A new crossover in Fe(3)O(4) magnetite under pressure near 6 GPa: modification to 'ideal' inverse cubic spinel?

作者：Ovsyannikov Sergey V^*; Shchennikov Vladimir V; Todo Sakae; Uwatoko Yoshiya

来源：Journal of Physics: Condensed Matter , 2008, 20(17): 172201.

DOI：10.1088/0953-8984/20/17/172201

The results of the first study on the thermoelectric power (Seebeck effect) of single crystals of Fe(3)O(4) magnetite at high pressure P up to 20 GPa and room temperature are reported. The electrical resistance and a sample's contraction (relative compressibility) were also investigated over a P range of 0-20 GPa. A smooth bend (crossover) in the pressure dependence of the thermopower was firmly established near 6 GPa. This feature was attributed to a modification of Fe(3)O(4) to an 'ideal' inverse configuration, the case where equivalent amounts of charges (the Fe(2+) ions) and vacancies (the Fe(3+) ions) at the octahedral sites provide nearly metallic polaron hopping conductivity via the octahedral network. The origin of this transformation might lie in (i) a P-tuning 'perfection' of the electronic transport in the inverse spinel, and/or in (ii) a transfer of a minor group of the charges from the tetrahedral sites to the octahedral ones, i. e. a normal -> inverse configuration transition. Opportunities for the opposite valence transition in magnetite, from the inverse spinel to the normal (direct) one, are also discussed. At ambient pressure the samples of Fe(3)O(4) were probed by Raman spectroscopy and using the electrical resistivity across the Verwey transition.

• 出版日期2008-4-30