Papers by Keyword: Band Structures

Abstract: Thermoelectric materials has made a great potential in sustainable energy industries, which enable the energy conversion from heat to electricity. The band structure and thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ have been investigated. The bulk pellets were prepared from analytical grade ZnO, NiO and Fe₂O₃ powder using solid-state method. It was possible to obtain high thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ by controlling the ratios of dopants and the sintering temperature. XRD analysis showed that the fabricated samples have a single phase formation of cubic spinel structure. The thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ pellets improved with increasing Ni. The electrical conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ pellets decreased with increasing Ni content. The electrical conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ (x = 0.0) is (0.515 x10^-3 Scm^-1). The band structure shows that Zn_xCu_1-xFe₂O₄ is an indirect band gap material with the valence band maximum (VBM) at M and conduction band minimum (CBM) at A. The band gap of Ni_(x)Zn_(1-x)Fe₂O₄ increased with increasing Ni content. The increasing band gap correlated with the lower electrical conductivity. The thermal conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ pellets decreased with increasing Ni content. The presence of Ni served to decrease thermal conductivity by 8 Wm^-1K^-1 over pure samples. The magnitude of the Seebeck coefficient for Ni_(x)Zn_(1-x)Fe₂O₄ pellets increased with increasing amounts of Ni. The figure of merit for Ni_(x)Zn_(1-x)Fe₂O₄ pellets and thin films was improved by increasing Ni due to its high Seebeck coefficient and low thermal conductivity.

Abstract: The calculated results based on the density functional theory are employed to simulate the nonlinear optical properties of a new compound of Ba₇Sn₅S₁₅ (BSS). The frequency (ω=eV/ħ) dependent SHG tensor components of the BSS are calculated from 0.0 to 2.0 eV energy range. The calculated components d₃₁(20.3 pm/V) and d₃₃(18.8 pm/V) are close to the experimental value of of 19.5 pm/V at a wavelength of 2.10 μm. The SHG conversion efficiency and the figure of merit of BSS material are about two fold as compared with those of AgGaS₂ material. The charge transfers within the (Sn₂S₃) and (SnS₄) polyhedrons lead to the most contribution to SHG response, and the polarity superposition of the [Sn₂S₃]^2- groups will strengthen the crystal polarity and result in a large SHG response in a BSS material.

Abstract: The Tetrahedrite’s family constitutes a complete solid-solution series, and is among the most frequent complex sulfides in Nature. This kind of structure can be generically expressed by the composition, Cu₁₂Sb₄S₁₃. We have calculated the electronic band structure of Cu₁₂Sb₄S₁₃ and Ag₆Cu₆Sb₄S₁₃ (with band gaps of 1.24 and 1.20 eV, respectively) to demonstrate that different elements occupying certain sites of the crystal structure will make a difference in what concerns the conduction process in Tetrahedrites. We will use this effect and ab initio calculations to show that the electronic properties of these compounds make them promising candidates as solar cells photovoltaic materials since not only they possess a direct band gap but their energy falls within the range of energies of photovoltaics. Moreover, we can optimize these properties by doping and substituting ions furthermore. Mechanical properties were also calculated for both compounds and will be compared.