High resolution and in situ neutron powder diffraction study of the crystal structure and the stability of Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}}

Journal Article · Tue Nov 15 00:00:00 EST 2005 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2005.07.010· OSTI ID:20784753

Xuan, H Nguyen ^[1]; Galez, Ph ^[1]; Pisch, A ^[2]; Bertrand, Ch ^[1]; Beauquis, S ^[1]; Soubeyroux, J L ^[3]; Bouree-Vigneron, F ^[4]

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1. LAIMAN-ESIA, Universite de Savoie, BP 806, F-74016 Annecy Cedex (France)
2. LTPCM, UMR 5614, CNRS-INPG-UJF, 1130 Rue de la Piscine, F-38402 Saint Martin d'Heres (France)
3. Laboratoire de Cristallographie, CNRS, BP 166, F-38042 Grenoble Cedex 9 (France)
4. LLB, CEA-CNRS, CEA-Saclay, F-91191 Gif-sur-Yvette (France)

The crystal structure and stability of Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}} have been investigated by neutron powder diffraction, differential thermal analysis and thermogravimetry. It is found that the phase is not stable below 1065K in p(O{sub 2})=1bar and decomposes according to the eutectoid reaction Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}}+x O{sub 2}-bar Ba{sub 2}CuO{sub 3.4}+CaO+2BaCuO{sub 2}. However, the equilibrium with the outer gas is not reached for sintered ceramics so that Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}} can be obtained in a metastable state after normal cooling conditions. In this case, the crystal structure is cubic (Im-3m, a=8.1452(1)A, {delta}=0.68, Z=2, R{sub wp}=2.5%, R{sub Bragg}=5.4%) as reported in the literature. In reduced oxygen partial pressure (p(O{sub 2})<10{sup -6}bar), Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}} is stable down to room temperature and has a tetragonal structure with a significant lower oxygen content (P4/mmm, a=8.1976(3)A, c=8.0709(3)A, {delta}=-0.81, Z=2, R{sub wp}=2.8%, R{sub Bragg}=5.1%). The difference between the two crystal structures is discussed in terms of oxygen content, copper formal valence and cation coordination. The influence of the oxygen pressure on the stability of Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}} is also discussed.

• OSTI ID: 20784753
• Journal Information: Journal of Solid State Chemistry, Vol. 178, Issue 11; Other Information: DOI: 10.1016/j.jssc.2005.07.010; PII: S0022-4596(05)00314-2; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BARIUM COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM OXIDES
CERAMICS
COPPER OXIDES
METASTABLE STATES
NEUTRON DIFFRACTION
OXYGEN
PARTIAL PRESSURE
STABILITY
TETRAGONAL LATTICES
THERMAL GRAVIMETRIC ANALYSIS