Understanding the thermoelectric properties of LaCoO3 compound

We present the thermoelectric (TE) properties of LaCoO3 compound in the temperature range 300-600 K. The experimental value of Seebeck coefficient (alpha) at 300 K is found to be similar to 635 mu V/K. The value of alpha decreases continuously with increase in temperature and reaches to similar to 46 mu V/K at similar to 600 K. The electronic and TE properties of the compound have also been investigated by combining the ab initio electronic structures and Boltzmann transport calculations. LSDA plus Hubbard U (U = 2.75 eV) calculation on low spin configuration of the compound gives an energy gap of similar to 0.5 eV, which is close to the experimentally reported energy gap. The effective mass of holes (m(h)*) at Gamma point is nearly two times larger than the value of effective mass of electrons (m(e)*) at FB point along the L and T directions, whereas the m(e)* at FB point along the Gamma direction is nearly eight times larger than the value of m(h)* at Gamma point along the FB direction. The large effective mass at FB point along the Gamma direction suggests that the TE property of this compound is mainly decided by the effective mass of the charge carriers in this direction. The calculated temperature dependent values of a are in fairly good agreement with experimental data in the temperature range 300-360 K, and above this temperature slight deviation is observed. The value of power factor (PF) for n-type is similar to 1.3 times larger the value of p-type doped compound at 1100 K. The value of figure-of-merit (ZT) for n-type doped compound is obtained similar to 0.35 in the temperature range 600-1100 K, which suggests that with appropriate n-type doping this compound can be used as a good TE material in the high temperature region.