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

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 Tmore » highest. • T′ phase is metastable at all temperatures.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [1]
  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)
Publication Date:
OSTI Identifier:
22274025
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 204; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
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