Investigating the role of GeO2in enhancing the thermal stability and proton mobility of proton-conducting phosphate glasses

Takahisa Omata, Aman Sharma, Takuya Kinoshita, Issei Suzuki, Tomohiro Ishiyama, Shinji Kohara, Koji Ohara, Madoka Ono, Tong Fang, Yang Ren, Masaya Fujioka, Gaoyang Zhao, Junji Nishii

Research output: Contribution to journalArticlepeer-review

Abstract

In this study, the effect of GeO2on the thermal stability and proton mobility (μH) of proton-conducting phosphate glasses was experimentally investigated using 22HO1/2-3NaO1/2-(12 −x)LaO3/2-xGeO2-63PO5/2glasses. Increasing glass transition temperature (Tg) andμHatTgwere experimentally found out, when LaO3/2was substituted with GeO2, and this behavior coincides well with the prediction obtained from a linear regression model previously proposed. Based on the glass structure and nature of a P-O bond, both enhancedTgandμHatTgwere strongly related to the formation of heteroatomic P-O-Ge linkages. The Ge atoms are six-fold coordinated with O atoms, and they tightly bridge the (PO3)nphosphate chains through the heteroatomic P-O-Ge linkages, resulting in rigid phosphate frameworks with higherTg. The formation of the heteroatomic P-O-Ge linkage results in increased covalency in the P-O bond. This increases the ionicity of the O-H bond owing to the balanced electron transfer to prevent excessive decrease in electron density on the O atom in the P-O-H bond. Thus,μHatTgincreases because the increasing ionicity weakens the O-H bond. Herein, the increasing covalency in the P-O bond is discussed according to the difference in the electronegativity and atomic orbitals that contribute to the bond with an O atom between La⋯O and Ge-O bonds.

Original languageEnglish
Pages (from-to)20595-20606
Number of pages12
JournalJournal of Materials Chemistry A
Volume9
Issue number36
DOIs
Publication statusPublished - 2021 Sep 28

ASJC Scopus subject areas

  • Chemistry(all)
  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)

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