Pressure-induced valence transition in the mixed-valence (Sm1/3Ca2/3)2.75C60 fulleride

Yoshikane, Naoya; Matsui, Keisuke; Nakagawa, Takeshi; Terzidou, Anastasia; Takabayashi, Yasuhiro; Yamaoka, H.; Hiraoka, Nozomu; Ishii, Hirofumi; Arvanitidis, J.; Prassides, Kosmas

doi:10.1039/d0qm00707b

Cited by 6 publications

(13 citation statements)

References 39 publications

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“…Confining attention to x = 0.65 and x = 0.7 samples, two distinct peaks, separated by the same energy difference of about 8 eV, were found in the XAS spectra. This unambiguously evidences the mixed-valence character of Sm since the high-energy peak at 6722 eV corresponds to the trivalent Sm (Sm 3+ ) [29,30]. In addition, the intensity of the high-energy peak is regularly enhanced with increasing Sm content x without an energy shifts.…”

Section: Resultsmentioning

confidence: 54%

“…To address the issue of the evolution of Sm valence states with Sm content x, the XAS spectra at the Sm L 3 -edge are displayed in Figure 1d for La 2.6 Sm 0.4 Te 4 , La 2.35 Sm 0.65 Te 4 , and La 2.3 Sm 0.7 Te 4 composited with 10 vol.% Ni samples. For the sample with x = 0.4, only a single peak was observed at 6714 eV, corresponding to the divalent Sm (Sm 2+ ) [29,30]. Confining attention to x = 0.65 and x = 0.7 samples, two distinct peaks, separated by the same energy difference of about 8 eV, were found in the XAS spectra.…”

Section: Resultsmentioning

confidence: 96%

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Thermoelectric Performance Optimization of n-Type La3−xSmxTe4/Ni Composites via Sm Doping

Song

Liu

et al. 2022

Energies

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La3Te4-based rare-earth telluride is a kind of n-type high-temperature thermoelectric (TE) material with an operational temperature of up to 1273 K, which is a promising candidate for thermoelectric generators. In this work, the Sm substitution in La3−xSmxTe4/Ni composites is reported. The electrical transport property of La3−xSmxTe4 is modified by reducing carrier concentration due to the substitution of Sm2+ for La3+. The electric thermal conductivity decreases by 90% due to carrier concentration reduction, which mainly contributes to a reduction in total thermal conductivity. Lattice thermal conductivity also decreases by point-defect scattering by Sm doping. Meanwhile, based on our previous study, compositing nickel improves the thermal stability of the La3 − xSmxTe4 matrix. Finally, combined with carrier concentration optimization and the decreased thermal conductivity, a maximum zT of 1.1 at 1273 K and an average zTave value of 0.8 over 600 K–1273 K were achieved in La2.315Sm0.685Te4/10 vol.% Ni composite, which is among the highest TE performance reported in La3Te4 compounds.

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Section: Resultsmentioning

confidence: 54%

Section: Resultsmentioning

confidence: 96%

Thermoelectric Performance Optimization of n-Type La3−xSmxTe4/Ni Composites via Sm Doping

Song

Liu

et al. 2022

Energies

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“…What is notable here is that the structural renormalization occurs precisely in the same pressure range in which the (Sm 1/3 Ca 2/3 ) 2.75 C 60 sample exhibits a first-order reversible electronic phase transition accompanied by a drastic increase of the average Sm valence by ∼20% (from +2.33 to +2.71). 23 Figure 6 displays both the diffraction and the spectroscopy results unambiguously establishing their one-to-one correspondence, thereby signifying direct coupling between the lattice and electronic degrees of freedom in these materials.…”

Section: Discussionmentioning

confidence: 74%

“…23 The pressure-induced valence transition is reversible but strongly hysteretic upon depressurization with a hysteresis width of ∼2.5 GPa, indicative of the first-order nature of the transition. 23 Although there had been no highpressure diffraction data available for this composition, the observed electronic instability occurred in the vicinity of the pressure range in which the parent material, Sm 2.75 C 60 , showed a large lattice size decrease 16 and the appearance of metallic behavior. 17 This was taken as tentative evidence of the potentially strong coupling between the valence and the elastic properties of the material.…”

Section: Introductionmentioning

confidence: 98%

Isosymmetric Lattice Collapse in Mixed-Valence Rare-Earth Fullerides at High Pressure─Coupling of Lattice and Electronic Degrees of Freedom

et al. 2023

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The orthorhombic-structured (Sm1/3Ca2/3)2.75C60 is a member of the family of rare-earth metal intercalated C60 fullerides with stoichiometry, RE2.75C60 (RE = rare-earth metal). At ambient conditions, it crystallizes with the formation of a 2a × 2a × 2a (a ∼ 14 Å) supercell of the face-centered cubic (fcc) A3C60 (A = alkali metal) unit cell. The superstructure is stabilized by the long-range ordering of tetrahedral-site Sm/Ca metal defects (O phase). Synchrotron X-ray powder diffraction measurements at high pressure and ambient temperature reveal that (Sm1/3Ca2/3)2.75C60 is a compressible solid with a bulk modulus, K 0 = 24(1) GPa, that transforms to a more densely packed isostructural high-pressure O′ phase above ∼4 GPa. The first-order phase transition retains the formation of the superstructure and is accompanied by a discontinuous lattice size decrease (ΔV/V ∼ 2%). The O′ phase is stabilized by the release of the steric crowding that develops upon compression; the Sm/Ca metal ions, which reside in the tetrahedral and octahedral holes of the fulleride sublattice, shift from their off-centered positions at low pressure (O phase) to nest at the centers of the interstices (O′ phase). The nearly exact coincidence of the pressure response of the reversible hysteretic O ↔ O′ phase transformation with that of the samarium valence transition from +2.33(2) to +2.71(3), as established before by synchrotron X-ray absorption spectroscopy, unambiguously establishes an intimate link between the crystal and electronic structures of the (Sm1/3Ca2/3)2.75C60 fulleride.

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“…This suggests that the exchange interaction plays a role in the alignment associated with these features. It is common to use XAS studies of the Sm L 3 edge to determine the average valence of the samarium in mixed valence systems [174][175][176][177]. However, these XAS studies typically leave little ambiguity about the existence of two clear absorption features.…”

Section: Exploring the Possibility Of Mixed Valence Smmentioning

confidence: 99%

Rare-earth nitride solid solutions

Miller¹

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Improvements to computing efficiency are required to offset the energy costs of increasing demand on cloud computing data centres (the cost of which is currently borne by fossil fuel energy production, and thus, the environment) [4]. The 20th-century technologies that currently support our heavy use of computers are unable to keep providing efficiency improvements due to the fundamental limits associated with the physics that they rely on to operate, meaning that new physical mechanisms are required [5–8]. Improvements to computing efficiency are offered by superconducting computing, but the implementation of this technology requires cryogenically-viable memory, which is not currently available [9, 10]. The research field of spintronics promises devices with plausible improvements over current memory technologies, but these devices require materials in which complex properties can be controlled [11, 12]. The rare-earth nitrides are a series of intrinsic ferromagnetic semiconductors, that have been included in device architectures with some success [13–15]. Their combination in a solid solution offers control over the magnetic and electrical properties of a homogenous single-layer thin film, allowing the fine-tuning of the properties to meet the requirements of application. Understanding the material properties of rare-earth nitride solid solutions is the central topic of this thesis. This thesis documents research into the properties of Gdx Sm1−x N, a solid solution of the rare-earth nitrides GdN and SmN. We present magnetometry, x-ray magnetic circular dichroism (XMCD), and Hall effect measurements on a series of GdxSm1−xN films. Magnetometry results show a linear dependence of the saturation magnetisation on the Gd fraction of the films, x, over much of the range 0 ≤ x ≤ 1. Further results show that GdxSm1−xN films with a low Gd fraction (x ≤ 0.3) exhibit perpendicular magnetic anisotropy. Films for which x ≤ 0.2 show a deviation from the linear dependence of the saturation magnetisation on x, and extremely low magnetic moments. This low moment results, in part, from the opposition of the net moment of the Gd3+ and Sm3+ ions. The opposition of the net moment comes from the orbital-dominant magnetism of the Sm3+ ion and the alignment of the Gd3+ and Sm3+ spins by the exchange interaction (which is confirmed by XMCD). This combination of the orbital-dominant magnetism of the Sm3+ ion and the alignment of the Gd3+ and Sm3+ spins by the exchange interaction also causes there to be compositions of GdxSm1−xN for which the net magnetic moment or the net angular momentum of the solution is zero. These “compensation points” are familiar from other classes of material generally held to be promising for similar applications [16, 17]. Measurements of XMCD show an increasing spin polarisation of Sm3+ as a function of x, changing where one expects to find the angular momentum compensation point xa. The value of xa is estimated with reference to the XMCD measurements to be xa = 0.245. Furthermore, measurements of the anomalous Hall effect are used to locate the compensation point of the net magnetic moment, xc , which is found to be xc = 0.05.

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Pressure-induced valence transition in the mixed-valence (Sm_1/3Ca_2/3)_2.75C₆₀ fulleride

Abstract: (Sm⅓Ca⅔)2.75C60 is a member of the family of non-stoichiometric strongly-correlated rare-earth fullerides, (Sm1-xCax)2.75C60 (0 ≤ x ≤ 1), in which an orthorhombic 222 supercell of the face-centred cubic (fcc) unit...

Cited by 6 publications

References 39 publications

Thermoelectric Performance Optimization of n-Type La3−xSmxTe4/Ni Composites via Sm Doping

Thermoelectric Performance Optimization of n-Type La3−xSmxTe4/Ni Composites via Sm Doping

Isosymmetric Lattice Collapse in Mixed-Valence Rare-Earth Fullerides at High Pressure─Coupling of Lattice and Electronic Degrees of Freedom

Rare-earth nitride solid solutions

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