Navegando por Assunto "Cristais dopados"

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Acesso aberto (Open Access)
Crescimento e caracterização dos cristais de sulfato de níquel hexahidratado dopados com íons [MnH2O]2+ e com sulfato de magnésio heptahidratado
(Universidade Federal do Pará, 2011) FERREIRA JÚNIOR, Messias de Nazaré Guimarães; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490
In this work, manganese ions doped nickel sulphate crystals (NSH:Mn) and magnesium ion doped nickel sulphate crystals (NMgSH) were grown and later characterized by X-ray diffraction and Raman spectroscopy techniques. The results obtained showed that the doped crystals possess a structure very similar to that of the pure nickel sulphate crystal (NSH), with an anisotropic deformation in the unit cell dimensions compared to the pure crystal, undergoing expansion in unit. The aim of the present study was to grow two new single crystals of good optical quality to be used as optical bandpass filters. Nickel sulfate hexahydrate (NHS) crystals are known to possess an optical transmission spectrum which has attracted much attention because it presents two regions with high transmission efficiency of approximately 80%, the first region being between 200 and 350 nm and the second between 400 and 600 nm, and a high absorption efficiency in other regions of the UV-VIS spectrum. A light transmission spectrum with these characteristics is similar to an optical filter. Termogravimetric (TGA) analyses were carried out for pure and doped crystals. The obtained decomposition temperature of NSH was found to be 73 °C while that NSH: Mn and NMgSH crystals present values of 82 ° C and 86 C respectively. As can be easily perceived, the thermal stability of crystals with Mn or Mg ions in their structures is significantly higher. The transmission band between 200 and 350 nm in the optical spectrum of NSH was found to be narrower in the transmission spectrum of the doped crystal thus restricting the region of the spectrum known as UVA.
Acesso aberto (Open Access)
Difração de policristais e difração múltipla de raios X para o estudo da influência dos íons Mn+2, Mg+2 e Cu+2 nas estruturas cristalinas da L asparagina monohidratada e do sulfato de níquel hexahidratado
(Universidade Federal do Pará, 2012) MELO, Geraldo Souza de; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490
In this work we accomplished a study about the influence of doping Mn+2, Mg+2 and Cu+2 in the crystal structures of crystals of nickel sulfate hexahydrate (NSH) and L Asparagine Monohydrate (LAM). The introduction of dopants in a crystal lattice must change its physical properties or growth habit. These changes must promote the technological applications of these crystals in many areas like medicine, agriculture, optics and electronics. The NSH crystals were grown by the slow evaporation method of the solvent and doped with ions of Mn+2 and Mg+2, resulting in crystals of good quality. We measures method of X-ray diffraction of the pure crystals and polycrystalline doped and from the results obtained we refinements, using the method of Rietiveld where was observed that the same crystal structure doped showed the same tetragonal and space group that the pure crystal, having a little change in their lattice parameters and volume of its unit cells. We observed that the introduction of dopants caused changes in the lengths of the links and the angles between the nickel and oxygen atoms, this may explain why the temperature of dehydration crystals NSH:Mn and NSH:Mg is bigger than that of pure NSH. We use the X-ray Diffraction Multiple technique with synchrotron radiation in differents energies on the workstation XRD1, of the National Synchrotron Light Laboratory (LNLS) in order to identify possible changes in the structures of doped crystals of nickel sulphate and L Asparagine. The Renninger diagrams show changes in the intensity, profile and position of the secondary peaks of doped crystals caused by the introduction of dopants. The crystals were grown L Asparagine monohydrate by the method of slow solvent evaporation, and doped with ions of Cu+2. The diffraction measurements showed that the doped crystal has the same orthorhombic structure that the pure crystal. Our results indicate that the incorporation mechanisms of the Cu+2 ions in the crystal lattice of Asparagine Monohydrate L occur in interstitial form. Changes were detected in intensity as well as in the positions and profile diagrams Renninger secondary peaks in the crystal doped.
Acesso aberto (Open Access)
Estudo de propriedades estruturais e de piezeletricidade nos cristais de ADP e KDP puros e dopados com íons Ni2+ e Mn3+ com DMRX utilizando radiação síncrotron
(Universidade Federal do Pará, 2010-08-31) GOMES, Eduardo José de Lima; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490
The X-ray multiple diffraction using synchrotron radiation has been applied to study transition metal cátions Mn 3+ and Ni 2+ incorporated into Ammonium Diydrogen Phosphate (ADP) Crystal lattice and potassium dihydrogen phosphate (KDP). The results shows that regarding peak positions and number of peaks all the profilets look almost identical. This fact alone tells us that the unit cell parameters and the crystal symmetry are practically the same regardless of the incorporation of Mn 3+ and Ni 2+ cations. Accurate calculation of the unit-cell parameters revels that the lattices lattices parameters a = b increase and lattices parameters c decrease following Ni 2+ and Mn 3+ incorporation. In the measurements for the two wavelengths ADP:Mn crystal exhibit asymmetric peak profiles and no extra peak appears in the whole Mn 3+ doped RS. On the other hand, in the ADP:Ni measurements one can clearly observe: (i) suppression of the intensity profile asymmetry in secondary peaks for the Ni 2+ doped RS (below l Ni 2+ Kedge) and also, (ii) marked asymmetry inversion (above l Ni 2+ Kedge), for example the peak (5-12) / (-112) which represents a four beam case. These results indicate that synchrotron radiation RS is a high resolution probe to be used in the impurity incorporation in the ADP lattice. Moreover we have investigated ADP:Mn, KDP:Mn and KDP:Ni crystals using X-ray diffraction at room temperature. The results of the measurements of 440 and 066 reflections allow obtaining the d 36 and d 25 coefficients. We reported on the experimental verification based on X-ray measurements, the d 36 piezoelectric coefficients increased with doping of the Mn and Ni 2+ in the KDP and in ADP crystals.