Interplay between Local Electronic Configuration and the Occurrence of a Metallic State: An Experimental Approach
✍ Scribed by Jean-Pierre Doumerc; Jean-Claude Grenier; Paul Hagenmuller; Michel Pouchard; Antoine Villesuzanne
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 218 KB
- Volume
- 147
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
Assuming that structural distortions are involved in a large class of metal+insulator transitions as well as in the stabilization of the local electronic con5guration of a given cation leads the authors to look for a chemical system appropriate for investigating the interplay between both e4ects. The chosen cobaltite, TlSr 2 CoO 5 , undergoes a 5rst order phase transition near room temperature involving steep changes and a hysteresis loop in the temperature dependencies of the magnetic susceptibility and of the electrical resistivity. The low temperature o-phase is an antiferromagnetic semiconductor and the high temperature tphase is a metal with dominant ferromagnetic interactions. Electronic structure was calculated using the extended HuK ckel tightbinding method. The metallic character of the t-phase can be explained by the delocalization of some of the d-electrons of Co 3؉ -ions in a * x 2 ؊y 2 band and the strong ferromagnetic interactions can be ascribed to an indirect coupling of the localized moments via itinerant electrons. The electronic con5guration of cobalt ions can be regarded as intermediate between high-spin and intermediate-spin states in the t-phase. In the low temperature phase it disproportionates into a purely high-spin state and a purely intermediate-spin state for Co 3؉ ions located in two di4erent sites, the features of which respectively accommodate each electronic con5guration.