Electrical transport and thermoelectric properties of Ni-doped perovskite-type YCo_1-xNi_xO₃ (0≤ x ≤0.07) prepared by sol-gel process

Electrical transport and thermoelectric properties of Ni-doped YCo_1-xNi_xO₃ (0≤ x ≤0.07), prepared by using sol-gel process, are investigated in a temperature range from 100 to 780 K. The results show that with the increase of Ni doping content, the values of DC resistivity of YCo_1-xNi_xO₃ decrease, but carrier concentration increases. The temperature dependences of the resistivity for YCo_1-xNi_xO₃ are found to follow a relation of lnρ ∝ 1/T in a low-temperature rang (LTR) (T<～304 K for x=0; ～ 230 K < T <～500 K for x=0.02, 0.05, and 0.07) and high-temperature range (HTR) (T > ～ 655 K for all compounds), respectively. The estimated apparent activation energies for conduction E_a1 in LRT and E_a2 in HTR are both found to decrease monotonically with doping content increasing. At very low temperatures (T < ～ 230 K), Mott's law is observed for YCo_1-xNi_xO₃ (x ≥ 0.02), indicating that considerable localized states form in the heavy doping compounds. Although the Seebeck coefficient of the compound decreases after Ni doping, the power factor of YCo_1-xNi_xO₃ is enhanced remarkably in a temperature range from 300 to 740 K, i.e., a 6-fold increase is achieved at 500 K for YCo_0.98Ni_0.02O₃, indicating that the high-temperature thermoelectric property of YCoO₃ can be improved by partial substitution of Ni for Co.