Anisotropic electrical and thermal conductivity in Bi2AE2Co2O8+δ [AE=Ca, Sr1–xBax (x=0.0, 0.25, 0.5, 0.75, 1.0)] single crystals.

Bi₂AE₂Co₂O_8+δ (AE represents alkaline earth), constructed by stacking of rock-salt Bi₂AE₂O₄ and triangle CoO₂ layers alternatively along c-axis, is one of promising thermoelectric oxides. The most impressive feature of Bi₂AE₂Co₂O_8+δ, as reported previously, is their electrical conductivity mainly lying along CoO₂ plane, adjusting Bi₂AE₂O₄ layer simultaneously manipulates both thermal conductivity and electrical conductivity. It in turn optimizes thermoelectric performance of these materials. In this work, we characterize the anisotropic thermal and electrical conductivity along both ab-plane and c-direction of Bi₂AE₂Co₂O_8+δ (AE=Ca, Sr, Ba, Sr_1–xBa_x) single crystals. The results substantiate that isovalence replacement in Bi₂AE₂Co₂O_8+δ remarkably modifies their electrical property along ab-plane; while their thermal conductivity along ab-plane only has a slightly difference. At the same time, both the electrical conductivity and thermal conductivity along c-axis of these materials also have dramatic changes. Certainly, the electrical resistance along c-axis is too high to be used as thermoelectric applications. These results suggest that adjusting nano-block Bi₂AE₂O₄ layer in Bi₂AE₂Co₂O_8+δ cannot modify the thermal conductivity along high electrical conductivity plane (ab-plane here). The evolution of electrical property is discussed by Anderson localization and electron-electron interaction U. And the modification of thermal conductivity along c-axis is attributed to the microstructure difference. This work sheds more light on the manipulation of the thermal and electrical conductivity in the layered thermoelectric materials. [ABSTRACT FROM AUTHOR]