High-pressure optical floating-zone growth of Li(Mn,Fe)PO 4 single crystals

Neef, Christoph; Wadepohl, Hubert; Meyer, Hans‐Peter; Klingeler, R.

doi:10.1016/j.jcrysgro.2017.01.046

Cited by 28 publications

(15 citation statements)

References 35 publications

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“…It has been shown [22] for single-crystals LiMn 1−x Fe x PO 4 that the presence of such anisotropic moments evolves with increasing iron content x. One may speculate that the quasi-free moments originate from Fe 2+ anti-site disorder [22,30], whereby some Fe 2+ -ions reside on Li-positions due to the similar radii of the two respective ions. Anti-site disorder in the investigated crystal has been estimated to about 2.3(2)% [22].…”

Section: Discussionmentioning

confidence: 99%

“…One may speculate that the quasi-free moments originate from Fe 2+ anti-site disorder [22,30], whereby some Fe 2+ -ions reside on Li-positions due to the similar radii of the two respective ions. Anti-site disorder in the investigated crystal has been estimated to about 2.3(2)% [22]. The project is supported by Deutsche Forschungsgemeinschaft (DFG) through KL…”

Section: Discussionmentioning

confidence: 99%

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High magnetic field phase diagram and failure of the magnetic Grüneisen scaling in LiFePO4

et al. 2019

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We report the magnetic phase diagram of single-crystalline LiFePO 4 in magnetic fields up to 58 T and present a detailed study of magneto-elastic coupling by means of high-resolution capacitance dilatometry. Large anomalies at T N in the thermal expansion coefficient α imply pronounced magneto-elastic coupling. Quantitative analysis yields the magnetic Grüneisen parameter γ mag = 6.7(5) · 10 −7 mol/J. The positive hydrostatic pressure dependence dT N /dp = 1.46(11) K/GPa is dominated by uniaxial effects along the a-axis. Failure of Grüneisen scaling below ≈ 40 K, i.e., below the peak temperature in the magneto-electric coupling coefficient [1], implies several competing degrees of freedom and indicates relevance of recently observed hybrid excitations [2].A broad and strongly magnetic-field-dependent anomaly in α in this temperature regime highlight the relevance of structure changes. Upon application of magnetic fields B||b-axis, a pronounced jump in the magnetisation implies spin-reorientation at B SF = 32 T as well as a precursing phase at 29 T and T = 1.5 K. In a two-sublattice mean-field model, the saturation field B sat,b = 64(2) T enables the determination of the effective antiferromagnetic exchange interaction J af = 2.68(5) meV as well as the anisotropies D b = −0.53(4) meV and D c = 0.44(8) meV. PACS numbers:In addition to exceptionally high applicability of lithium orthophosphates [3][4][5] for electrochemical energy storage in Li-ion batteries, competing magnetic interactions, magnetic anisotropy and coupling of spin and electric degrees of freedom yield complex magnetic behaviour in LiM PO 4 (M = Mn, Fe, Co, Ni). The rich resulting physics is, e.g., demonstrated by ferrotoroidicity in LiCoPO 4 and LiNiPO 4 [6-8]. In general, depending on the actual transition metal, LiM PO 4 develops long-range antiferromagnetic order at low temperatures and exhibits a large magneto-electric effect in the magnetically ordered phase [1, 9, 10]. The known magnetic phase diagrams of this family are rather complex, featuring incommensurate spin configurations, frustration, and usual magnetic excitations [11-17]. Magnetic phase diagrams have been reported for all lithium orthophosphates [15-17] except for LiFePO 4 . At B = 0 T, LiFePO 4 develops long-range antiferromagnetic order of S = 2 spins of the magnetic Fe 2+ -ions below T N = 50 K [18]. The ordered moment amounts to 4.09 µ B [1, 19] and the spins are mainly directed along the crystallographic b-axis (space group P nma) [19]. Notably, the ground state features a collinear rotation of the spins towards the a-axis as well as spin canting along the c-axis with an overall rotation of the ordered moments of 1.3(1) • off the b-axis [1, 2]. The observed spin canting suggests the presence of Dzyaloshinsky-Moriya (DM) interactions which may account for the magneto-electric coupling in LiFePO 4 . In particular, as spin canting is not compatible with P nma symmetry, a lower crystal symmetry might appear below T N [ 1,20]. Even in the absence of spin canting, an alternative me...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

High magnetic field phase diagram and failure of the magnetic Grüneisen scaling in LiFePO4

et al. 2019

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“…Single crystals of the compositions LiMn 1−x Fe x PO 4 , with x = 0, 0.3, 0.5, 1, were grown by the optical floating zone technique as described in Ref. [14] in detail.…”

Section: Methodsmentioning

confidence: 99%

“…The crystals studied in the present work were grown by the optical-floating zone technique at elevated Argon pressure of 30 bar and display a dark green colour. [14] Crystals used in Ref. [4] were grown in an optical furnace, too, but under ambient pressure.…”

Section: Anisotropic Ionic Conductivity In Lifepomentioning

confidence: 99%

“…In this respect, increase of E A in both direction from 0.62 to 0.78 eV for the a-axis and 0.68 to 0.85 eV for the c-axis might reflect the decrease of the number of anti-site defects from LiFePO 4 to LiMnPO 4 from about 2% to about 1%. [14] Finally, Fig. 8 shows the DC-conductivities related to long-range ionic conductivity, at 30 • C, for all materials and crystallographic directions under study.…”

Section: Doping Dependence Of the Conductivity In Limnmentioning

confidence: 99%

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Anisotropic ionic conductivity of LiMn1−Fe PO4 (0 ≤ x ≤ 1) single crystals

et al. 2020

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We report AC-impedance studies on a series of high-quality LiMn 1−x Fe x PO 4 single crystals with 0 ≤ x ≤ 1. Our results confirm quasi-one-dimensional transport in LiFePO 4 with fast Li-diffusion along the b-axis. The conductivities along the crystallographic b-, c-and a-axis differ by a factor of about 10, respectively. Whereas, the activation energy E A of the effective diffusion process is particularly large for the b-axis and smallest for the a-axis. Remarkably, the b-axis ionic bulk conductivity of LiMn 0.5 Fe 0.5 PO 4 is of the same order of magnitude as in undoped LiFePO 4 , which implies similarly fast Li-transport even upon 50 % Mn-doping which, owing to the higher redox potential of the Mn 3+ /Mn 2+ -couple, yields enhanced energy density in lithium-ion batteries. The overall results of our impedance studies draw a far more complex picture than it would be expected from a simple one-dimensional ionic conductor. Our results suggest a strong contribution of crystal defects in real materials.

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