Thermodynamic study of orthorhombic T{sup x} and tetragonal T′ lanthanum cuprate, La{sub 2}CuO{sub 4}

Journal Article · Thu Aug 15 00:00:00 EDT 2013 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2013.05.005· OSTI ID:22274025

Lilova, K. I. ^[1]; Hord, R. ^[2]; Alff, L. ^[3]; Albert, B. ^[2]

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1. Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California, Davis, CA 95616 (United States)
2. Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Technische Universität Darmstadt, Petersenstr. 18, 64287 Darmstadt (Germany)
3. Institute of Materials Science, Technische Universität Darmstadt, Petersenstr. 23, 64287 Darmstadt (Germany)

The enthalpies of transition among the T{sup x}, T′, and T–La{sub 2}CuO{sub 4} phases are obtained from a combination of differential scanning calorimetry, high temperature oxide melt solution calorimetry, and transposed temperature drop calorimetry. The enthalpy of transformation of T{sup x} to T is 2.32±0.07 kJ/mol and the corresponding entropy of transition is 4.38±0.13 J/(mol K). The T′ modification, with an average of 1.40 kJ/mol, is less stable in enthalpy than T{sup x} but at 0.96 kJ/mol, more stable in enthalpy than T. Although we cannot rule out a small stability field at temperatures near the T{sup x}–T transition at 530 K, T′ is most likely metastable at all temperatures. - Graphical abstract: Crystal structure of T{sup x} (orthorhombic), T′ and T (tetragonal) modifications of La{sub 2}CuO{sub 4} (left to right). The space group for orthorhombic T{sup x} is Cmce and I4/mmm for both T′ and T structures; copper cations are presented as small purple, lanthanum as large blue and oxygen as large green circles. Highlights: • The enthalpies of transition among the T{sup x} , T′, and T-La{sub 2}CuO{sub 4} phases are obtained. • The T{sup x} phase is the lowest in energy, the T′ higher and the T highest. • T′ phase is metastable at all temperatures.

• OSTI ID: 22274025
• Journal Information: Journal of Solid State Chemistry, Vol. 204; Other Information: Copyright (c) 2013 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
36 MATERIALS SCIENCE
CALORIMETRY
CATIONS
COPPER
CUPRATES
ENTHALPY
ENTROPY
HIGH-TC SUPERCONDUCTORS
LANTHANUM
LANTHANUM COMPOUNDS
ORTHORHOMBIC LATTICES
OXIDES
SOLUTIONS
SPACE GROUPS
STABILITY
TEMPERATURE RANGE 0400-1000 K
TETRAGONAL LATTICES
THERMODYNAMICS