Development of new-type cobalt oxide thermoelectric materials

Single phase cobalt oxide thermoelectric materials, A(x)CoO(2) with A=Na,Sr, Ca and Ba, [A'2CoO3](z)[CoO2] with A'=Ca,Sr(349-phase), z=0.62 and [Ca-2(Co1-y,Cu-y,)(2)O-4](z)[CoO2] with y=0.33 are synthesized successfully by the ion-exchange method or solid state reaction method. Seebeck coefficient, electric resistivity and magnetization of these oxides are measured in the temperature range from 4K to 300K. These cobalt oxides show p-type conductivity and relatively high positive Seebeck coefficient, i.e., about 120 muV/K or above at 300K. The electric resistivity of sintered samples has been measured at the level of 10 mOmegacm at 300K. New nomenclature, the naming system, of modulated layered cobalt oxide thermoelectric materials, e.g., the latter two ones, is proposed according to the numbers of stacking cation layers, namely Co-121 for [Ca2CoO3](0.62)[CoO2], Co(Cu)-221 for [Ca-2(Co1-yCuy)(2)O-4](z)[CoO2] and Bi-221 for [Bi0.87SrO2](2)[CoO2](1.82), respectively. The top letter is the cation(s) sitting in the rocksalt layer(s). The 1(st), 2(nd) and 3(rd) digits indicate the numbers of the rocksalt-type metal-oxygen layer(s), alkali earth metal-oxygen layer(s) and conducting triangle cobalt oxygen layer(s) in a unit cell, respectively.