Preparation and Characterization of γ-NaxCoO2 by Sodium Polyacrylate Gel Method

doi:10.15541/jim20160474

Abstract

Abstract:

Chemical synthesis method of sodium polyacrylate (PAAS) gel method was used to prepare γ-Na_xCoO₂ powders. The effects of PAAS/Co²⁺molar ratio, concentration of raw materials and calcination temperatures on the phase composition and microstructure of product were studied. Na_xCoO₂ polycrystalline samples with different Na⁺ concentrations were synthesized by the above method, and the thermoelectric properties were characterized. The results showed that the PAAS/Co²⁺molar ratio greatly affected the phase composition. With the increase of PAAS/Co²⁺molar ratio, the phase composition of sample was transformed from Co₃O₄ to γ-Na_xCoO₂. The proper molar ratio of PAAS/Co²⁺ to obtain γ-Na_xCoO₂ single phase is 0.8. the phase composition of sample will change slightly with different concentrations of raw materials. γ-Na_xCoO₂ single phase was formed at low concentration of raw materials (below 0.025 mol/L), however, when the concentration exceeded 0.025 mol/L, the second phase was formed. The formation of γ-Na_xCoO₂ single phase was promoted with the increase of calcination temperature. The γ-Na_xCoO₂ powders calcined at 800℃ were plate-like particles with about 200 nm in thickness and about 1-4 μm in width along the plane direction. With the increase of Na content in samples, σ value and S value were increased while κ value was decreased, leading to a significant increase in ZT value.

Key words: sodium polyacrylate gel method, γ-Na_xCoO₂, thermoelectric materials

CLC Number:

TQ174

LI Xiao-Yu, ZHANG Li, TANG Xin-Feng, ZHANG Qing-Jie. Preparation and Characterization of γ-Na_xCoO₂ by Sodium Polyacrylate Gel Method[J]. Journal of Inorganic Materials, 2017, 32(6): 603-608.

Figures/Tables 8

Fig. 1 XRD patterns of samples prepared with different PAAS/ Co2+ molar ratios(a) 0.5; (b) 0.6; (c) 0.7; (d) 0.8; (e) 0.9; (f) 1.0; (g) 1.1

Table 1 ICP-AES results of Na content

Nominal Na content, x	Actual Na content, x
0.8	0.784
0.9	0.878
1.0	0.977

Fig. 2 SEM images of samples prepared with different PAAS/ Co2+ molar ratios(a) 0.8; (b) 0.9; (c) 1.0; (d) 1.1

Fig. 3 XRD patterns of samples with different source concentrations(A) (a) 0.025 mol/L; (b) 0.020 mol/L; (c) 0.013 mol/L; (B) (a) 0.05 mol/L; (b) 0.033 mol/L; (c) 0.025 mol/L

Fig. 4 SEM images of samples prepared with different PAAS source concentrations(a) 0.025mol/L; (b) 0.02mol/L; (c) 0.033mol/L

Fig. 5 XRD patterns of samples calcined at different temperatures(a) Precusor; (b) 400℃; (c) 500℃; (d) 600℃; (e) 700℃; (f) 800℃

Fig. 6 SEM images of products calcined from precursor at different temperatures(a) 400℃; (b) 500℃; (c) 600℃; (d) 700℃; (e) 800℃

Fig. 7 Temperature dependence of the electrothermal transport properties for samples with different PAAS/Co2+ mole ratios

References 15

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Preparation and Characterization of γ-Na_xCoO₂ by Sodium Polyacrylate Gel Method

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