We investigate the spin state of $\mathrm{La}\mathrm{Co}{\mathrm{O}}_3$ using state-of-the-art photoemission spectroscopy and ab initio band structure calculations. The $\mathrm{GGA}+U$ calculations provide a good description of the ground state for the experimentally estimated value of electron correlation strength $U$. In addition to the correlation effect, spin-orbit interaction is observed to play a significant role in the case of intermediate spin and high spin configurations. The comparison of the calculated $\mathrm{Co}3d$ and $\mathrm{O}2p$ partial density of states with the experimental valence band spectra indicates that at room temperature, Co has dominant intermediate spin state configuration and that the contribution from high spin configuration may not be significant at this temperature. The line shape of the $\mathrm{La}5p$ and $\mathrm{O}2s$ core level spectra could be reproduced well within these ab initio calculations.

We present the thermoelectric (TE) properties of LaCoO compound in the temperature range 300–600 K. The experimental value of Seebeck coefficient ( ) at 300 K is found to be V/K. The value of decreases continuously with increase in temperature and reaches to V/K at 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 ( eV) calculation on low spin configuration of the compound gives an energy gap of eV, which is close to the experimentally reported energy gap. The effective mass of holes ( ) at point is nearly two times larger than the value of effective mass of electrons ( ) at FB point along the L and T directions, whereas the at FB point along the direction is nearly eight times larger than the value of at point along the FB direction. The large effective mass at FB point along the 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 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 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 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.

In the present work, we report the experimental thermopower ( α ) data for ZnV ₂ O ₄ in the high temperature range 300–600 K. The values of α are found to be ∼184 and ∼126 μ V K ⁻¹ at ∼300 and ∼600 K, respectively. The temperature dependent behavior of α is almost linear in the measured temperature range. In order to understand the large and positive α values observed in this compound, we have also investigated the electronic and thermoelectric properties by combining the ab initio electronic structure calculations with Boltzmann transport theory. Within the local spin density approximation plus Hubbard U, the anti-ferromagnetic ground state calculation gives an energy gap ∼0.33 eV for U = 3.7 eV, which is in accordance with the experimental results. The effective mass for holes in the valence band is found nearly four times that of electrons in the conduction band. The large effective mass of holes are mainly responsible for the observed positive and large α value in this compound. There is reasonably good matching between calculated and experimental α value in the temperature range 300–410 K. The power factor calculation shows that thermoelectric properties in the high temperature region can be enhanced by tuning the sample synthesis conditions and suitable doping. The estimated value of figure-of-merit , ZT , for p-type doped ZnV ₂ O ₄ is ∼0.3 in the temperature range 900–1400 K. It suggests that by an appropriate amount of p-type doping, this compound can be a good thermoelectric material in the high temperature region.

We have investigated the electronic and magnetic properties of the pulsed laser deposited epitaxial thin films of undoped and Fe doped (4 at. %) anatase TiO2−d by photoemission, magnetization measurements, and ab-initio band structure calculations. These films show room temperature magnetic ordering. It is observed that Fe ions hybridize with the oxygen vacancy induced Ti3+ defect states. Our study reveals the formation of local magnetic moment at Ti and Fe sites to be responsible for magnetic ordering. A finite density of states at the Fermi level in both undoped and Fe doped films is also observed, suggesting their degenerate semiconducting nature.

Accurate measurement of efficiency for a thermoelectric generator (TEG) is of great importance for materials research and development. Approximately all the parameters of a thermoelectric material (TEM) are temperature dependent, and so we cannot directly apply the η_max formula for efficiency calculation in the large temperature range. In this work, we have calculated TEG efficiency, and we study the suitability of different TEMs like Bi₂Te₃, Sb₂Te₃, PbTe, TAGS ((AgSbTe₂)_0.15(GeTe)_0.85), CeFe₄Sb₁₂, SiGe, and TiO_1.1 in the estimation of TEG efficiency. The efficiency of TEG made up of Bi₂Te₃ or Sb₂Te₃ gives ∼7% in the temperature range of 310 K–500 K. PbTe or TAGS or CeFe₄Sb₁₂ generates ∼6% in the temperature range of 500 K–900 K and SiGe or TiO_1.1 also have remarkable efficiency in the higher temperature range, i.e., ∼1200 K. The calculated efficiency obtained is close to experimental results. Here, we report the enhancement of efficiency by using the segmented technique for different combinations of the above-mentioned materials. To this end, the proposed values of overall efficiency of TEG by segmenting Bi₂Te₃ and PbTe; Bi₂Te₃ and TAGS; Bi₂Te₃ and CeFe₄Sb₁₂ are 12%, 14%, and 11.88%, respectively, for the temperature range of 310 K–900 K. For automobiles, the efficiency of TEG having fixed exhaust temperature with varying sink temperature is also discussed. For the steel industry and spacecraft applications (up to 1200 K), either segmentation is done by comprising Bi₂Te₃, PbTe and SiGe, or Bi₂Te₃ and TiO_1.1, which yields an efficiency of ∼15.2% and ∼17.2%, respectively. The relative change in efficiency by considering loss at the interface surface is found to be 10.5%. The proposed methodology and results can be treated as a viable option for engineers who are looking to fabricate TEG in real life by using the temperature dependent material's parameters such as thermal conductivity, electrical conductivity, and Seebeck coefficient on which $z\overline{T}$ depends.