Thermodynamics of CoAl{sub 2}O{sub 4}-CoGa{sub 2}O{sub 4} solid solutions

Journal Article · Tue Jun 15 00:00:00 EDT 2010 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2010.03.040· OSTI ID:21421510

Navrotsky, Alexandra ^[1]; Melot, Brent C; Seshadri, Ram ^[2]

---

1. Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California, Davis, CA 95616 (United States)
2. Materials Department and Materials Research Laboratory, University of California, Santa Barbara, CA 93106 (United States)

CoAl{sub 2}O{sub 4}, CoGa{sub 2}O{sub 4}, and their solid solution Co(Ga{sub z}Al{sub 1-z}){sub 2}O{sub 4} have been studied using high temperature oxide melt solution calorimetry in molten 2PbO.B{sub 2}O{sub 3} at 973 K. There is an approximately linear correlation between lattice parameters, enthalpy of formation from oxides, and the Ga content. The experimental enthalpy of mixing is zero within experimental error. The cation distribution parameters are calculated using the O'Neill and Navrotsky thermodynamic model. The enthalpies of mixing calculated from these parameters are small and consistent with the calorimetric data. The entropies of mixing are calculated from site occupancies and compared to those for a random mixture of Ga and Al ions on octahedral site with all Co tetrahedral and for a completely random mixture of all cations on both sites. Despite a zero heat of mixing, the solid solution is not ideal in that activities do not obey Raoult's Law because of the more complex entropy of mixing. - Graphical abstract: Measured enthalpies of mixing of CoAl{sub 2}O{sub 4}-CoGa{sub 2}O{sub 4} solid solutions are close to zero but entropies of mixing reflect the complex cation distribution, so the system is not an ideal solution.

• OSTI ID: 21421510
• Journal Information: Journal of Solid State Chemistry, Vol. 183, Issue 6; Other Information: DOI: 10.1016/j.jssc.2010.03.040; PII: S0022-4596(10)00130-1; Copyright (c) 2010 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM COMPOUNDS
ALUMINIUM IONS
BORON OXIDES
CALORIMETRY
CATIONS
COBALT COMPOUNDS
ENTROPY
FORMATION HEAT
GERMANIUM COMPOUNDS
LATTICE PARAMETERS
MIXING
MIXING HEAT
OXIDES
SOLID SOLUTIONS
SPINELS
TEMPERATURE RANGE 0400-1000 K
THERMODYNAMIC MODEL
THERMODYNAMICS
BORON COMPOUNDS
CHALCOGENIDES
CHARGED PARTICLES
DISPERSIONS
ENTHALPY
HOMOGENEOUS MIXTURES
IONS
MATHEMATICAL MODELS
MINERALS
MIXTURES
OXIDE MINERALS
OXYGEN COMPOUNDS
PARTICLE MODELS
PHYSICAL PROPERTIES
REACTION HEAT
SOLUTIONS
STATISTICAL MODELS
TEMPERATURE RANGE
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS