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

通过自组装织构提高层状氧化物热电材料的能量转换效率

基本信息

批准号：
14103008
负责人：
KOUMOTO Kunihito
金额：
$ 70.72万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (S)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2006
项目状态：
已结题

项目摘要

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.

采用助熔剂法成功生长了层状结构的ZnO-In_2O_3同系单晶，并证实其面内电导率比面外电导率大两个数量级。发现Y掺杂单晶表现出与织构陶瓷相似的面内电导率，并半定量验证了该体系的ZT最终可达到〜0.5。我们成功制备了高质量的Na_<0.8>CoO_2外延薄膜，这进一步使我们能够合成湿度稳定的Sr_xCoO_2薄膜和 Na_<0.3>CoO_2·1.3H_2O在4 K以下表现出超导性。我们还成功合成了Ca_3Co_4O_9外延薄膜，其热电性能与块状单晶相当。我们通过实验证实，重Nb掺杂的SrTiO_3（STO）在1,000 K时的最大ZT可以达到0.37。为了进一步提高转换效率，成功地用离子半径与Sr^<2+>相近的Eu^<2+>离子替代Sr^<2+>离子，以降低热导率，同时保持功率因数而不影响电子输运，导致ZT在1,000 K时增加高达0.39。我们发现在Eu^<2+>离子的界面处形成了二维电子气（2DEG）。 TiO_2/SrTiO_3表现出巨大的塞贝克系数，约为块状单晶的5倍。然后，我们进一步成功地制造了由未掺杂的 STO 和掺铌的 STO 组成的超晶格，并验证了掺铌的 STO 的一层晶胞的塞贝克系数是块状单晶的 4.4 倍。通过计算单晶的导热系数估算出的室温ZT为2.4，这是热电能量转换的世界纪录。