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

单一crystals of homologous phase in the zno - in_2_3 with layer structures were successfully growna flux method这是肯定的，the in-plane electrical conductivity is two orders of magnitude largerY-doped单面crystal was found to show the in-plane conductivity -plane conductivitysimilar to that of textured ceramic，这是一个完整的semi-quantitatively ZT of this system would be ultimately achieved tobe ~ 0.5.We have succeeded in preparing high-quality epitaxial thin films of Na <0.8> cool_2，which further enabled us to synthesize humidity-stable sr_xcool_2 thin films andna__2 / 1.3 h_2o exhibiting superconductivity below 4k . We also succeeded in synthesizingepitaxial thin films of ca_3 co_4o_9 whose thermoelectric properties are comparable to those of abulk single crystal.We have experimentally confirmed that the maximum ZT of heavily sb -doped srtio_3could be 0.37 at 1,000 K. In order to further improve the conversion efficiency，ions, whose ionic radius is similar to Sr^<2+>，were successfully substituted for Sr ions to reduce thermal conductivity while maintaining thepower factor without affecting the electronic transportresulting in giving rise to the increase in ZT up to 0.39 at 1,000 K.We发现thetwo-dimensional electron gas (2deg) formed at the interface of tio_2 / srtio_3 exhibit giant Seebeckcoefficient which is about 5 times as large as that of a bulk single crystal. We then furthersucceeded in fabricating the superlattices composed of undoped STO and Nb-doped STO and verifiedthat one unit-cell layer of Nb-doped STO exhibits 4.4 times as large Seebeck coefficient as a bulkThe ZT at room temperature estimated by taking thermal conductivity of a single . The ZT at room temperature estimated by taking thermal conductivitycrystal was 2.4 which is the world record for thermoelectric energy conversion。

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.