Energetics of T, T[prime], and T* phases in some rare earth cuprates
- Princeton Univ., NJ (United States)
- International Business Machines Corp., Yorktown Heights, NY (United States)
The enthalpies of solution in molten 2PbO[center dot]B[sub 2]O[sub 3] at 704[degrees]C of Nd[sub 2]CuO[sub 4] (T[prime]), (La[sub 1[minus]x]Nd[sub x])[sub 2]CuO[sub 4] (T or T[prime]), (La[sub 0.60]Dy[sub 0.35])Ce[sub 0.05][sub 2]CuO[sub 4] (T[prime] and T*), and (La[sub 0.60]Dy[sub 0.35]Th[sub 0.05])[sub 2]CuO[sub 4] (T[prime] and T*) have been measured. The enthalpy of formation (from oxides) at 700[degrees]C of (La[sub 1[minus]x]Nd[sub x])[sub 2]CuO[sub 4] (0 [le] x [le] 1) varies from [minus]20 to [minus]7 kJ mol[sup [minus]1], depending on composition. The enthalpy of the T[prime] to T transition in (La[sub 0.75]Nd[sub 0.25])[sub 2]CuO[sub 4] is +6.3 [+-] 2.8 kJ mol[sup [minus]1]. Extrapolated enthalpies of transition from T[prime] to T are +3[+-]8 kJ mol[sup [minus]1] for La[sub 2]CuO[sub 4] and +28[+-]10 kJ mol[sup [minus]1] for Nd[sub 2]CuO[sub 4]. The enthalpy of mixing in the T[prime] phase of (La[sub 1[minus]x]Nd[sub x])[sub 2]CuO[sub 4] is positive, with a regular enthalpy interaction parameter of +51.8 kJ mol[sup [minus]1]. The positive enthalpy of mixing argues against cation ordering being important in this system. The enthalpies of transition of T* to T[prime] of (La[sub 0.6]Dy[sub 0.35]Th[sub 0.05])[sub 2]CuO[sub 4] and (La[sub 0.6]Dy[sub 0.35]Ce[sub 0.05])[sub 2]CuO[sub 4] are +38[+-]5 and +51[+-]6 kJ mol[sup [minus]1], respectively. There is a linear dependence of the enthalpy of transition ([Delta]H) between T[prime] and T (or T* and T[prime]) phases on the volume of transition ([Delta]V), [Delta]H (kJ mol[sup [minus]1]) = 37.4 + 9.27 [Delta]V (cm[sup 3] mol[sup [minus]1]). 31 refs., 4 figs., 5 tabs.
- DOE Contract Number:
- FG02-89ER45394
- OSTI ID:
- 5845798
- Journal Information:
- Journal of Solid State Chemistry; (United States), Journal Name: Journal of Solid State Chemistry; (United States) Vol. 104:2; ISSN 0022-4596; ISSN JSSCBI
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACTINIDE COMPOUNDS
BORATES
BORON COMPOUNDS
CERIUM COMPOUNDS
CHALCOGENIDES
COPPER COMPOUNDS
CUPRATES
DYSPROSIUM COMPOUNDS
ENTHALPY
FORMATION HEAT
LANTHANUM COMPOUNDS
LEAD COMPOUNDS
LEAD OXIDES
MIXING HEAT
NEODYMIUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
REACTION HEAT
SOLUTION HEAT
STOICHIOMETRY
THERMODYNAMIC PROPERTIES
THORIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS