Cation Ordering in LaBa₂Cu₂TaO_8+y

Abstract

LaBa2Cu2TaO8+y crystallizes in a tetragonal unit cell with the dimensions a=3.9674(2) and c=12.052(1) Å, showing semiconductivity. In this compound, the Ta ions were found to preferentially occupy the Cu1 site between the two Ba layers in the LaBa2Cu3O7-y -type structure.

Predicted properties ofNd1.5Ce0.5Sr2Blackstead1, Dow2 1998Phys. Rev. B16120View full textAdd to dashboardCite

“…͑They obtained NbO 2 layers.͒ The expectation, based on a cuprate-plane picture of superconductivity, was that R122M -8 would superconduct, but it did not ͑for either M ϭNb or M ϭTa). 6,101,102 It appears to us that the reason the R122Nb-8 compounds were expected to superconduct with higher critical temperatures than R123-7 was that Nb was perhaps expected to display a charge-state of ϩ3, rather than ϩ5. Our analyses of the bond-lengths in these compounds in terms of bondvalence-sum charges, indicate that the Nb charge-state is invariably ϩ5.…”

An X-ray Powder Diffraction Study of Sr2LnTaCu2O8, Ln = Nd, Sm, Eu, Gd

“…3.1. XRD characterization of the samples X-ray powder diffractograms indicated that the prepared samples Sr2NdTaCu2Os, Sr2SmTaCu2Os, Sr2EuTaCu208 and SrzGdTaCuzOs were isostructural with tetragonal BazLaTaCu208 prepared by Murayama et al (1988). The unit-cell parameters were determined using the method proposed by Toraya (1993) by means of the computer program UNITCELL.…”

“…For instance, A1 and Ni tend to occupy site (1) while Zn prefers site (2) (Jones et al, 1988). A complete replacement of square-planar-coordinated Cu ions by octahedrally coordinated Ta ions has been reported for © 1996 International Union of Crystallography Printed in Great Britain -all rights reserved the semiconducting tetragonal Ba2LaTaCu2Os (Murayama et al, 1988), while recent crystal structure determinations of Sr2YMCu207, M=Co, Ga have revealed a complete replacement of square-planar coordinated Cu by tetrahedrally coordinated Co or Ga ions (Huang, Cava, Santoro, Krajewski & Peck, 1992). The present paper reports the preparation of semiconducting oxides Sr2LnTaCu2Os, Ln=Nd, Sm, Eu, Gd, their X-ray powder diffraction characterization and the structure refinement of Sr2SmTaCu208 from X-ray powder diffraction data, as a part of our investigation of the quaternary oxide systems with possible superconducting properties (Bmi~evi6 et al, 1993).…”

Subsolidus phase relations of the SrO–Ta2O5–CuO system at 900°C in air

“…In relation to superconductivity, it is interesting to note that the phases of the TaM 2 RECu 2 O 8−ı (M = Sr, Ba; RE = Pr, Nd, Sm, Eu, Gd) series crystallize in a structure type similar to that of the high-temperature superconductor (HTS) YBa 2 Cu 3 O 7−ı , where Ta 5+ ions are accommodated in the basal plane, whereas the double CuO 2 pyramidal planes are maintained [50][51][52][53]. TaSr 2 (NdCe) 2 Cu 2 O y is the Ta analog of the phase TlBa 2 NdCeCu 2 O 9 [54] and Pb 2 Sr 2 Cu 2 TaO 8 Cl crystallizes in a layered tetragonal structure reminiscent of that of HTS materials [55].…”