1
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Santamaría G, Fernández-Ruiz T, García-Lastra JM, García-Fernández P, Sánchez-Movellán I, Moreno M, Aramburu JA. Understanding Pressure Effects on Structural, Optical, and Magnetic Properties of CsMnF 4 and Other 3d n Compounds. Inorg Chem 2024; 63:13231-13243. [PMID: 38984802 PMCID: PMC11271007 DOI: 10.1021/acs.inorgchem.4c00599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2024] [Revised: 06/10/2024] [Accepted: 06/12/2024] [Indexed: 07/11/2024]
Abstract
The pressure dependence of structural, optical, and magnetic properties of the layered compound CsMnF4 are explored through first-principles calculations. The structure at ambient pressure does not arise from a Jahn-Teller effect but from an orthorhombic instability on MnF63- units in the tetragonal parent phase, while there is a P4/n → P4 structural phase transition at P = 40 GPa discarding a spin crossover transition from S = 2 to S = 1. The present results reasonably explain the evolution of spin-allowed d-d transitions under pressure, showing that the first transition undergoes a red-shift under pressure following the orthorhombic distortion in the layer plane. The energy of such a transition at zero pressure is nearly twice that observed in Na3MnF6 due to the internal electric field and the orthorhombic distortion also involved in K2CuF4. The reasons for the lack of orthorhombic distortion in K2MF4 (M = Ni, Mn) or CsFeF4 are also discussed in detail. The present calculations confirm the ferromagnetic ordering of layers in CsMnF4 at zero pressure and predict a shift to an antiferromagnetic phase for pressures above 15 GPa consistent with the reduction of the orthorhombicity of the MnF63- units. This study underlines the usefulness of first-principles calculations for a right interpretation of experimental findings.
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Affiliation(s)
- Guillermo Santamaría
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain
- Donostia
International Physics Center (DIPC), 20018 Donostia, Euskadi, Spain
- Laboratory
for Chemistry of Novel Materials, University
of Mons, 7000 Mons, Belgium
| | - Toraya Fernández-Ruiz
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain
| | - Juan María García-Lastra
- Department
of Energy Conversion and Storage, Technical
University of Denmark, Anker Engelunds Vej. Building 301, 2800 Kgs. Lyngby, Denmark
| | - Pablo García-Fernández
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain
| | - Inés Sánchez-Movellán
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain
| | - Miguel Moreno
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain
| | - José Antonio Aramburu
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain
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2
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Fernández-Ruiz T, Sánchez-Movellán I, García-Lastra JM, Moreno M, Aramburu JA, García-Fernández P. Strain-Phonon Cooperation as a Necessary Ingredient to Understand the Jahn-Teller Effect in Solids. J Phys Chem Lett 2024; 15:6476-6481. [PMID: 38869224 PMCID: PMC11215767 DOI: 10.1021/acs.jpclett.4c01256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2024] [Revised: 06/12/2024] [Accepted: 06/12/2024] [Indexed: 06/14/2024]
Abstract
Spatial degeneracy is the cause of the complex electronic, geometrical, and magnetic structures found in a number of materials whose more representative example is KCuF3. In the literature the properties of this lattice are usually explained through the Kugel--Khomskii model, based on superexchange interactions. Here we provide rigorous theoretical and computational arguments against this view proving that structural and magnetic properties essentially arise from electron-vibration (vibronic) interactions. Moreover, based on the work of Öpik and Pryce, we show that the coupling between lattice (homogeneous strain) and motif (phonons) distortions is essential to understand the main stable configurations of the lattice. Using this information, we predict a new low-energy phase in KCuF3 that could strongly alter its properties and provide guidance on how to stabilize it through strain engineering.
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Affiliation(s)
- Toraya Fernández-Ruiz
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional, Avenida de los
Castros s/n, 39005 Santander, Spain
| | - Inés Sánchez-Movellán
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional, Avenida de los
Castros s/n, 39005 Santander, Spain
| | - Juan María García-Lastra
- Department
of Energy Conversion and Storage, Technical
University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Miguel Moreno
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional, Avenida de los
Castros s/n, 39005 Santander, Spain
| | - José Antonio Aramburu
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional, Avenida de los
Castros s/n, 39005 Santander, Spain
| | - Pablo García-Fernández
- Departamento
de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional, Avenida de los
Castros s/n, 39005 Santander, Spain
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3
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Carrasco-Busturia D, Sánchez-Movellán I, Tygesen AS, Bhowmik A, García-Lastra JM, Aramburu JA, Moreno M. Red Shift in Optical Excitations on Layered Copper Perovskites under Pressure: Role of the Orthorhombic Instability. Chemistry 2023; 29:e202202933. [PMID: 36322429 PMCID: PMC10107362 DOI: 10.1002/chem.202202933] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Indexed: 11/06/2022]
Abstract
The red shift under pressure in optical transitions of layered compounds with CuCl6 4- units is explored through first-principles calculations and the analysis of available experimental data. The results on Cu2+ -doped (C2 H5 NH3 )2 CdCl4 , that is taken as a guide, show the existence of a highly anisotropic response to pressure related to a structural instability, driven by a negative force constant, that leads to an orthorhombic geometry of CuCl6 4- units but with a hole displaying a dominant 3z2 -r2 character (z being the direction perpendicular to the layer plane). As a result of such an instability, a pressure of only 3 GPa reduces by 0.21 Å the longest Cu2+ -Cl- distance, lying in the layer plane, while leaving unmodified the two other metal-ligand distances. Owing to this fact, it is shown that the lowest d-d transition would experience a red shift of 0.34 eV while the first allowed charge transfer transition is also found to be red shifted but only by 0.11 eV that reasonably concurs with the experimental value. The parallel study on Jahn-Teller systems CdCl2 :Cu2+ and NaCl:Cu2+ involving tetragonal elongated CuCl6 4- units shows that the reduction of the long axis by a pressure of 3 GPa is three times smaller than that for the layered (C2 H5 NH3 )2 CdCl4 :Cu2+ compound. Accordingly, the optical transitions of such systems, which involve a positive force constant, are much less sensitive to pressure than in layered compounds. The origin of the red shift under pressure undergone by the lowest d-d and charge transfer transitions of (C2 H5 NH3 )2 CdCl4 :Cu2+ is discussed in detail.
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Affiliation(s)
- David Carrasco-Busturia
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej. Building 301, 2800 Kgs., Lyngby, Denmark
| | - Inés Sánchez-Movellán
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005, Santander, Spain
| | - Alexander Sougaard Tygesen
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej. Building 301, 2800 Kgs., Lyngby, Denmark
| | - Arghya Bhowmik
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej. Building 301, 2800 Kgs., Lyngby, Denmark
| | - Juan María García-Lastra
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej. Building 301, 2800 Kgs., Lyngby, Denmark
| | - José Antonio Aramburu
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005, Santander, Spain
| | - Miguel Moreno
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005, Santander, Spain
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4
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Sánchez‐Movellán I, Carrasco‐Busturia D, García‐Lastra JM, García‐Fernández P, Aramburu JA, Moreno M. Pressure Effects on 3d
n
(n=4, 9) Insulating Compounds: Long Axis Switch in Na
3
MnF
6
not Due to the Jahn‐Teller Effect. Chemistry 2022; 28:e202200948. [PMID: 35638136 PMCID: PMC9401062 DOI: 10.1002/chem.202200948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Indexed: 11/29/2022]
Abstract
The pressure‐induced switch of the long axis of MnF63− units in the monoclinic Na3MnF6 compound and Mn3+‐doped Na3FeF6 is explored with the help of first principles calculations. Although the switch phenomenon is usually related to the Jahn‐Teller effect, we show that, due to symmetry reasons, it cannot take place in 3dn (n=4, 9) systems displaying a static Jahn‐Teller effect. By contrast, we prove that in Na3MnF6 the switch arises from the anisotropic response of the low symmetry lattice to hydrostatic pressure. Indeed, while the long axis of a MnF63− unit at ambient pressure corresponds to the Mn3+−F3− direction, close to the crystal c axis, at 2.79 GPa the c axis is reduced by 0.29 Å while b is unmodified. This fact is shown to force a change of the HOMO wavefunction favoring that the long axis becomes the Mn3+−F2− direction, not far from crystal b axis, after the subsequent relaxation process. The origin of the different d‐d transitions observed for Na3MnF6 and CrF2 at ambient pressure is also discussed together with changes induced by pressure in Na3MnF6. The present work opens a window for understanding the pressure effects upon low symmetry insulating compounds containing d4 or d9 ions.
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Affiliation(s)
- Inés Sánchez‐Movellán
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada Universidad de Cantabria Avenida de los Castros s/n 39005 Santander Spain
| | - David Carrasco‐Busturia
- Department of Energy Conversion and Storage Technical University of Denmark Anker Engelunds Vej. Building 301 2800 Kgs. Lyngby Denmark
| | - Juan M. García‐Lastra
- Department of Energy Conversion and Storage Technical University of Denmark Anker Engelunds Vej. Building 301 2800 Kgs. Lyngby Denmark
| | - Pablo García‐Fernández
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada Universidad de Cantabria Avenida de los Castros s/n 39005 Santander Spain
| | - José A. Aramburu
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada Universidad de Cantabria Avenida de los Castros s/n 39005 Santander Spain
| | - Miguel Moreno
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada Universidad de Cantabria Avenida de los Castros s/n 39005 Santander Spain
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5
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Sánchez‐Movellán I, Moreno‐Ceballos J, García‐Fernández P, Aramburu JA, Moreno M. New Ideas for Understanding the Structure and Magnetism in AgF 2 : Prediction of Ferroelasticity. Chemistry 2021; 27:13582-13590. [PMID: 34297859 PMCID: PMC8518918 DOI: 10.1002/chem.202101865] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Indexed: 11/25/2022]
Abstract
In the search for new high-temperature superconductors, it has been proposed that there are strong similarities between the fluoroargentate AgF2 and the cuprate La2 CuO4 . We explored the origin of the possible layered structure of AgF2 by studying its parent high-symmetry phase and comparing these results with those of a seemingly analogous cuprate, CuF2 . Our findings first stress the large differences between CuF2 and AgF2 . Indeed, the parent structure of AgF2 is found to be cubic, naturally devoid of any layering, even though Ag2+ ions occupy trigonal sites that, nevertheless, allow the existence of a Jahn-Teller effect. The observed Pbca orthorhombic phase is found when the system is cooperatively distorted by a local E⊗e trigonal Jahn-Teller effect around the silver sites that creates both geometrical and magnetic layering. While the distortion implies that two Ag2+ -F- bonds increase their distance by 15 % and become softer, our simulations indicate that covalent bonding and interlayer electron hopping is strong, unlike the situation in cuprate superconductors, and that, in fact, exfoliation of individual planes might be a harder task than previously suggested. As a salient feature, these results prove that the actual magnetic structure in AgF2 is a direct consequence of vibronic contributions involved in the Jahn-Teller effect. Finally, our findings show that, due to the multiple minima intrinsic to the Jahn-Teller energy surface, the system is ferroelastic, a property that is strongly coupled to magnetism in this argentate.
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Affiliation(s)
- Inés Sánchez‐Movellán
- Departamento de Ciencias de la Tierra yFísica de la Materia CondensadaUniversidad de CantabriaAvenida de los Castros s/n39005SantanderSpain
| | - Jorge Moreno‐Ceballos
- Departamento de Ciencias de la Tierra yFísica de la Materia CondensadaUniversidad de CantabriaAvenida de los Castros s/n39005SantanderSpain
| | - Pablo García‐Fernández
- Departamento de Ciencias de la Tierra yFísica de la Materia CondensadaUniversidad de CantabriaAvenida de los Castros s/n39005SantanderSpain
| | - Jose Antonio Aramburu
- Departamento de Ciencias de la Tierra yFísica de la Materia CondensadaUniversidad de CantabriaAvenida de los Castros s/n39005SantanderSpain
| | - Miguel Moreno
- Departamento de Ciencias de la Tierra yFísica de la Materia CondensadaUniversidad de CantabriaAvenida de los Castros s/n39005SantanderSpain
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6
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Aramburu JA, Moreno M. Key Role of Deep Orbitals in the d x2-y2-d 3z2-r2 Gap in Tetragonal Complexes and 10 Dq. J Phys Chem A 2021; 125:2284-2293. [PMID: 33724839 PMCID: PMC8459450 DOI: 10.1021/acs.jpca.0c11609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Using first-principles calculations,
we show that the origin of
the intrinsic a1g(∼3z2 – r2)–b1g(∼x2 – y2) splitting,
Δint, in tetragonal transition-metal complexes and
the variations of the cubic field splitting, 10Dq, with the metal–ligand distance, R, are
much more subtle than commonly thought. As a main novelty, the key
role played by covalent bonding with deep valence ligand levels and
thus the inadequacy of too simple models often used for the present
goal is stressed. Taking as a guide the isolated D4h CuF64– complex, it is proved that
Δint essentially arises from bonding with deep 2s(F)
orbitals despite them lying ∼23 eV below 2p(F) orbitals. This
conclusion, although surprising, is also supported by results on octahedral
fluoride complexes where the contribution to 10Dq splitting from bonding with 2s(F) orbitals is behind its strong R dependence, stressing that explanations based on the crystal-field
approach are simply meaningless.
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Affiliation(s)
- J A Aramburu
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain
| | - M Moreno
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain
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7
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Bersuker IB. Jahn–Teller and Pseudo-Jahn–Teller Effects: From Particular Features to General Tools in Exploring Molecular and Solid State Properties. Chem Rev 2020; 121:1463-1512. [DOI: 10.1021/acs.chemrev.0c00718] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Isaac B. Bersuker
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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8
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Aramburu JA, Moreno M. Ground State and Optical Excitations in Compounds with Tetragonal CuF 64- Units: Insight into KAlCuF 6 and CuFAsF 6. Inorg Chem 2020; 59:539-547. [PMID: 31820942 DOI: 10.1021/acs.inorgchem.9b02827] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
It has been argued that AAlCuF6 (A = K, Cs) and CuFAsF6 are the only known crystals that exhibit compressed CuF64- units due to the Jahn-Teller effect. However, no grounds for this singular behavior have yet been reported. By means of first-principles calculations on such compounds and the isomorphous compounds involving Zn2+ ions instead of Cu2+, we prove that neither the ground state nor the equilibrium geometry of CuF64- complexes in KAlCuF6 and CuFAsF6 is the result of a Jahn-Teller effect. In contrast, it is shown that the internal electric field, ER(r), created by the rest of the lattice ions upon the localized electrons in the complex, plays an important role in understanding this matter as well as the d-d transitions of these two compounds. The energy of an optical transition is shown to involve two contributions: the intrinsic contribution derived for the isolated CuF64- unit at equilibrium and the extrinsic contribution coming from the ER(r) field. Aside from reproduction of the experimental d-d transitions observed for KAlCuF6, it is found that in CuFAsF6 the b1g(x2 - y2) → a1g(3z2 - r2) transition is not the lowest one due to the stronger effects from the internal field. Interestingly, the intrinsic contribution corresponding to that transition can simply be written as β(Req - Rax) where Req and Rax are the equatorial and axial Cu2+-F- distances and β = 2.7 eV/Å is the same for all systems involving tetragonal CuF64- units and an average metal-ligand distance close to 2.03 Å. This shows the existence of a common point shared by the Jahn-Teller system KZnF3:Cu2+ and other non-Jahn-Teller systems such as KAlCuF6, CuFAsF6, K2ZnF4:Cu2+, and Ba2ZnF6:Cu2+. Although most Jahn-Teller systems display an elongated geometry, there are however many Cu2+ compounds with a compressed geometry but hidden by an additional orthorhombic instability. The lack of that instability in KAlCuF6 and CuFAsF6 is also discussed.
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Affiliation(s)
- Jose Antonio Aramburu
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada , Universidad de Cantabria , Avenida de los Castros s/n , 39005 Santander , Spain
| | - Miguel Moreno
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada , Universidad de Cantabria , Avenida de los Castros s/n , 39005 Santander , Spain
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9
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Sanchez-Movellan I, Aramburu JA, Moreno M. Local structure and excitations in systems with CuF 64− units: lack of Jahn–Teller effect in the low symmetry compound Na 2CuF 4. Phys Chem Chem Phys 2020; 22:7875-7887. [DOI: 10.1039/c9cp06843k] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The lack of a Jahn–Teller effect in Na2CuF4 is illustrated by the anisotropy of the Na2ZnF4 parent lattice.
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Affiliation(s)
- I. Sanchez-Movellan
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada
- Universidad de Cantabria
- 39005 Santander
- Spain
| | - J. A. Aramburu
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada
- Universidad de Cantabria
- 39005 Santander
- Spain
| | - M. Moreno
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada
- Universidad de Cantabria
- 39005 Santander
- Spain
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10
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Aramburu JA, Moreno M. Explaining the optical spectrum of CrF 2 and CuF 2 model materials: role of the tetragonal to monoclinic instability. Phys Chem Chem Phys 2019; 21:11714-11723. [PMID: 31134257 DOI: 10.1039/c9cp01822k] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The properties of MF2 (M = Cr, Cu) model compounds are usually interpreted assuming a Jahn-Teller effect leading to elongated MF64- units. By means of the analysis of experimental data and first-principles calculations on both the monoclinic P21/c structure and the parent rutile structure (tetragonal P42/mnm space group), we prove that such an assumption is not correct. It is shown that in MF2 compounds, the MF64- complexes are actually compressed in the parent phase but along a different direction, a situation that is however hidden by an additional orthorhombic instability due to a negative force constant of b2g and b3g modes of the cell. This distortion plays a key role in understanding the high experimental value of the lowest d-d transition energy, E1 = 1.23 and 0.93 eV for CrF2 and CuF2, respectively, when compared to the value E1 = 0.40 eV derived for the Jahn-Teller system of KZnF3:Cu2+. Aside from reproducing reasonably the experimental values of spin allowed d-d transitions of both compounds, our first-principles calculations show the existence of an accidental degeneracy involving the yz and xy levels in the final P21/c structure. Moreover, the internal electric field of CrF2 and CuF2 is found to be much less anisotropic than in layered compounds like K2CuF4 and thus it has little influence on the d-d transition energy. The influence of the (3z2 - r2) - (x2 - y2) hybridization, caused by the orthorhombic distortion, on the electronic density and the magnetic coupling between layers is also briefly discussed. The present results stress that the interpretation of experimental data using simple parameterized models can lead to wrong conclusions.
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Affiliation(s)
- J A Aramburu
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005 Santander, Spain.
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11
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Aramburu JA, Moreno M. Understanding the Structure and Ground State of the Prototype CuF 2 Compound Not Due to the Jahn-Teller Effect. Inorg Chem 2019; 58:4609-4618. [PMID: 30888161 DOI: 10.1021/acs.inorgchem.9b00178] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Insulating CuF2 is considered a prototype compound displaying a Jahn-Teller effect (JTE) which gives rise to elongated CuF64- units. By means of first-principles calculations together with an analysis of experimental data of both CuF2 and Cu2+-doped ZnF2, we demonstrate that such an idea is not correct. For ZnF2:Cu2+, we find that CuF64- units are compressed always along the Z local axis with a hole essentially in a 3 z2- r2 antibonding orbital, in agreement with experimental EPR data that already underline the absence of a JTE. The structure of the monoclinic CuF2 crystal also comes from compressed CuF64- complexes, although hidden by an additional orthorhombic instability due to a negative force constant of b2g and b3g local modes. The associated distortion, similar to that involved in K2CuF4 and other layered Cu2+ compounds, is also shown to be developed for ZnF2:Cu2+ upon increasing the copper concentration. The origin of this cooperative effect is discussed together with the differences between non-Jahn-Teller systems like ZnF2:Cu2+ and CuF2 and true Jahn-Teller systems like KZnF3:Cu2+. From present results and those on layered compounds, the usual assumption of a JTE for explaining the properties of d9 ions in low-symmetry lattices can hardly be right.
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Affiliation(s)
- José Antonio Aramburu
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada , Universidad de Cantabria , Avenida de los Castros s/n , 39005 Santander , Spain
| | - Miguel Moreno
- Departamento de Ciencias de la Tierra y Física de la Materia Condensada , Universidad de Cantabria , Avenida de los Castros s/n , 39005 Santander , Spain
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12
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Kurzydłowski D, Derzsi M, Mazej Z, Grochala W. Crystal, electronic, and magnetic structures of M2AgF4 (M = Na–Cs) phases as viewed from the DFT+U method. Dalton Trans 2016; 45:16255-16261. [DOI: 10.1039/c6dt03125k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Theoretical analysis of various polymorphic forms of a series of four alkali metal fluoroargentates(ii), M2AgF4 (M = Na–Cs), helped to establish clear trends of crystal structures and magnetic properties across the alkali metal series.
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Affiliation(s)
- Dominik Kurzydłowski
- Centre of New Technologies
- University of Warsaw
- Warsaw
- Poland
- Faculty of Mathematics and Natural Sciences
| | - Mariana Derzsi
- Centre of New Technologies
- University of Warsaw
- Warsaw
- Poland
| | - Zoran Mazej
- Department of Inorganic Chemistry and Technology
- Jožef Stefan Institute
- SI-1000 Ljubljana
- Slovenia
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