Improvement in Energy Conversion Efficiency of Layered Oxide Thermoelectrics Through Self-assembled Texturing

具有ZnO-In_2 O_3的层结构通过通量方法成功生长的单一晶体，并被确认为平面内的电气导电性是两个等级的强度大于跨平面导电性。Y-掺杂的单晶体已经找到了与纹理陶瓷类似的平面上的行为，并且已经验证了半数量的ZT，该系统将能够最大限度地实现~ 0.5.我们成功地准备了Na_CoO_2的高质量基本薄<0.8>薄膜，使我们能够合成人性稳定的Sr_xCoO_2薄膜和<0.3>Na_CoO_2·1.3H_2O以展示低于4K的超行为。我们也成功地合成了Ca_3Co_4O_9的外延薄膜的热电属性与那些块状单晶体相比。我们实验上确认了重Nb-掺杂SrTiO_3 （STO）的最大ZT可能在1，000 K上达到0.37。在进一步提高转换效率的情况下， Eu^&lt;2+&gt; ions，任何电离辐射与Sr^&lt;2+&gt;相似，已成功地替代Sr^&lt;2+&gt; ions，在不影响电子运输的情况下保持热传导性的同时，在不影响电子运输的情况下，将功率因素增加到ZT上升到0.39 at 1，我们在TiO_2/SrTiO_3接口上发现了一种由两尺寸电子气体（2DEG）制成的巨型Seebeck协同作用大约5次，因为它是一个块状单晶体。我们在超晶格组合的未掺杂STO和NB-掺杂STO中进一步成功，并验证了一个单元单元层的NB-掺杂STO展品4.4次作为较大的Seebeck协同作用作为一个大块单一晶体。ZT在室内的温度估计是采用单晶体的热条件2.4这是热电能量转换的世界纪录。

Single crystals of homologous phase in the ZnO-In_2O_3 with layer structures were successfully grown by a flux method, and it was confirmed that the in-plane electrical conductivity is two orders of magnitude larger than cross-plane conductivity. Y-doped single crystal was found to show the in-plane conductivity similar to that of textured ceramic, and it was verified semi-quantitatively that ZT of this system would be ultimately achieved to be〜0.5.We have succeeded in preparing high-quality epitaxial thin films of Na_<0.8>CoO_2, which further enabled us to synthesize humidity-stable Sr_xCoO_2 thin films and Na_<0.3>CoO_2・1.3H_2O exhibiting superconductivity below 4 K. We also succeeded in synthesizing epitaxial thin films of Ca_3Co_4O_9 whose thermoelectric properties are comparable to those of a bulk single crystal.We have experimentally confirmed that the maximum ZT of heavily Nb-doped SrTiO_3 (STO) could be 0.37 at 1,000 K. In order to further improve the conversion efficiency, Eu^<2+> ions, whose ionic radius is similar to Sr^<2+>, were successfully substituted for Sr^<2+> ions to reduce thermal conductivity while maintaining the power factor without affecting the electronic transport, resulting in giving rise to the increase in ZT up to 0.39 at 1,000 K.We found that the two-dimensional electron gas (2DEG) formed at the interface of TiO_2/SrTiO_3 exhibit giant Seebeck coefficient which is about 5 times as large as that of a bulk single crystal. We then further succeeded in fabricating the superlattices composed of undoped STO and Nb-doped STO and verified that one unit-cell layer of Nb-doped STO exhibits 4.4 times as large Seebeck coefficient as a bulk single crystal. The ZT at room temperature estimated by taking thermal conductivity of a single crystal was 2.4 which is the world record for thermoelectric energy conversion.