direction is 9.27Å.…”

“…1 Incorporating rare-earth elements with large magnetic moments as "guest" atoms into an adequate semiconducting host framework has made these materials also interesting for thermomagnetic applications. [4][5][6][7][8] Among the existing clathrates, the composition Eu 8 Ga 16 Ge 30 is an example in which the sites for the guest atoms are fully occupied by Eu. 4,5 The Eu 8 Ga 16 Ge 30 composition can form in two completely different clathrate structure types.…”

“…The large separation distance between neighboring Eu 2+ ions (>5.23Å) excludes the direct exchange interaction between the localized 4f moments and suggests the long-range Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction via the charge carriers as the key mechanism for the occurrence of the ferromagnetism in these materials. [4][5][6][7][8] Since the shortest distance between Eu 2+ ions in the type-I clathrate (∼5.23Å) is smaller than that of the type-VIII clathrate (∼5.562Å), the former possesses a higher Curie temperature (T C ∼ 35 K) compared with that of the latter (T C ∼ 13 K). 5,7 Using the standard formulation for the exchange Hamiltonian and the carrier concentrations at T C determined from the Hall constants, Paschen et al 5 have argued that ferromagnetism should exist for Eu-Eu distances under 6.5Å for the type-I clathrate and 10Å for the type-VIII clathrate.…”

Structural and thermodynamic properties of Cu‐doped Sn‐based single‐crystalline clathrates

“…The performance of a thermoelectric material depends on the figure of merit ZΤ = α 2 σΤ / κ , where α is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, T is the absolute temperature, and a high ZT is the value that thermoelectric material must possess . In recent decades, the performance of the thermoelectric materials has significantly improved through intensive research ; however, the ZT value is still maintained at around unity and is still difficult to be applied. Therefore, researching high‐performance thermoelectric materials is a vital task in developing clean energy.…”

Rapid crystal growth of type-II clathrates A8Na16Si136 (A = K, Rb, Cs) by spark plasma sintering

“…[6][7][8] As a result, they are of interest for a variety of potential technological applications, including solid state energy conversion, [1][2][3]9 photovoltaics, 10,11 magnetocalorics, [12][13][14] superconductivity, [15][16][17] and as the anode for Li-ion batteries. [18][19][20] Due to this scientific interest and technological importance an understanding of the fundamental structural and physical properties of inorganic clathrates is essential.…”