Crystal Structure and Transport Properties of γ-NaxCoO2(x=0.67-0.75)
Crystal Structure and Transport Properties of γ-NaxCoO2(x=0.67-0.75)
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γ-NaxCoO2(x=0.67-0.75)的晶体结构和输运性质
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
T. Kajitani
中科院分区：
文献类型：
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作者：
Y. Ono;N. Kato;Y. Ishii;Y. Miyazaki;T. Kajitani
研究了γ-NaxCoO_2在x=0.67-0.75范围内的晶体结构和输运性质。单相样品通过烧结原料Na 2CO 3（99.5%）和Co 3 O 4（99.9%）的混合物制备。通过电感耦合等离子体（ICP）分析测定Na/Co组成比（x）。的晶体结构参数进行了细化粉末中子衍射强度的Rietveld分析，假设P63/mmc型空间对称性。除了Na含量外，晶体结构几乎没有变化。在380 ~ 1000 K温度范围内，分别用标准四探针法和温度梯度法测量了样品的电阻率ρ和塞贝克系数S。ρ-T曲线在初始测量时表现出热滞后现象。但是，在下面的测量中，热滞后被显著抑制。在任何温度下，x = 0.75的样品中的S略高于其他样品。功率因数（S2/ρ）在x = 0.75时达到最大值（980 K时为5.3 × 10-4 W/mK2）。热压工艺可以有效地消除ρ的热滞效应，提高功率因数。
Crystal structure and transport properties of γ-NaxCoO2 have been studied in the range of x=0.67-0.75. Single-phase samples were prepared by sintering mixture of raw materials, Na2CO3 (99.5%) and Co3O4 (99.9%). Na/Co composition ratio (x) was determined by inductively coupled plasma (ICP) analysis. The crystal structure parameters were refined by Rietveld analysis of powder neutron diffraction intensities, assuming P63/mmc type space symmetry. Little changes in the crystal structure are noticed, except for Na contents. Electric resistivity ρ and Seebeck coefficient S were measured at temperatures between 380 K and 1000 K by the standard four-probe method and temperature-gradient method, respectively. The ρ-T curves exhibit the thermal hysteresis in the initial measurement. But, in the following measurement, the thermal hysteresis is significantly surpressed. The S was slightly higher in the sample with x = 0.75 than in the others at any temperatures. Power factor (S2/ρ) reaches its maximum value at x = 0.75 (5.3 × 10-4 W/mK2 at 980 K). Hot pressing technique is effective in removing the thermal hysteresis of ρ as well as increasing the power factor.