The research on ordered perovskite-type oxide Cd_3TeO_6 with the aim of making new thermoelectric materials

采用引入氧空位和以In、Bi、La取代Cd两种方法，将电子掺杂到具有1:1有序钙钛矿型结构的Cd_3TeO_6中。两种方法均可使多晶样品变成金属导体，而第二种方法则可获得具有金属导电性的单晶。单晶铟取代样品的电阻率和热电功率分别为0.6 mΩ cm和-50 μV/K，功率因数为4×10^<-4> W K^<-2> m^<-1>，是非过渡金属氧化物中最高的。电子掺杂Cd_3TeO_6良好的热电性能来源于其优异的导电性。虽然目前导电性能良好的原因尚不清楚，但可以认为电子掺杂Cd_3TeO_6的结构特征提供了Cd_3TeO_6特殊的电特性。有序钙钛矿氧化物Cd_3TeO_6的结构是强变形的（单…更斜，P2_1/n），镉离子在A位和B位的Cd-O距离相似。因此，在电子掺杂的Cd_3TeO_6中，引入到Cd^<2+>和Te^<6+>空5s轨道上的电子不仅可以与b位阳离子的5s轨道重叠，还可以与a位镉离子的5s轨道重叠，从而在结构中移动。Cd_3TeO_6特有的导电网络可能与该材料的高导电性有关。综上所述，我们还通过用In^<3+>取代Cd^<2+>离子成功地修饰了多晶和单晶Cd_3TeO_6样品。多晶样品的电子掺杂也可以通过引入氧空位来实现。对热电性质的研究表明，单晶Cd_<3-x>In_xTeO_6的热电优值Z （Z=S^2ρ^<-1>κ^<-1>）在室温下约为1.0×10^<-4> K^<-1>。电子掺杂的Cd_3TeO_6是一种很有前途的n型热电材料。少

Electron doping into Cd_3TeO_6 with a 1:1 ordered perovskite-type structure was carried out by two methods : the introduction of oxygen vacancies and the atomic substitution of In, Bi and La for Cd. Both methods turned polycrystalline samples into metallic conductors while single crystals with metallic conductivity were obtained by the second method. The resistivity and thermoelectric power of the single-crystal indium-substituted sample were 0.6 mΩ cm and -50 μV/K, respectively, giving a power factor of 4×10^<-4> W K^<-2> m^<-1>, which is the highest among non-transition metal oxides. The good thermoelectric performance of the electron-doped Cd_3TeO_6 derives from its excellent electrical conductivity. Though the reason for the good conductivity is not clear at present, the structural feature of the electron-doped Cd_3TeO_6 may be considered to provide the special electric characteristics of Cd_3TeO_6. The structure of the ordered perovskite oxide Cd_3TeO_6 is strongly deformed (monoc … More linic, P2_1/n), and the Cd-O distances are similar for the cadmium ions in both the A and B sites. Therefore, in the electron-doped Cd_3TeO_6, electrons introduced into the empty 5s orbitals of Cd^<2+> and Te^<6+> can move in the structure through the overlap of the 2p orbitals of the oxide ions not only with the 5s orbitals of the the B-site cations but also with the 5s orbitals of the A-site cadmium ions. This conducting network unique to Cd_3TeO_6 may be related to the high conductivity of this material.In conclusion, we successfully modified the polycrystalline and single-crystal Cd_3TeO_6 samples also by substituting In^<3+> cations for Cd^<2+> ions. The electron doping of the polycrystalline samples could be attained also by introducting oxygen vacancies. This investigation of thermoelectric properties has revealed that the thermoelectric figure-of-merit Z (Z=S^2ρ^<-1>κ^<-1>) of a single crystal, Cd_<3-x>In_xTeO_6, is approximately 1.0×10^<-4> K^<-1> at room temperature. The electron-doped Cd_3TeO_6 is a promising n-type thermoelectric material. Less