Pressure-induced spin transition and site-selective metallization in CoCl2

Barreda-Argüeso, José Antonio; Nataf, Lucie; Aguado, Fernando; Hernández, Ignacio Colomer; González, J.; Otero-de-la-Roza, Alberto; Luaña, Vı́ctor; Jia, Yating; Chen, Jin; Kim, Bongjae; Kim, Kyoo; Min, B. I.; Heribert, Wilhem; Jephcoat, A. P.; Rodrı́guez, F.

doi:10.1038/s41598-019-41337-4

Cited by 12 publications

(14 citation statements)

References 48 publications

(48 reference statements)

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“…A similar insulator-to-metal transition has been observed for FeI 2 . CoCl 2 was shown to transition from the 3R polytype (CdCl 2 -type structure) to a 2H polytype (CdI 2 -type modification) at 0.5 GPa followed by another transition to the 1T polytype (CdI 2 -type structure) . Further pressurization results in an insulator-to-metal transition at ∼70 GPa.…”

Section: Layered Transition Metal Halidessupporting

confidence: 71%

Polymorphism in Post-Dichalcogenide Two-Dimensional Materials

2021

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Two-dimensional (2D) materials exhibit a wide range of atomic structures, compositions, and associated versatility of properties. Furthermore, for a given composition, a variety of different crystal structures (i.e., polymorphs) can be observed. Polymorphism in 2D materials presents a fertile landscape for designing novel architectures and imparting new functionalities. The objective of this Review is to identify the polymorphs of emerging 2D materials, describe their polymorph-dependent properties, and outline methods used for polymorph control. Since traditional 2D materials (e.g., graphene, hexagonal boron nitride, and transition metal dichalcogenides) have already been studied extensively, the focus here is on polymorphism in post-dichalcogenide 2D materials including group III, IV, and V elemental 2D materials, layered group III, IV, and V metal chalcogenides, and 2D transition metal halides. In addition to providing a comprehensive survey of recent experimental and theoretical literature, this Review identifies the most promising opportunities for future research including how 2D polymorph engineering can provide a pathway to materials by design.

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Section: Layered Transition Metal Halidessupporting

confidence: 71%

Polymorphism in Post-Dichalcogenide Two-Dimensional Materials

2021

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“…We have shown that the pressure dependence of the CF transitions of Ni 2+ in KNiF 3 all shift to higher energy following the trends of the Tanabe Sugano diagram that was calculated using B = 0.118 eV, 10Dq = 0.908 eV; C/B = 4.4 (10Dq/B = 7.7) at ambient conditions, B and 10Dq varying with pressure as ∂B ∂P = -0.11 meV GPa -1 and ∂10Dq ∂P = 24 meV GPa -1 . The slight pressure decrease of B reflects the strong ionic Ni-F bond, similar to that of the Co-F bond in KCoF 3 ( ∂B ∂P = -0.07 meV GPa -1 ) [21], in comparison to the more covalent Co 2+ −Clor Mn 2+ −Clbonds (both ∂B ∂P = -0.3 meV GPa -1 ) measured in CoCl 2 [45] and [(CH 3 ) 4 N]MnCl 3 [46]. We have shown that the variation of 10Dq with the Ni-F bond distance R follows a potential law as 10Dq = CR -n with an exponent n = 6.6 ± 0.5.…”

Section: Discussionmentioning

confidence: 63%

Pressure dependence of the crystal-field spectrum of KNiF3 : Single and double excitations

Barreda-Argüeso

Rodrı́guez

2021

Phys. Rev. B

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This work investigates the Ni-F distance dependence of the crystal-field (CF) transitions of Ni 2+ in KNiF 3 by high-pressure spectroscopy. All peaks shift to higher energy with pressure according to trends foreseen by the Tanabe-Sugano diagram. At ambient conditions, we obtain Racah and CF splitting parameters of B = 0.118 eV, 10Dq = 0.908 eV; C/B = 4.4 (10Dq/B = 7.7). B and 10Dq vary with pressure as ∂B ∂P = -0.11 meV GPa -1 and ∂10Dq ∂P = 24 meV GPa -1 . Similar to KCoF 3 , the slight decrease of B with pressure reflects the strong ionic character of the Ni-F bond and its high stability against compression. We have correlated the measured pressure dependence of 10Dq with the Ni-F bond distance, showing that it follows a potential law as 10Dq = CR -n with an exponent n = 6.6 ± 0.5, thus providing experimental data for checking the suitability of theoretical models aiming to explain the slight deviations of observed R dependencies of 10Dq from the CF theory (n = 5). We have applied the experimental 10Dq(R) relationship to determine the real Ni-F bond distances in fluoroperovskites ABF 3 : Ni 2+ from the spectroscopically measured 10Dq as an alternative method for determining bond distances, R Ni−F , in impurity systems. We show that the so-obtained R Ni−F deviates from the bond distance of the host site, R B−F , proportionally to the difference R B−F − R 0 , with R 0 being the sum of ionic radii R F − + R Ni 2+ . The behavior is compared to that found for Mn 2+ along the fluoroperovskite series ABF 3 : Mn 2+ . Finally, weak UV peaks observed below the charge-transfer band gap (E g 10 eV) in the absorption spectrum, the assignment of which still remains controversial, have been assigned to single and double excitation transitions. The assignment was unveiled on the basis of their energy and pressure shift.

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“…However, resistivity measurements have shown that bulk PbCrO 4 remains as a semiconductor material at least up to 35 GPa . In the case of PbCrO 4 nanorods, we have observed a darkening of the sample at the phase transition, which might be a hint that metallization could take place under further compression …”

mentioning

confidence: 70%

“…11 In the case of PbCrO 4 nanorods, we have observed a darkening of the sample at the phase transition, which might be a hint that metallization could take place under further compression. 33 In order to explore the possible metallization of AgMnO 4type PbCrO 4 , we have carried out band-structure calculations. The calculated band structure and electronic density of states at two different pressures are shown in Figure 7.…”

mentioning

confidence: 99%

Putting the Squeeze on Lead Chromate Nanorods

Yuan

Rodríguez‐Hernández

Múñoz

et al. 2019

J. Phys. Chem. Lett.

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We have studied by means of X-ray diffraction and Raman spectroscopy the high-pressure behavior of PbCrO 4 nanorods. We have found that these nanorods follow a distinctive structural sequence that differs from that of bulk PbCrO 4 . In particular, a phase transition from a monoclinic monazite-type PbCrO 4 to a novel monoclinic AgMnO 4 -type polymorph has been discovered at 8.5 GPa. The crystal structure, Raman-active phonons, and compressibility of this novel high-pressure phase are reported for the first time. The experimental findings are supported by ab initio calculations that provide information not only on structural and vibrational properties of AgMnO 4 -type PbCrO 4 but also on the electronic properties. The discovered phase transition triggers a band gap collapse and a subsequent metallization at 44.2 GPa, which has not been observed in bulk PbCrO 4 . This suggests that nanoengineering can be a useful strategy to drive metallization under compression.

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Pressure-induced spin transition and site-selective metallization in CoCl2

Cited by 12 publications

References 48 publications

Polymorphism in Post-Dichalcogenide Two-Dimensional Materials

Polymorphism in Post-Dichalcogenide Two-Dimensional Materials

Pressure dependence of the crystal-field spectrum of KNiF3 : Single and double excitations

Putting the Squeeze on Lead Chromate Nanorods

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