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La2CuO4+δ: Synthesis under high oxygen pressure and study of phase relations and energetics

Published online by Cambridge University Press:  03 March 2011

R.P. Rapp ,
A. Mehta ,
J. DiCarlo  and
A. Navrotsky
R.P. Rapp*
Affiliation:
Department of Geological and Geophysical Sciences and Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544–1003
A. Mehta
Affiliation:
Department of Geological and Geophysical Sciences and Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544–1003
J. DiCarlo
Affiliation:
Department of Geological and Geophysical Sciences and Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544–1003
A. Navrotsky*
Affiliation:
Department of Geological and Geophysical Sciences and Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544–1003
*
a)Also at the Center for High Pressure Research, an NSF Science and Technology Center, Princeton University, Princeton, New Jersey 08544–1003.
a)Also at the Center for High Pressure Research, an NSF Science and Technology Center, Princeton University, Princeton, New Jersey 08544–1003.
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Abstract

High oxygen pressures have been achieved in a piston-cylinder apparatus using a double capsule assembly consisting of a sealed outer Au capsule, containing an oxygen source (KMnO4), and an inner, open Pt capsule containing the sample. Using this technique, La2CuO4 was annealed at 800 °C, 5–25 kbar for 2–4 h. Transposed temperature drop calorimetry at 704 °C was used to determine the enthalpy of oxidation, and weight loss measurements characterized the oxygen nonstoichiometry, δ, in La2CuO4+δ, in the high-pressure, oxygen-annealed samples. For samples analyzed at room temperature, x-ray diffraction measurements show that beyond δ ≍ 0.10–0.13, additional oxygen is accommodated in a perovskite-like LaCuO3−α phase. An analysis of the thermochemical measurements indicates that the nature of holes in La2CuO4+δ could change in the range of δ ≍ 0.03–0.06.16,17 It is further suggested that the observed change in the thermochemical behavior in the range of δ ≍ 0.03–0.06 could be the driving influence behind the spinodal decomposition of La2CuO4+δ at low temperatures (Dabrowski et al.10).

Type
Articles
Information
Journal of Materials Research , Volume 9 , Issue 1 , January 1994 , pp. 8 - 12
Copyright
Copyright © Materials Research Society 1994

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References

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