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The fabrication of a superhydrophobic carbon nanofiber (CNF) on various substrates via a two-step process is reported, eliminating the need for multiple pre- and post-treatments with toxic chemicals.

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In the present work, we report the experimental thermopower (α) data for ZnV2O4 in the high temperature range 300-600 K. The values of α are found to be ∼184 and ∼126 µV/K 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 structures 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 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 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 ZnV2O4 is ∼0.3 in the temperature range 900-1400 K. It suggests that by appropriate amount of p-type doping, this compound can be a good thermoelectric material in high temperature region. 71.15.Mb, 74.25.Fy

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Here we investigate the temperature evolution of the structural parameters of a potential magnetoelectric material, MnTiO3. The experimental results reveal interesting temperature dependence of the c/a ratio and the Mn-O bonds which can be divided into three regions. In region I (300 K to 200 K), the above parameters are seen to decrease with decrease in temperature due to thermal effect. In the region II (200 K to 95 K), the decrement in the structural parameters are reduced due the competing intra layer antiferromagnetic interaction setting in ∼ 200 K. The c/a ratio are seen to display a minima around 140 K. Below 140 K, the short Mn-O bonds increase suggesting the onset of inter layer antiferromagnetic interaction ∼ 100 K. In region III (95 K to 23 K), the antiferromagnetic interaction is fully established. The behaviour of the calculated Mn-O bonds based on first principle calculations are in line with the experimental results. This study demonstrates the importance of spin lattice coupling in understanding the magnetic properties of the compound which is expected to be helpful in revealing the origin of magnetically induced ferroelectricity.

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We investigate room temperature core level and valence band spectra of BaBiO 3 using x-ray photoemission spectroscopy and band structure calculations. The features in the valence band spectrum were studied using density functional theory (DFT) under local density approximation (LDA) and Tran Blaha modified Becke Johnson (TB mBJ) exchange potential. The calculations were performed for three different structural parameters; monoclinic, cubic and monoclinic (M ). Our results of the core level spectrum and DFT calculations rule out charge disproportionation of the Bi ions. The valence band spectrum displays gap at the Fermi edge and fine structures in the region close to the Fermi edge. The DFT calculation under TB mBJ for the monoclinic structure is able to generate gap and match the energy positions of the fine structure in a better way. Our calculation results show that there are holes in the O 2 p states and unequal transfer of electrons to the states of the Bi ions. Such mechanism could lead to bond disproportionation and its association with the fine structures in the valence band. The current results reveal the significance of strong link between the lattice distortion and electronic structure and hence to its physical properties.