Molecular orbital analysis of oxygen vacancy in YBa2Cu3O7−δ

Rocha, Judith Advíncula; Pavão, Antonio C.

doi:10.1016/j.physc.2004.07.007

Cited by 4 publications

(4 citation statements)

References 17 publications

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“…The HOMO-LUMO gap is not the superconducting gap, which is defined as the lowest energy gap originated from the electron-electron interaction of the Cooper pair and is responsible for the main characteristics of the superconducting state [22][23][24][25][26]. However, a comparative analysis of the HOMO-LUMO gap can be useful to correlate the superconductor state with the atoms involved in the electron transfer [4].…”

Section: Resultsmentioning

confidence: 99%

“…The effective core potential using the minimum base set LANL1MB of Hay and Wadt [21] was used for all atoms. We have considered the fcc unit cell of K 3 C 60 as our cluster model (K 21 (C 60 ) 14 , see Figure 1, but different clusters are also analyzed: K 38 (C 60 ) 23 , K 17 (C 60 ) 9 , K 17 (C 60 ) 5 , K 9 (C 60 ) 4 , K 9 (C 60 ) 7 , K 13 (C 60 ) 4 , and K 13 (C 60 ) 5 . Clusters are composed of large numbers of atoms, the largest cluster K 38 (C 60 ) 23 has 1,418 atoms, but their high symmetry allowed calculations to be performed with relatively low computational demand.…”

Section: Computational Detailsmentioning

confidence: 99%

“…ollowing our previous studies on the superconductivity in YBCO [1][2][3][4], we now present a K 3 C 60 superconductivity analysis within the framework of the resonating valence-bond (RVB) theory, a theory of the electronic structure of metals, developed 60 years ago by Pauling [5][6][7][8], which provides the basis for a detailed description of the electron-phonon interaction in relation to the atomic numbers of the elements and the composition of superconductors. The RVB theory successfully explains a number of superconductor properties; it is consistent with Bardeen-Cooper-Schrieffer (BCS) theory [9], and it is directly connected to chemical properties that may be calculated by quantum chemical methods.…”

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confidence: 99%

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Resonating valence‐bond mechanism for the superconductivity in K₃C₆₀

Bastos

Costa

Pavão

2010

Int J of Quantum Chemistry

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Density functional theory calculations in different cluster models, the largest one K 38 (C 60 ) 23 with 1,418 atoms, combined with the resonating valence-bond theory show that superconductivity in K 3 C 60 involves interaction of C 60 with K þ , K 0 , and K À in octahedral interstices as well as immobilization of negative charges on positive tetrahedral K atoms. We found that the orbitals involved in the highest occupied molecular orbital-lowest unoccupied molecular orbital gap are mainly from C 60 and octahedral potassium atoms. We suggest that a K 3 C 60 superconductor improvement can be achieved through potassium atom vacancy in octahedral sites.

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Section: Resultsmentioning

confidence: 99%

Section: Computational Detailsmentioning

confidence: 99%

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confidence: 99%

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Resonating valence‐bond mechanism for the superconductivity in K₃C₆₀

Bastos

Costa

Pavão

2010

Int J of Quantum Chemistry

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“…Т с is known to depend on the concentration of mobile oxygen distributed in the chain Сu(1)O 1-δ planes and may reach the highest level (~92 K) at δ = 0÷0.2 [8]. This correlation is however not definitive since Т с may vary at a constant δ due to the effect of not only the concentration of oxygen vacancies but also their ordering in the anionic sublattice of YBa 2 Cu 3 O 7-δ crystals [9][10][11][12][13][14]. The order parameter of oxygen vacancies (ηv 0 ) is in turn controlled by temperature and annealing time and therefore affects Т с [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Electrical conductivity of YBa2Cu3O7-δ single crystals under conditions of anionic ordering in Cu(1)O1-δ layers

Каланда¹

2020

MoEM

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The influence of thermocycling annealing processes on the oxygen ordering degree (order parameter) in YBa2Cu3O7-δ single crystals has been studied. It has been shown that an increase in the critical onset temperature of the transition to the superconducting state during thermocycling annealing procedures is consistent with the decrease of the σс/σаb parameter. This fact indicates a redistribution of the electronic density between the structurally inhomogeneous Cu(2)O2 and Cu(1)O1-δ planes, due to the formation of oxygen long-range order in the O(4)–Cu(1)–O(4) linear groups along the (b) crystal structure axis of the unit cell, and elimination of oxygen defects in the square nets of the Cu(2)O2 planes. The existence of the critical value of the conductivity anisotropy σс/σаb, below which its behavior does not correlate with the change of Тс, has been confirmed. In this case an increase in Тс and orthorhombic distortion of the crystal structure during isothermal annealing are caused by the amplification of the “interlayer” interaction between the Cu(2)О2 and Cu(1)О1-δ planes. As a result, the contribution of the Cu(1)О1-δ chain layers to the electron state density at the Fermi level increases. These layers can acquire superconducting properties due to tunneling of Cooper pairs from the Cu(2)О2 planes resulting in the formation of the induced superconductivity in these planes.

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