Thermal stability of MnO2 polymorphs

研究成果: Article査読

抄録

This study reports thermal stability of α, β, γ, δ, and λ-type MnO2 polymorphs investigated using differential scanning calorimetry (DSC) and in-situ high-temperature X-ray diffraction measurement (HTXRD). These experiments revealed that the thermal stability of the polymorphs is in the following order: β ​> ​α ​> ​γ ​> ​δ ​≈ ​λ. The β-MnO2 phase (1 ​× ​1 tunnel, rutile structure), the most stable form between the MnO2 polymorphs, maintains the structure up to 500 ​°C until oxygen release causes phase transformation to Mn2O3. The α-MnO2 phase (2 ​× ​2 and 1 ​× ​1 tunnel structure) exhibits high thermal stability comparable to the β phase, despite its large vacant 2 ​× ​2 tunnel. The γ-MnO2 phase (mixed microdomain structure of 2 ​× ​1 tunnel and 1 ​× ​1 tunnel) shows a stepwise transformation into β-MnO2 from 400 ​°C after structure relaxation. The δ-MnO2 phase (layered structure) is easily destabilized by extracting interlayer K ions, resultingly, to lose the interlayer periodicity below 200 ​°C, while each layer itself is preserved up to ∼500 ​°C. The λ-MnO2 phase (defect spinel structure) is thermally unstable and transforms into β-MnO2 around 250 ​°C, and subsequently decomposes to Mn2O3 above the temperature. The thermal stability of MnO2 polymorphs is discussed in terms of the bonding environment of oxide ions.

本文言語English
論文番号122683
ジャーナルJournal of Solid State Chemistry
305
DOI
出版ステータスPublished - 2022 1

ASJC Scopus subject areas

  • 電子材料、光学材料、および磁性材料
  • セラミックおよび複合材料
  • 凝縮系物理学
  • 物理化学および理論化学
  • 無機化学
  • 材料化学

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