Intense and broad photoluminescence at room temperature in structurally disordered Ba[Zr0.25Ti0.75]O-3 powders: An experimental/theoretical correlation

Intense and broad photoluminescence (PL) emission at room temperature was observed on structurally disordered Ba[Zr0.25Ti0.75]O-3 (BZT) powders synthesized by the polymeric precursor method. BZT powders were annealed at 573 K for different times and at 973 K for 2 h in oxygen atmosphere. The single-phase cubic perovskite structure of the powder annealed at 973 K for 2 It was identified by X-ray diffraction and Fourier transform Raman techniques. PL emission increased with the increase of annealing time, which reached its maximum value in the powder annealed at 573 K for 192 h. First principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and disordered models. The theoretical calculations and experimental measurements of Ultraviolet-visible absorption spectroscopy indicate that the presence of intermediary energy levels in the band gap is favorable for the intense and broad PL emission at room temperature in disordered BZT powders. The PL behavior is probably due the existence of a charge gradient on the disordered structure, denoted by means of a charge transfer process from [TiO5]-[ZrO6] or [TiO6]-[ZrO5] clusters to [TiO6]-[ZrO6] clusters. (C) 2008 Elsevier Ltd. All rights reserved.

Leakage current, ferroelectric and structural properties in Pb(1-x)Ba(x)TiO(3) thin films prepared by chemical route

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Photoluminescence in quasi-amorphous Pb0.8X0.2Zr0.53Ti0.47O3 (X = Ca, Sr and Ba) powders: An optical and structural study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Optical and dielectric relaxor behaviour of Ba(Zr0.25Ti0.75)O-3 ceramic explained by means of distorted clusters

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The tadpole of Physalaemus jordanensis Bokermann, 1967 (Anura, Leiuperidae) from Campos do Jordao, Serra da Mantiqueira, Southeastern Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Photoluminescence property of Ba(Zr0.25Ti0.75)O-3 powders prepared by solid state reaction and polymeric precursor method

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structural and dielectric relaxor properties of yttrium-doped Ba(Zr0.25Ti0.75)O-3 ceramics

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Study of phase transition in (Pb,Ba)TiO(3) thin films

Dielectric and Raman scattering experiments were performed on polycrystalline Pb(1-x)Ba(x)TiO(3) thin films (x=0.40 and 0.60) as a function of temperature. The dielectric study on single phase compositions revealed that a diffuse-type phase transition occurred upon transformation of the cubic paraelectric to the tetragonal ferroelectric phase in all thin films, which showed a broadening of the dielectric peak. Diffusivity was found to increase with increasing barium contents in the composition range under study. In addition, the temperature dependence of Raman scattering spectra was investigated through the ferroelectric phase transition. The temperature dependence of the phonon frequencies was used to characterize the phase transitions. Raman modes persisted above the tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted as a breakdown of the local cubic symmetry by chemical disorder. The lack of a well-defined transition temperature and the presence of broadbands in some temperature intervals above the paraferroelectric phase transition temperature suggest a diffuse-type phase transition. (C) 2008 American Institute of Physics.

Biologia populacional de Pareiorhina rudolphi (Loricariidae, Hypostominae) na microbacia do Ribeirão Grande, serra da Mantiqueira oriental, Estado de São Paulo

Pareiorhina rudolphi was sampled in streams of the Ribeirao Grande system, eastern Serra da Mantiqueira (22[degree]47[minute]08[second]S, 45[degree]28[minute]17[second] W). Samplings were carried out using an electrofishing device, during the months of July/2001, October/2001, February/2002 and April/2002. Sex-ratio diverged significantly from the expected 1: 1 ratio([chi]2 = 6.53; p < 0.05), standing at 1.6:1 (female: male). The spawning period for Pareiorhina rudolphi lasts from spring to summer, with, the highest observed, in October and February by the gonadosomantic index and the relative condition factor coincided with the spawning period. The length at sexual maturity of P. rudolphi is about 4.45 cm for both sexes. The absolute fecundity was low, and ranged from 4 to 11 oocytes. The periphyton was used as a direct food source by the species, which remain attached to the substrate with their large circular lips, and use their conspicuous Slightly Yellowish teeth to graze the periphyton. The growth parameters, natural mortality rate and survival rate for P, rudolphi were respectively: K = 0.35 year-1, L[infinity] = 7.2 cm, tmax = 8.6 years, M = 1.1 year-1, S = 33%. The characteristics presented by P. rudolphi occur in the environment function of a population adjustment, and not of species abundance.

Aspectos da reprodução e alimentação de Neoplecostomus microps (Loricariidae, Neoplecostominae) na microbacia do Ribeirão Grande, serra da Mantiqueira oriental (Estado de São Paulo)

Reproduction and feeding aspects of Neoplecostomus microps (Loricariidae, Neoplecostominae) in the Ribeirao Grande system, eastern Serra da Mantiqueira (São Paulo State). The Ribeirao Grande system is located in the slope of the Serra da Mantiqueira and is surrounded by Atlantic forest. Eight sites were surveyed in the Ribeirao Grande system, during the winter (July 2001), spring (October 2001), summer (February 2002) and fall (April 2002). Samples were made with an electrofishing device. Gonad maturation, levels of stomach fullness and fat content were analyzed and their distributions reported in an annual cycle. Neoplecostomus microps has a spawning in the spring through to summer. The size at sexual maturity is about 5.9 cm total length for males and 6.9 cm for females. The high values in October and February by the gonadosomatic index and the relative condition factor coincided with the spawning period. In the diet of N. microps were found Diptera larvae (Simulium, Chironomus), Plecoptera nymphs and Coleoptera aquatic Larvae (Psephenus). The increased feeding from summer to fall provided fat accumulation. During subsequent seasons, fish may utilize visceral fat reserves for maintenance and reproduction. The reproductive pattern and feeding are interpreted as being an adaptation with respect to temporal and spatial variation and food availability.

Biologia populacional de Imparfinis minutus (Siluriformes, Heptapteridae) na microbacia do Ribeirão Grande, serra da Mantiqueira oriental, Estado de São Paulo

Populational biology of Imparfinis minutus (Siluriformes, Heptapteridae) in the Ribeirao Grande microbasin, eastern Mantiqueira mountain range, São Paulo State. The aim of the work was to analyze biological aspects and distribution of Imparfinis minutus in the Ribeirao Grande microbasin (22[degree]4708[minute]''S, 45[degree]28[minute]17''W), in eastern Mantiqueira mountain range, from July 2001 to April 2002. Among the 37 species sampled, I. minutus (Siluriformes, Heptapteridae), was distributed from the piedmont to the plains of the Vale do Paraiba. The occurrence of this species was associated with the environments of small water volume, bottom with stones and gravel. The amplitude length of I. minutus was 4.75 to 12.75 cm. The length-weight relationship of the population was estimated at W = 0.0052 L3,13. Analyzing the alometric (Ka) and relative (Kr) condition factors, both indexes presented similar values. The lowest value was obtained in July, increasing gradually in October and January, and peaking in April. The analysis of the gonadossomatic relationship (GSR) of females showed higher values in July and January. The reproductive period of I. minutus occurred on spring/summer (October to January), as suggested by the gonadossomatic relationship and condition factor results. Feeding activity was constant, with fat visceral deposition concentrated in April and July. Imparfinis minutus is an aquatic insectivore opportunist species, consuming Diptera and Trichoptera larvae as secondary items. Most ingested food items were autochthonous resources.

Palaeomagnetism of the Mesozoic Serra Geral Formation, southern Brazil

Palaeomagnetic results from 20 volcanic sequences and 11 intrusive bodies (sills and dykes) of the Serra Geral Formation (Paraná Basin) are reported in this paper. The sequences are widespread all over the basin, while sills and dykes (Ponta Grossa arch) come from the northeastern portion. Three mean palaeomagnetic poles were computed for the Serra Geral Formation, which account for a time interval of ∼ 15 Ma. Pole SG1 is located at 85°S,108°E (α95 = 1.1°, N = 18) and represents the main phase of the magmatic activity in the basin, with a mean age of ∼ 135 Ma. Pole SG2 is located at 82°S,38°E (α95 = 7.8°, N = 2) and represents a younger magmatic phase, with an associated age of ∼ 130 Ma. Pole SG3 (72°S,37°E; α95 = 6.8°, N = 10) is the youngest pole. It is computed from the intrusive rocks and its age is assumed to be not younger than 118 Ma, the lower limit of the 'Cretaceous normal magnetic interval'. These three poles describe a shifting path, which suggest that the South American platform moved ∼ 5° southwards and rotated ∼ 10° clockwise during the Lower Cretaceous, preceding the South Atlantic opening. © 1990.

Caracterizacao litoquimica e aspectos petrologicos de rochas vulcanicas da Formacao Serra Geral: regiao centro-sul do Estado do Parana

This work defines the main volcanic types of Central-Southern Parana State (Serra Geral Formation), their stratigraphic relations, and which petrological process are able to explain the observed volcanic associations. -from English summary

Aspectos morfo-anatômicos de Paepalanthus hilairei koern. (Eriocaulaceae) da Serra do Cipó-MG

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Partilha de Recursos Alimentares em Peixes em um Riacho de Serra do Sudeste do Brasil

We studied the diet and food resources partitioning by fishes from the Itaúna stream, municipality of Itatinga, Southeastern Brazil. Eighteen species of fish were collected, being Microlepidogaster sp., Hypostomus sp., Astyanax sp., Phalloceros caudimaculatus and Heptapterus sp. the most frequent and abundant ones. Regarding diet, the majority of the species were observed to be insectivorous (61%), while insectivorous-herbivorous and periphyton feeders ranked 22 and 17%, respectively. The food overlap analysis revealed many cases of similarity between the diets. For most cases, however, a detailed analysis of food items and spatial distribution of the species showed differences between the couples under analysis which points toward a reduction in competition for food.