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Title: Influence of O-Co-O layer thickness on the thermal conductivity of Na{sub x}Co{sub 2}O{sub 4} studied by positron annihilation

Nominal stoichiometric Na{sub x}Co{sub 2}O{sub 4} (x = 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0) polycrystals were synthesized by a solid-state reaction method. They were further pressed into pellets by the spark plasma sintering. The crystal structure and morphology of Na{sub x}Co{sub 2}O{sub 4} samples were characterized by X-ray diffraction and scanning electron microscopy measurements. Good crystallinity and layered structures were observed for all the samples. Positron annihilation measurements were performed for Na{sub x}Co{sub 2}O{sub 4} as a function of Na content. Two lifetime components are resolved. τ{sub 1} is attributed mainly to positron annihilation in the O-Co-O layers and shifts to Na layers only in the H3 phase. The second lifetime τ{sub 2} is due to positron annihilation in vacancy clusters which may exist in the Na layers or grain boundary region. The size of vacancy clusters grow larger but their concentration decreases with increasing Na content in the range of 1.0 < x < 1.8. The thickness of O-Co-O layer also shows continuous increase with increasing Na content, which is reflected by the increase of τ{sub 1}. The thermal conductivity κ, on the other hand, shows systematic decrease with increasing Na content. This suggests that the increasing spacing of O-Co-O layer could effectively reducemore » the thermal conductivity of Na{sub x}Co{sub 2}O{sub 4}.« less
Authors:
; ; ; ; ;  [1] ; ;  [2]
  1. Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 (China)
  2. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China)
Publication Date:
OSTI Identifier:
22490801
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 3; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABUNDANCE; ELECTRON-POSITRON INTERACTIONS; GRAIN BOUNDARIES; LAYERS; PLASMA; POLYCRYSTALS; PRESSES; SCANNING ELECTRON MICROSCOPY; SINTERING; SPECTROSCOPY; STOICHIOMETRY; THICKNESS; X-RAY DIFFRACTION