Experimental heat capacities, excess entropies, and magnetic properties of bulk and nano Fe3O4-Co3O4 and Fe3O4-Mn3O4 spinel solid solutions

• Published in: Journal of solid state chemistry Vol. 259; no. C; pp. 79 - 90
• Main Authors: Schliesser, Jacob M., Huang, Baiyu, Sahu, Sulata K., Asplund, Megan, Navrotsky, Alexandra, Woodfield, Brian F.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2018; Elsevier
• Subjects: Entropy of mixing; Heat capacity; Nanoparticle; Spinel solid solutions; Entropy of mixing; Heat capacity; Nanoparticle; Spinel solid solutions
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2018.01.007

We have measured the heat capacities of several well-characterized bulk and nanophase Fe3O4-Co3O4 and Fe3O4-Mn3O4 spinel solid solution samples from which magnetic properties of transitions and third-law entropies have been determined. The magnetic transitions show several features common to effects of particle and magnetic domain sizes. From the standard molar entropies, excess entropies of mixing have been generated for these solid solutions and compared with configurational entropies determined previously by assuming appropriate cation and valence distributions. The vibrational and magnetic excess entropies for bulk materials are comparable in magnitude to the respective configurational entropies indicating that excess entropies of mixing must be included when analyzing entropies of mixing. The excess entropies for nanophase materials are even larger than the configurational entropies. Changes in valence, cation distribution, bonding and microstructure between the mixing ions are the likely sources of the positive excess entropies of mixing. [Display omitted] •Effect of mixing on the total entropy for both nano and bulk solid solutions was investigated for the first time.•Magnetic properties of transitions and third-law entropies were determined.•Excess entropies of mixing were generated and compared with configurational entropies.•Sources of positive excess entropies of mixing were discussed.