A careful and wide comparison between Al and Ga as substitutional dopants in the ZnO wurtzite structure is presented. Both cations behave as n-type dopants and their inclusion improves the optical and electrical properties of the ZnO matrix, making it more transparent in the visible range and rising up its electrical conductivity. However, the same dopant/Zn ratio leads to a very different doping efficiency when comparing Al and Ga, being the Ga cation a more effective dopant of the ZnO film. The measured differences between Al-and Ga-doped films are explained with the hypothesis that different quantities of these dopant cations are able to enter substitutionally in the ZnO matrix. Ga cations seem to behave as perfect substitutional dopants, while Al cation might occupy either substitutional or interstitial sites. Moreover, the subsequent charge balance after doping appear to be related with the formation of different intrinsic defects that depends on the dopant cation. The knowledge of the doped-ZnO films microstructure is a crucial step to optimize the deposition of transparent conducting electrodes for solar cells, displays, and other photoelectronic devices. V
The magnetic properties of LiM0.5Mn1.5O4 (M=Ni and Cu) spinels, materials of interest as electrodes for Li-ion batteries, have been studied and interpreted with the help of the first-principles calculation method. The magnetic susceptibility of the Ni compound, that behaves virtually as stoichiometric normal spinel, is consistent with the well-established magnetic model of the spinel structure that leads to ferrimagnetism. However, the Cu spinel was oxygen deficient and showed significant divergences from this model. The ferromagnetic component of this spinel was dependent on the calcining temperature and was smaller to that predicted by the magnetic model. The special crystal structure of the spinel, namely, oxygen deficiency and increased occupancy of the tetrahedral sites by Cu ions, satisfactorily explains the more complex magnetic behavior observed, further supported by the results of the first-principles electronic structure computations.
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