No abstract

Transition metal oxides have been attracted much attention in thermoelectric community from the last few decades. In the present work, we have synthesized LaNiO3 by a simple solution combustion process. To analyze the crystal structure and structural parameters we have used Rietveld refinement method wherein FullProf software is employed. The room temperature x-ray diffraction indicates the rhombohedral structure with space group R 3 c (No. 167). The refined values of lattice parameters are a = b = c = 5.4071 Å. Temperature dependent Seebeck coefficient (S) of this compound has been investigated by using experimental and computational tools. The measurement of S is conducted in the temperature range 300-620 K. The measured values of S in the entire temperature range have negative sign that indicates n-type character of the compound. The value of S is found to be ∼ -8 µV/K at 300 K and at 620 K this value is ∼ -12 µV/K. The electronic structure calculation is carried out using DFT+U method due to having strong correlation in LaNiO3. The calculation predicts the metallic ground state of the compound. Temperature dependent S is calculated using BoltzTraP package and compared with experiment. The best matching between experimental and calculated values of S is observed when self-interaction correction is employed as double counting correction in spin-polarized DFT + U (= 1 eV) calculation. Based on the computational results maximum power factors are also calculated for p-type and n-type doping of this compound.

We report the thermoelectric (TE) properties of Na0.74Co0.95Nb0.05O2 in the temperature range 300 − 1200 K, as a potential candidate for p-type thermoelectric material. The experimental values of Seebeck coefficient (S) are ∼ 82 − 121 µV/K measured in the temperature range 300 − 620 K. The positive values of S in the entire temperature range indicates p-type behaviour of the compound. At 300 K the experimental value of thermal conductivity (κ) is ∼ 1.88 W/m-K that increases up to ∼ 420 K, then decreases till 620 K with corresponding value ∼ 1.86 W/m-K. To understand the experimentally observed transport properties, we have calculated S and ρ of this compound. Then, based on theoretical understanding, we have estimated figure-of-merit (ZT) up to 1200 K by using calculated S and ρ values with extrapolated experimental κ. The value of ZT is found to be ∼ 0.03 at 300 K, whereas, the highest value is observed as ∼ 1.7 at 1200 K. Finally, we have calculated the efficiency (η) by keeping the cold end temperature (Tc) fixed at 500 K and varying hot end temperature (T h ) from 500 to 1200 K, respectively. The maximum value of η is found to be ∼ 8 %, when Tc and T h are fixed at 500 and 1200 K, respectively. This result suggests that Na0.74Co0.95Nb0.05O2 compound can be used as a p-leg for making high temperature TE generator (TEG).