Spin state crossover in 
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Kazak, N. V.; Платунов, М. С.; Knyazev, Yu. V.; Мolokeev, Maxim S.; Горев, М. В.; Овчинников, С. Г.; Pchelkina, Z. V.; Gapontsev, V. V.; Streltsov, S. V.; Bartolomé, J.; Arauzo, Ana B.; Yumashev, Vladimir V.; Gavrilkin, S. Yu.; Wilhelm, F.; Рогалев, А.

doi:10.1103/physrevb.103.094445

Cited by 23 publications

(11 citation statements)

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“…At this point, it is worthwhile to compare our results with those recently reported by Kazak et al in Ref. 13. In such study, mean bond lengths <M4-O>≈ 1.98 Å and <M2-O>≈ 2.05 Å are reported at 300 K [13].…”

Section: Discussionsupporting

confidence: 78%

“…13. In such study, mean bond lengths <M4-O>≈ 1.98 Å and <M2-O>≈ 2.05 Å are reported at 300 K [13]. This corresponds to a smaller size differentiation of Co ions located at the M 2 and M 4 sites in comparison to our data, suggesting samples with a smaller degree of charge-order at room temperature in comparison to the samples investigated here.…”

Section: Discussionsupporting

confidence: 55%

“…14) are not observed on the calorimetry data of Ref. 13, which rather show a broad maximum at T ≈ 500 K. It is possible that even a small degree of lattice defects is sufficient to pin the defective rungs, preventing the formation of the phase segregated state displayed in Fig. 11(d).…”

Section: Discussionmentioning

confidence: 83%

“…Then, its insulating behavior requires the presence of electronic correlations. A local Hubbard U suffices to make this material insulating [13] and can provide the high energy scale for the chargeordering phenomena we observe.…”

Section: Discussionmentioning

confidence: 97%

“…Particularly, the M =Fe ludwigite shows a combined chargeordering and structural phase transition at 283 K in-volving a zigzag distortion of the 424 ladders below this temperature [6][7][8][9][10]. The M =Co ludwigite, on the other hand, does not show a similar structural phase transition, and all Co 3+ ions appear to occupy only the M 4 site [11][12][13]. Additionally, there is a possible spin-state crossover of the Co 3+ ions, which are presumably in a low-spin configuration in the magnetically ordered phase (T ≤ 43 K) and in a high-spin configuration at higher temperatures (T 200 K) where the Curie-Weiss paramagnetic behavior is established [12,14,15].…”

Section: Introductionmentioning

confidence: 97%

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Structural and spectroscopic investigation of the charge-ordered, short-range ordered, and disordered phases of the Co$_3$O$_2$BO$_3$ ludwigite

Galdino,

Freitas,

Medrano

et al. 2021

Preprint

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Charge-ordering is prone to occur in crystalline materials with mixed-valence ions. It is presumably accompanied by a structural phase transition, with possible exceptions in compounds that already present more than one inequivalent site for the mixed-valence ions in the chargedisordered phase. In this work, we investigate the representative case of the homometallic Co ludwigite Co 2+ 2 Co 3+ O2BO3 (P bam space group) with four distinct Co crystallographic sites [M 1-M 4] surrounded by oxygen octahedra. The mixed-valent character of the Co ions up to at least T = 873 K is verified through x-ray absorption near-edge structure (XANES) experiments. Single crystal x-ray diffraction (XRD) and neutron powder diffraction (NPD) confirm that the Co ions at the M 4 site are much smaller than the others at low temperatures, consistent with a Co 3+ oxidation state at M 4 and Co 2+ at the remaining sites. The size difference between the Co ions in the M 4 and M 2 sites is continuously reduced upon warming above ≈ 370 K, indicating a gradual charge redistribution within the M 4-M 2-M 4 (424) ladder in the average structure. Minor structural anomalies with no space group modification are observed near 475 and 495 K, where sharp phase transitions were previously revealed by calorimetry and electrical resistivity data. An increasing structural disorder, beyond a conventional thermal effect, is noted above ≈ 370 K, manifested by an anomalous increment of XRD Debye-Waller factors and broadened vibrational modes observed by Raman scattering. The local Co-O distance distribution, revealed by Co K-edge Extended X-Ray Absorption Fine Structure (EXAFS) data and analyzed with an evolutionary algorithm method, is similar to that inferred from the XRD crystal structure below ≈ 370 K. At higher temperatures, the local Co-O distance distribution remains similar to that found at low temperatures, at variance with the average crystal structure obtained with XRD. We conclude that the oxidation states Co 2+ and Co 3+ are instantaneously well defined in a local atomic level at all temperatures, however the thermal energy promotes local defects in the charge-ordered configuration of the 424 ladders upon warming. These defects coalesce into a phase-segregated state within a narrow temperature interval (475 < T < 495 K). Finally, a transition at ≈ 500 K revealed by differential scanning calorimetry (DSC) in the iron ludwigite Fe3O2BO3 is discussed.

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Section: Discussionsupporting

confidence: 78%

Section: Discussionsupporting

confidence: 55%