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8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on La2CuO4 by Materials Project

La2CuO4 is (La,Ba)CuO4 structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. La3+ is bonded in a 1-coordinate geometry to nine O2- atoms. There are a spread of La–O bond distances ranging from 2.31–2.77 Å. Cu2+ is bonded to six O2- atoms to form corner-sharing CuO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (1.91 Å) and two longer (2.46 Å) Cu–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 6-coordinate geometry to five equivalent La3+ and one Cu2+ atom. In the second O2- site, O2- is bonded to four equivalent La3+ and two equivalent Cu2+ atoms to form a mixture of distorted corner, edge, and face-sharing OLa4Cu2 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La2CuO4 by Materials Project

La2CuO4 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. La3+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.37 Å) and four longer (2.76 Å) La–O bond lengths. Cu2+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Cu–O bond lengths are 2.00 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent La3+ atoms to form OLa4 tetrahedra that share corners with twelve equivalent OLa4Cu2 octahedra, corners with four equivalent OLa4 tetrahedra, edges with two equivalent OLa4Cu2 octahedra, and edges with four equivalent OLa4 tetrahedra. The corner-sharing octahedra tilt angles range from 11–68°. In the second O2- site, O2- is bonded to four equivalent La3+ and two equivalent Cu2+ atoms to form distorted OLa4Cu2 octahedra that share corners with two equivalent OLa4Cu2 octahedra, corners with twelve equivalent OLa4 tetrahedra, edges with two equivalent OLa4Cu2 octahedra, edges with two equivalent OLa4 tetrahedra, and faces with four equivalent OLa4Cu2 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La2CuO4 by Materials Project

La2CuO4 is (La,Ba)CuO4-like structured and crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. La3+ is bonded in a 1-coordinate geometry to nine O2- atoms. There are a spread of La–O bond distances ranging from 2.31–2.87 Å. Cu2+ is bonded to six O2- atoms to form corner-sharing CuO6 octahedra. The corner-sharing octahedral tilt angles are 1°. There are four shorter (1.91 Å) and two longer (2.44 Å) Cu–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 6-coordinate geometry to five equivalent La3+ and one Cu2+ atom. In the second O2- site, O2- is bonded to four equivalent La3+ and two equivalent Cu2+ atoms to form a mixture of distorted corner, edge, and face-sharing OLa4Cu2 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Electron energy spectrum and magnetic interactions in high-T(sub c) superconductors

The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T sub N1 and T sub N2. The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T sub N2 reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T sub N1 and T sub N2 depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J sub ij parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors.

Turshevski, S. A.↗
NASA NTRS1991

Electron energy spectrum and magnetic interactions in high-Tc superconductors

The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T(sub N1) and T(sub N2). The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T(sub N2) reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T(sub N1) and T(sub N2) which depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg Hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J(sub ij) parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors.

Turshevski, S. A.↗
NASA NTRS1990

Study of local structure and magnetism in high-T(sub c) copper oxide superconductors

The muon spin rotation (MUSR) study of local magnetism of Sr-doped La2CuO4 is reviewed. Emphasis is placed on magnetic order as detected by local and bulk probes with local atomic environments studied by x ray absorption fine structure (XAFS). Correlations between the MUSR study of local magnetic ordering and the bulk magnetization study are presented along with a discussion of the dependence upon oxygen stoichiometry. Results are presented for both superconducting phases and magnetic phases. Recent data which reveals the existence of local magnetic ordering in the hydrogen-doped YBa2Cu3O7 system are also discussed.

Budnick, J. I.↗
NASA NTRS1991

The electronic Hamiltonian for cuprates

A realistic many-body Hamiltonian for the cuprate superconductors should include both copper d and oxygen p states, hopping matrix elements between them, and Coulomb energies, both on-site and inter-site. We have developed a novel computational scheme for deriving the relevant parameters ab initio from a constrained occupation local density functional. The scheme includes numerical calculation of appropriate Wannier functions for the copper and oxygen states. Explicit parameter values are given for La2CuO4. These parameters are generally consistent with other estimates and with the observed superexchange energy. Secondly, we address whether this complicated multi-band Hamiltonian can be reduced to a simpler one with fewer basis states per unit cell. We propose a mapping onto a new two-band effective Hamiltonian with one copper d and one oxygen p derived state per unit cell. This mapping takes into account the large oxygen-oxygen hopping given by the ab initio calculations.

Annett, James F.↗