High pressure synthesis of NdCuO{sub 3-{delta}} perovskites (0 {le} {delta} {le} 0.5)
- Columbia Univ., Palisades, NY (United States)
- IBM Thomas J. Watson Research Center, Yorktown Heights, NY (United States)
- Univ. of Caen (France)
Oxygen-deficient perovskites NdCuO{sub 3-{delta}} (0 {le} {delta} {le} 0.5) were prepared for the first time at high pressures in a multianvil apparatus and characterized by X-ray and electron diffraction and by electron microprobe. Several new oxygen vacancy-order phases could be stabilized depending upon {delta} and synthetic conditions. The crystal structures of NdCuO{sub 3-{delta}} are related to those previously observed in the LaCuO{sub 3-{delta}} system, but are more highly distorted due to the smaller Nd cation size, leading to different symmetries, A-site coordination numbers and unit cell dimensions. Electron diffraction shows that NdCuO{sub 2.5} crystallizes in an orthorhombic {radical}2a{sub p} x 2{radical}2a{sub p} x a{sub p} subcell with a 6{radical}2a{sub p} x 4{radical}2a{sub p} x 2a{sub p} supercell, where a{sub p} is the simple cubic perovskite lattice parameter. NdCuO{sub 2.6} crystallizes in a monoclinic {radical}5a{sub p} x {radical}5a{sub p} x 2a{sub p} cell. In addition, two other phases with {radical}10a{sub p} x {radical}10a{sub p} x 2a{sub p} and {radical}5a{sub p} x 2{radical}5a{sub p} x 2a{sub p} have been observed for {delta} = 0.3-0.4, each exhibiting superstructures related to NdCuO{sub 2.6}. Oxygen vacancy ordering models are proposed to interpret these results. An orthorhombic GdFeO{sub 3}-type phase with {delta} = 0-0.07, the first example of this structure-type in the rare earth cuprates, was found at the highest oxygen pressures investigated. The major structure-types, corresponding to {delta} = 0.07, 0.4, and 0.5, were refined by the Rietveld method. It was not possible to synthesize other LnCuO{sub 3-{delta}} phases for rare earths smaller than Nd at pressures up to 150 kbar. Superconductivity was not observed in any of the new perovskites down to 4.2 K.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 75713
- Journal Information:
- Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 8 Vol. 34; ISSN 0020-1669; ISSN INOCAJ
- Country of Publication:
- United States
- Language:
- English
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