Strong-correlation effects in Born effective charges

Filippetti, Alessio; Spaldin, Nicola A.

doi:10.1103/physrevb.68.045111

Cited by 65 publications

(48 citation statements)

References 58 publications

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“…7 middle panel). We rationalize this behavior as follows: it is established that the stabilization of polar distortions in the d 3 perovskite manganites arises from the charge transfer from filled oxygen 2p to empty manganese 3d e g orbitals [30,50] by analogy to the hybridization with the empty Ti 3d t 2g orbitals in the prototypical d 0 perovskite oxides such as BaTiO 3 . [51] When an oxygen vacancy is formed, the two charge compensating electrons occupy the manganese e g orbitals, [18] inhibiting the formation of partial covalent bonds between Mn 3d e g and O 2p.…”

Section: Oxygen-vacancy Stability and Orderingmentioning

confidence: 89%

Coupling and competition between ferroelectricity, magnetism, strain, and oxygen vacancies in AMnO3 perovskites

et al. 2016

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We use first-principles calculations based on density functional theory to investigate the interplay between oxygen vacancies, A-site cation size/tolerance factor, epitaxial strain, ferroelectricity, and magnetism in the perovskite manganite series, AMnO 3 (A = Ca 2+ , Sr). We find that, as expected, increasing the volume through either chemical pressure or tensile strain generally lowers the formation energy of neutral oxygen vacancies consistent with their established tendency to expand the lattice. Increased volume also favors polar distortions, both because competing rotations of the oxygen octahedra are suppressed and because Coulomb repulsion associated with cation off-centering is reduced. Interestingly, the presence of ferroelectric polarization favors ferromagnetic (FM) over antiferromagnetic (AFM) ordering due to suppressed AFM superexchange as the polar distortion bends the Mn-O-Mn bond angles away from the optimal 180°. Intriguingly, we find that polar distortions compete with the formation of oxygen vacancies, which have a higher formation energy in the polar phases; conversely the presence of oxygen vacancies suppresses the onset of polarization. In contrast, oxygen vacancy formation energies are lower for FM than AFM orderings of the same structure type. Our findings suggest a rich and complex phase diagram, in which defect chemistry, polarization, structure, and magnetism can be modified using chemical potential, stress or pressure, and electric or magnetic fields.

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Section: Oxygen-vacancy Stability and Orderingmentioning

confidence: 89%

Coupling and competition between ferroelectricity, magnetism, strain, and oxygen vacancies in AMnO3 perovskites

et al. 2016

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“…The SIESTA 40 package, implemented over a local (atomic) orbital basis set and norm-conserving pseudopotentials, was employed for LDA (LDA-LO below) and ASIC calculations (note that ASIC is available only in a developer version of the code). The variational PSIC/ASIC 31 approach evolves from the nonvariational precursors PSIC 37,42 and ASIC. 43 The new method describes electronic properties as accurately as its precursors and variationality allows for its application to structural optimization and frozen-phonon calculations via quantum forces.…”

Section: Methodsmentioning

confidence: 99%

“…42. The VASP 41 code, employing the projected augmented wave (PAW) approach, is used for PBE 33 and HSE 30 calculations.…”

Section: Methodsmentioning

confidence: 99%

Exchange interactions and magnetic phases of transition metal oxides: Benchmarking advancedab initiomethods

et al. 2011

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The magnetic properties of the transition metal monoxides MnO and NiO are investigated at equilibrium and under pressure via several advanced first-principles methods coupled with Heisenberg Hamiltonian Monte Carlo. The comparative first-principles analysis involves two promising beyond-local density functionals approaches, namely the hybrid density functional theory and the recently developed variational pseudo-self-interaction correction method, implemented with both plane-wave and atomic-orbital basis sets. The advanced functionals deliver a very satisfying rendition, curing the main drawbacks of the local functionals and improving over many other previous theoretical predictions. Furthermore, and most importantly, they convincingly demonstrate a degree of internal consistency, despite differences emerging due to methodological details (e.g., plane waves versus atomic orbitals).

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“…the polarization derivative with respect to atomic displacement [13]. A loss of effective polarizability will to decrease the ionic dielectric activity.…”

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confidence: 99%

Dielectric constant boost in amorphous sesquioxides

Delugas

Fiorentini

Filippetti

2008

Applied Physics Letters

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High-κ dielectrics for insulating layers are a current key ingredient of microelectronics. X2O3 sesquioxide compounds are among the candidates. Here we show for a typical material of this class, Sc2O3, that the relatively modest dielectric constant of its crystalline phase is enhanced in the amorphous phase by over 40 % (from ∼15 to ∼22). This is due to the disorder-induced activation of low frequency cation-related modes which are inactive or inefficient in the crystal, and by the conservation of effective dynamical charges (a measure of atomic polarizability). The analysis employs density-functional energy-force and perturbation-theory calculations of the dielectric response of amorphous samples generated by pair-potential molecular dynamics.PACS numbers: 77. 22-d,63.20-e,78.30-j,61.66-f High-dielectric constant ("high-κ") materials are gradually replacing silica [1] as gate dielectrics in integrated electronics. Policrystalline layers thereof usually behave badly in electrical terms due to grain-boundary conduction, so that amorphous layers are seriously studied as well. Whether or not the κ of the crystal will be conserved upon amorphization is not obvious a priori [2], and should be assessed during the validation of a candidate dielectric to be used in thin insulating coatings.Considerable attention has been devoted recently [3, 4] to sesquioxides X 2 O 3 with the trivalent cation X=Y, Sc, or a rare-earth atom. Almost all these materials adopt the cubic bixbyite crystal structure. Experiments [3,4] and theory [4,5] largely agree that their static dielectric constant in that phase is in the order of 12 to 15, and of vibrational origin for about ∼60-70%. The microscopic rationale for this behavior was given recently by the present authors [4,5]: the infra-red (IR) active vibrational modes are relatively high-frequency and essentially cation-independent motions.As we discussed in detail elsewhere [2,6,7,8], the dielectric constant κ s =κ ∞ +κ ion in high-κ materials is generally dominated by the lattice-vibrational component κ ion , a factor 2 to 10 larger than the electronic κ ∞ . By its definition(with z the mode charge vector, Ω the system volume, Z * i,α,β the effective or dynamical or Born charge tensor and M i the mass of atom i, ξ i,λβ and ω the eigenvector and eigenfrequency of mode λ at zero wave-vector, and α, β cartesian indexes), a large κ ion is due to large effective polarizabilities as measured by dynamical charges, termed "anomalous" if they exceed nominal ionicity, and to soft IR vibrational modes. A question that naturally arises is, will amorphization, i.e. microscopic disorder, deteriorate the dielectric constant of these oxides ? In this Letter we show, based on ab initio calculations, that scandia, Sc 2 O 3 , has a larger dielectric constant in its amorphous phase than in its crystal phase. This dielectric constant boost is due to a) hardly any loss in dynamical polarizability, and b) disorder-induced IR activation of non-polar low-energy modes related to cation-oxygen combined motions...

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Strong-correlation effects in Born effective charges

Cited by 65 publications

References 58 publications

Coupling and competition between ferroelectricity, magnetism, strain, and oxygen vacancies in AMnO3 perovskites

Coupling and competition between ferroelectricity, magnetism, strain, and oxygen vacancies in AMnO3 perovskites

Exchange interactions and magnetic phases of transition metal oxides: Benchmarking advancedab initiomethods

Dielectric constant boost in amorphous sesquioxides

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