Defect Chemistry of " BaCuO₂" I. Oxygen Non -Stoichiometry, Cation Molecularity and X-ray Diffraction Determinations

Abstract

“BaCuO2” is the key intermediate in the synthesis of the Ba2YCu3O7−δ superconductor. Its very complex crystal structure is able to accommodate a large change in oxygen content. Oxygen non-stoichiometry of "BaCuO2" materials with 1:1 and 88:90 (Ba :Cu) molecularity has been investigated by polythermal X-ray powder diffraction coupled with isobaric-isothermal gravimetry determinations under different temperature and oxygen partial pressure conditions [300≤ T≤ 820 °C, 1 ≥ P(O2) ≥ 3 • 10-3 atm]. The 1:1 composition does not give well reproducible results, thus suggesting its polyphasic nature, at least in part of the investigated range. The results for the 88:90 ≅ 0.98 (Ba :Cu) composi­ tion are well reproducible and show that the material is single phase. Ba0.98CuO1.98 + δ is oxygen over-stoichiometric in the whole investigated [T, P(O2)] range, with a maximum value δ∼0.21. A Rietveld X-ray profile fitting is in agreement with previous single-crystal data. The trend of δ vs. P(O2) is consistent with the presence of oxygen interstitial defects on (possibly different) crystallographic sites.

Zirconia‐Based Metastable Solid Solutions through Self‐Propagating High‐Temperature Synthesis: Synthesis, Characterization, and Mechanistic Investigations

“…The analysis was performed using a homemade, high-accuracy symmetrical thermogravimetric apparatus based on a Cahn 2000 electrobalance. 16 About 40 mg of solid solution placed in a platinum sample holder was used in the thermogravimetric apparatus which was operated under a flux of a high-purity mixture of argon with 5 vol% hydrogen. The temperature of the sample was then increased linearly up to 530°C and maintained at this value until a constant weight was reached, typically in about 60 -90 min.…”