Spin localization, magnetic ordering, and electronic properties of strongly correlated 
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 sesquioxides (Ln=La, Ce, Pr, Nd)

El-Kelany, Kh. E.; Ravoux, Corentin; Desmarais, Jacques K.; Cortona, Pietro; Pan, Yuanming; Tse, John S.; Erba, Alessandro

doi:10.1103/physrevb.97.245118

Cited by 44 publications

(47 citation statements)

References 65 publications

(93 reference statements)

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“…At variance with ZIF-8, ZIF-67 is a spin-polarized system where each Co center hosts three unpaired electrons in its partially occupied d orbitals, and thus requires some special care in order to be accurately described. 34 Three dis- minority electron densities) of the three magnetic configurations. The broken-symmetry fully antiferromagnetic configuration is the most stable one (relative stabilities of different magnetic configurations are given in Figure 3).…”

Section: Resultsmentioning

confidence: 99%

Pressure-driven mechanical anisotropy and destabilization in zeolitic imidazolate frameworks

et al. 2019

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The anisotropic mechanical response of ZIF-8 and ZIF-67 is investigated as a function of pressure and its main features (including shear-destabilization eventually leading to amorphization) discussed in terms of specific lattice vibrations and structural changes occurring in the framework. At zero pressure, the two ZIFs are characterized by an elastic anisotropy with directions of maximum and minimum stiffness along 111 and 100 , respectively. At P = 0.2 GPa, the framework exhibits a perfectly isotropic mechanical response while at P > 0.2 GPa a different (complementary) anisotropic response is observed with directions of maximum and minimum stiffness along 100 and 111 , respectively. The bulk modulus of the two ZIFs initially slightly increases up to 0.1 GPa of pressure and then decreases at higher pressures. Amorphization in both ZIF-8 and ZIF-67 is confirmed to be due to the pressure-driven mechanical instability of their frameworks to shear deformations. The directional elastic moduli of the two ZIFs are partitioned into contributions from specific normal modes of vibration. The elastic constants C11, and C12 (and thus the bulk modulus K = 1/3(C11 + 2C12)) are mostly affected by symmetric "gate-opening" vibrations of the imidazolate linkers in the four-membered rings. The C44 shear elastic constant (and thus the mechanical instability and amorphization of the framework) are instead related to asymmetric "gate-opening" vibrations of the four-membered rings.

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Section: Resultsmentioning

confidence: 99%

Pressure-driven mechanical anisotropy and destabilization in zeolitic imidazolate frameworks

et al. 2019

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“…54 In accordance with the previous study on Ln2O3 systems, the oxygen basis set developed by Towler et al was used, with an integration grid consisting of 99 radial points and 1454 angular points. 55 We note that this oxygen basis set was not specifically developed for hyperfine calculations, which need accurate treatment of the core states; more extended oxygen basis sets such as the IGLO-III set were attempted, but resulted in SCF instabilities, presumably arising from the 'mixing' of two basis sets with different qualities.…”

Section: Dftmentioning

confidence: 99%

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

Hope

Halat

Lee

et al. 2019

Solid State Nuclear Magnetic Resonance

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Paramagnetic solid-state NMR of lanthanide (Ln) containing materials can be challenging due to the high electron spin states possible for the Ln f electrons, which result in large paramagnetic shifts, and these difficulties are compounded for 17 O due to the low natural abundance and quadrupolar character. In this work, we present examples of 17 O NMR experiments for lanthanide oxides and strategies to overcome these difficulties. In particular, we record and assign the 17 O NMR spectra of monoclinic Sm2O3 and Eu2O3 for the first time, as well as performing density functional theory (DFT) calculations to gain further insight into the spectra. The temperature dependence of the Sm 3+ and Eu 3+ magnetic susceptibilities are investigated by measuring the 17 O shift of the cubic sesquioxides over a wide temperature range, which reveal non-Curie temperature dependence due to the presence of low-lying electronic states. This behaviour is reproduced by calculating the electron spin as a function of temperature, yielding shifts which agree well with the experimental values. Using the understanding of the magnetic behaviour gained from the sesquioxides, we then explore the local oxygen environments in 15 at% Sm-and Eu-substituted CeO2, with the 17 O NMR spectrum exhibiting signals due to environments with zero, one and two nearest neighbour Ln ions, as well as further splitting due to oxygen vacancies. Finally, we extract an activation energy for oxygen vacancy motion in these systems of 0.35 ± 0.02 eV from the Arrhenius temperature dependence of the 17 O T1 relaxation constants, which is found to be independent of the Ln ion within error. The relation of this activation energy to literature values for oxygen diffusion in Ln-substituted CeO2 is discussed to infer mechanistic information which can be applied to further develop these materials as solid-state oxide-ion conductors. Recent efforts by Heinzmann et al. have shown that 17 O NMR (and T1) measurements can be applied to GDC to quantify doping behaviour and to extract activation energy values that can be ascribed to oxideion motion. 41 However, to our knowledge 17 O NMR and/or relaxometry-based techniques have not been used to study conduction in other Ln-substituted CeO2 materials, likely due to the aforementioned difficulties in interpreting NMR spectra of paramagnetic phases. In this work, we apply the lessons learned regarding the magnetic behaviour of Sm 3+ and Eu 3+ as seen in the paramagnetic 17 O NMR of the monoclinic Ln2O3 polymorphs to guide the analysis of variable-temperature 17 O spectra of Sm-and Eu-substituted CeO2.

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“…The Gd 4f orbitals are described in the valence by three Gaussians (i.e., “(3f)” notation). The Gd effective valence basis set is [5(sp)2d3f] and contains 36 electrons [ 62 , 63 ]. Moreover, the Hf effective valence basis set is [3(sp)2d] and contains 12 electrons [ 64 ].…”

Section: Methodsmentioning

confidence: 99%

Structural Evolution and Magnetic Properties of Gd2Hf2O7 Nanocrystals: Computational and Experimental Investigations

et al. 2020

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Structural evolution in functional materials is a physicochemical phenomenon, which is important from a fundamental study point of view and for its applications in magnetism, catalysis, and nuclear waste immobilization. In this study, we used x-ray diffraction and Raman spectroscopy to examine the Gd2Hf2O7 (GHO) pyrochlore, and we showed that it underwent a thermally induced crystalline phase evolution. Superconducting quantum interference device measurements were carried out on both the weakly ordered pyrochlore and the fully ordered phases. These measurements suggest a weak magnetism for both pyrochlore phases. Spin density calculations showed that the Gd3+ ion has a major contribution to the fully ordered pyrochlore magnetic behavior and its cation antisite. The origin of the Gd magnetism is due to the concomitant shift of its spin-up 4f orbital states above the Fermi energy and its spin-down states below the Fermi energy. This picture is in contrast to the familiar Stoner model used in magnetism. The ordered pyrochlore GHO is antiferromagnetic, whereas its antisite is ferromagnetic. The localization of the Gd-4f orbitals is also indicative of weak magnetism. Chemical bonding was analyzed via overlap population calculations: These analyses indicate that Hf-Gd and Gd-O covalent interactions are destabilizing, and thus, the stabilities of these bonds are due to ionic interactions. Our combined experimental and computational analyses on the technologically important pyrochlore materials provide a basic understanding of their structure, bonding properties, and magnetic behaviors.

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Spin localization, magnetic ordering, and electronic properties of strongly correlated Ln2O3 sesquioxides (Ln=La, Ce, Pr, Nd)

Cited by 44 publications

References 65 publications

Pressure-driven mechanical anisotropy and destabilization in zeolitic imidazolate frameworks

Pressure-driven mechanical anisotropy and destabilization in zeolitic imidazolate frameworks

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

Structural Evolution and Magnetic Properties of Gd2Hf2O7 Nanocrystals: Computational and Experimental Investigations

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