Abstract

Search of new thermoelectric (TE) materials with high figure-of-merit (ZT) is always inspired the researcher in TE field. Here, we present a combined experimental and theoretical study of TE properties on Na_0.74CoO₂ compound in high temperature region. The experimental Seebeck coefficient (S) is found to vary from 64 to 118 μV/K in the temperature range 300−620 K. The observed value of thermal conductivity (κ) is ~2.2 W/m-K at 300 K. In the temperature region 300−430 K, the value of κ increases up to ~2.6 W/m-K and then decreases slowly till 620 K with the corresponding value of ~2.4 W/m-K. We have also carried out the theoretical calculations and the best matching between experimental and calculated values of transport properties are observed in spin-polarized calculation within DFT + U by chosen U = 4 eV. The maximum calculated value of ZT is found to be ~0.67 at 1200 K for p-type conduction. Our computational study suggests that the possibility of n-type behaviour of the compound which can lead to a large value of ZT at higher temperature region. Electron doping of ~5.1 × 10²⁰ cm⁻³ is expected to give rise the high ZT value of ~2.7 at 1200 K. Using these temperature dependent ZT values, we have calculated the maximum possible values of efficiency (η) of thermoelectric generator (TEG) made by p and n-type Na_0.74CoO₂. The present study suggests that one can get the efficiency of a TE cell as high as ~11% when the cold and hot end temperature are fixed at 300 and 1200 K, respectively. Such high values of ZT and efficiency suggest that Na_0.74CoO₂ can be used as a potential candidate for high temperature TE applications.

Graphical abstract

中文翻译：

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探索提高Na 0.74 CoO 2的品质因数（> 2）的可能性：结合实验和理论研究

摘要

具有高品质因数（ZT）的新型热电（TE）材料的搜索始终激发着TE领域的研究人员的灵感。在这里，我们提出了在高温区域Na _0.74 CoO ₂化合物的TE性质的组合实验和理论研究。实验塞贝克系数（S）被发现，以改变从64至118 μ V / K的温度范围300-620 K.所观察到的热导率（的值κ）是〜2.2 W / mK的在300K在温度区域300−430 K，κ的值上升至〜2.6 W / mK，然后缓慢下降至620 K，对应值为〜2.4 W / mK。我们还进行了理论计算，并且通过选择U = 4 eV在DFT + U内的自旋极化计算中观察到了传输性质的实验值与计算值之间的最佳匹配。对于p型传导，ZT的最大计算值在1200 K下约为0.67。我们的计算研究表明，该化合物可能会在较高温度区域导致ZT值较大，而出现n型行为。电子掺杂〜5.1×10 ²⁰ cm ^-3预期在1200 K时会产生约2.7的高ZT值。使用这些与温度相关的ZT值，我们计算出了由p型和n型Na _0.74制成的热电发电机（TEG）的效率（η）的最大可能值。CoO ₂。本研究表明，当冷端温度和热端温度分别固定为300 K和1200 K时，TE电池的效率可高达11％。如此高的ZT值和效率表明，Na _0.74 CoO ₂可用作高温TE应用的潜在候选者。

图形概要