Layered cobalt oxide epitaxial films exhibiting thermoelectric ZT = 0.11 at room temperature,Journal of Materials Chemistry A

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Layered cobalt oxide epitaxial films exhibiting thermoelectric ZT = 0.11 at room temperature
Journal of Materials Chemistry A ( IF 10.7 ) Pub Date : 2020-10-13 , DOI: 10.1039/d0ta07565e
Yugo Takashima _{1,

2,

3,

4} , Yu-qiao Zhang _{2,

4,

5,

6} , Jiake Wei _{4,

7,

8,

9,

10} , Bin Feng _{4,

7,

8,

9} , Yuichi Ikuhara _{4,

7,

8,

9,

10} , Hai Jun Cho _{1,

2,

3,

4,

5} , Hiromichi Ohta _{1,

2,

3,

4,

5}

Affiliation

Among many thermoelectric materials, oxide-based materials draw significant interest due to their environmental compatibility. In particular, layered cobaltite, Na_0.75CoO₂, shows a large thermoelectric power factor parallel to the layers. However, the thermal conductivity (κ) is rather high (5–7 W m⁻¹ K⁻¹), and therefore, its thermoelectric figure of merit ZT is small (∼0.03) at room temperature. Here we show that substituting the Na⁺ ion with the Ba²⁺ ion in Na_xCoO₂ drastically reduces the κ while keeping the large power factor, resulting in a large enhancement in ZT. We fabricated epitaxial films of Na_0.75CoO₂ by the reactive solid-phase epitaxy method and performed ion-exchange treatment from Na⁺ to Ba²⁺ to synthesize Ba_0.27CoO₂ films. The room temperature electrical conductivity (σ), thermopower (S), and power factor of the c-axis oriented Ba_0.27CoO₂ films along the in-plane direction were 2310 S cm⁻¹, +72 μV K⁻¹, and 1.2 mW m⁻¹ K⁻², respectively, while the κ along the in-plane, which was clarified by measuring the κ of the c-axis inclined (55°) film, was 3.3 W m⁻¹ K⁻¹. This yields a ZT (= S²σT/κ) value along the in-plane as high as 0.11 at room temperature, which is the highest among those reported for oxide thermoelectric materials except oxychalcogenide (BiO)(CuSe).

中文翻译：

在室温下表现出热电ZT = 0.11的层状氧化钴外延膜

在许多热电材料中，基于氧化物的材料由于其环境相容性而引起了极大的兴趣。特别地，层状钴Na _0.75 CoO ₂显示出平行于层的大的热电功率因数。但是，热导率（κ）很高（5-7 W m ^-1 K ^-1），因此，其在室温下的热电系数ZT小（〜0.03）。在这里，我们显示在Na _x CoO ₂中将Na ⁺离子替换为Ba ²⁺离子会大大降低κ同时保持较大的功率因数，从而大幅提高ZT。通过反应固相外延法制备了Na _0.75 CoO ₂外延膜，并进行了从Na ⁺到Ba ^2+的离子交换处理，合成了Ba _0.27 CoO ₂膜。c轴取向Ba _0.27 CoO ₂膜的面内方向的室温电导率（σ），热功率（S）和功率因数分别为2310S cm ^-1，+72μVK ^-1和1.2。 mW m ^-1 K^-2，分别，而κ沿面内，这是通过测量澄清κ所述的Ç轴倾斜（55°）膜，是为3.3W米^-1 ķ^-1。这产生一个ZT（=小号² σT / κ一起）值的面内高达0.11在室温下，这是所报道的氧化物热电材料除了氧硫属化合物（BIO）（的CuSe）中最高的。

更新日期：2020-11-03

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