Synthesis of Ca–Co hydroxides and their use in facile fabrication of textured CayCoO2 thermoelectric ceramics

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Abstract

A brucite-type hydroxide of CazCo1−z(OH)2 with a high Ca content was synthesized and utilized as a single-source precursor for the fabrication of bulk ceramics of a semiconducting layered calcium cobaltite CayCoO2. Plate-like CazCo1−z(OH)2 particles with z up to 0.22 were reproducibly obtained by a reverse co-precipitation method using KOH as an alkaline source. Uniaxial pressing of the plate-like CazCo1−z(OH)2 particles (z = 0.22), which was calcined at 373 K beforehand, at a pressure as high as 500 MPa produced a highly dense green pellet where the plate-like particles were stacked along the pressing direction. The green pellet was then converted by a heat treatment at 923 K into an oxide ceramic of preferentially (010)-oriented CayCoO2 via a topotactic-like pyrolytic reaction maintaining edge-sharing CoO6 octahedra. Although the ceramic also contained a minor insulating Co3O4 phase (16.7 ± 0.7 mol% estimated from thermal analysis), the electrical measurements proved its p-type semiconducting behavior resulting from the CayCoO2 phase with enhanced Seebeck coefficient exceeding 160 μV/K at room temperature.

Original languageEnglish
JournalCeramics International
DOIs
Publication statusAccepted/In press - 2018 Jan 1

Keywords

  • A. Powders: solid state reaction
  • C. Electrical properties
  • D. Transition metal oxides
  • Thermoelectric properties

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Process Chemistry and Technology
  • Surfaces, Coatings and Films
  • Materials Chemistry

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