Diffusion path and conduction mechanism of protons in hydroxyapatite

Masatomo Yashima, Naoyuki Kubo, Kazuki Omoto, Hirotaka Fujimori, Kotaro Fujii, Kenji Ohoyama

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)


Calcium hydroxyapatite (HAp, Ca10(PO4) 6(OH)2) is the principal inorganic component of bone and teeth, one of the most important bioceramics, and a proton (H+) conductor with potential for energy conversion devices. The proton diffusion pathway in the HAp lattice is a key to understand the proton conduction mechanism and chemical reaction. Previous neutron-diffraction studies of HAp visualized the short-range proton diffusion pathway. In this work, we report the successful visualization of the long-range proton diffusion pathway in stoichiometric HAp at 923, 673, and 298 K through a combined technique of high-temperature neutron diffraction and bond valence method. We have visualized (1) one-dimensional proton diffusional pathways along the c-axis in the hexagonal channel and (2) two-dimensional proton migration pathway network on the ab-planes at z = 0 and 1/2. The proton diffusion and reorientation of hydroxide ions (OH-) are a complex sinusoidal process in the hexagonal channel along the c-axis, which is consistent with the anisotropic nuclear-density distribution of proton obtained by the neutron diffraction and maximum-entropy method.

Original languageEnglish
Pages (from-to)5180-5187
Number of pages8
JournalJournal of Physical Chemistry C
Issue number10
Publication statusPublished - 2014 Mar 13

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films


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