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High temperature ferroelectric behaviour in α-MnO2 nanorods realised through enriched oxygen vacancy induced non-stoichiometry

Abstract

Nanostructuring followed by the incorporation of defect induced non-stoichiometry is an emerging field of prominence due to its capacity to introduce unprecedented properties in materials with potential applications. In this work, crystalline α-MnO2 nanorods are synthesised using a facile co–precipitation method to exhibit ferroelectric behaviour for the first time. Evolution mechanism of nanorods is investigated using XRD, HRTEM and FTIR spectra, while their thermal stability is probed with TGA/DTA. The novel properties observed is a result of structural rearrangements sparked by electrons in mixed valence cations (Mn3+/Mn4+). The high density of Jahn Teller active Mn3+ breaks the inversion symmetry in α-MnO2 thereby altering atomic environments inducing distortion in the basic MnO6 octahedra. Since, temperature variation XRD analysis confirms phase stability of the crystal structure up to very high temperatures, ferroelectric phase exhibited by the material below Tc is an outcome of combined effects of orbital ordering (OO) of eg electron in Mn3+ and charge ordering (CO) of Mn3+ and Mn4+ cations. This is confirmed using DSC analysis. The breakdown of ferroelectric nature is identified to originate as a result of octahedral tilting as suggested by temperature dependent Raman studies. Magnetic and electrical transport studies give additional evidence of CO ferroelectric phase as they predict the existence of double exchange hopping conduction and surface ferromagnetism in the sample.

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Publication details

The article was received on 22 Aug 2017, accepted on 05 Oct 2017 and first published on 05 Oct 2017


Article type: Paper
DOI: 10.1039/C7CP05724E
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    High temperature ferroelectric behaviour in α-MnO2 nanorods realised through enriched oxygen vacancy induced non-stoichiometry

    R. E. John, A. Chandran, J. George, A. Jose, G. Jose , J. Jose, U. N. V, M. Thomas and G. K C, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP05724E

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