O plÃsmon da regiÃo de recobrimento da ligaÃÃo quÃmica como ferramenta para caracterizaÃÃo de materiais

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Important issues can be raised about the possibility of relations between macroscopic properties of materials and concepts, introduced recently, of the chemical bond overlap polarizability (PR) and the concept of ionic specific valence (VIE). A proposal in which the overlap region of chemical bond is considered as a âplasmon‐likeâ charge distribution â Chemical Bond Overlap Plasmon (PRR) â has raised the question on the possibility of absorption and inelastic scattering of radiation in the overlap region. The main objective of this study is to explore the physical meanings of the overlap region plasmon and polarizability concepts in case of the solid state. It also aims to use the concepts of overlap region polarizability and plasmon for characterization of materials in solid state, in terms of their covalency. The analyzed systems was the alkali halides MX (where M = Li, Na, K e X = F, Cl, Br), α phase of aluminum oxide, α‐quartz phase of silicon oxide, cassiterite phase of tin oxide. These systems were chosen because they represent fundamental classes of compounds in solid state and presents available experimental results in literature. The results show that the overlap polarizability is consistent with the chemical bond polarizability decomposition (αPR <αmol ). Besides, αPR presents a strong linear correlation with the molar polarizability αmol (R2 = 0.973). The adjusted equation makes possible the use of αPR as a tool for provide the polarizability of entire metarial. An excellent correlation (R2 = 0.959) was found for the exponential adjust between αPR and the material bandgap energy Eg. The adjusted equation makes possible the characterization of materials with respect to their covalency, given the Eg. It was concluded that the plÃsmon can be physically measured. Moreover, the obtained energies for this oscillator are in the range of 5 â 20 eV, region where the effects of excitons, collective plasmons and the firsts inter and intraband transitions are observed. The PRR can be used for the characterization of the optical properties in range of 5 â 20 eV. The chemical bond overlap plasmon effect may be related to some smooth structures in the spectra of light absorption and energy loss‐function, and may be an alternative way to interpret the peaks attributed to the exciton effects in halogens halides

ASSUNTO(S)

quimica ligaÃÃo quÃmica chemical bond polarizability polarizabilidade overlap region covalency regiÃo de recobrimento covalÃncia theoretical chemistry quÃmica teÃrica

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