Search results for "MINERALOGY"
showing 10 items of 1516 documents
Mechanism of crystallization of Co-cordierites from stoichiometric powdered glasses
2002
Abstract The influence of cobalt, as a divalent cation, on the crystallization behaviour of the cordierite based glasses was studied. Powdered glass specimens of stoichiometric composition 2MO 2Al 2 O 3 5SiO 2 (M=Co and/or Mg) were obtained and thermally treated at several temperatures and times, and the sequence of crystallization and their microstructural evolution were analysed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Results on the crystallization sequence showed that the steps in the crystallization path are independent of the nature of the divalent cation. The first crystalline phase detected displayed the μ-cordierite structure, i.e. a solid…
Disorder-induced Raman scattering in rhenium trioxide (ReO3)
2007
Raman scattering in cubic metallic perovskite (ReO3) was studied at room temperature for well-crystallized monolith, polycrystalline powder and thin film samples. Defect-induced first-order Raman scattering was detected from the sub-surface region, given by the penetration depth of a 633 nm laser, and its origin was explained on the basis of a rigid-ion vibrational model for bulk ReO3. A quenching of the Raman intensity was observed in crystalline monolithic ReO3 upon increasing the temperature up to 250 °C and was related to crystal surface reconstruction/annealing.
Processing and properties of nanocrystalline Pb(Sc0.5Ta0.5)O3, Pb(Sc0.5nb0.5)O3 and Pb(Mg1/3Nb2/3)O3 films produced by RF-sputtering from ceramic tar…
2000
Abstract Nanocrystalline thin films of different relaxor materials, namely Pb(Sc0.5Ta0.5)O3 (PST), Pb(Sc0.5Nb0.5)O3(PSN), Pb(Mg1/3Nb2/3)O3(PMN) have been produced by RF-sputtering to investigate whether it will affect their dielectric properties if their grain size is reduced to the dimensions known from their nanodomains. The XRD shows that the amorphous film crystallizes in pyrochlore structure at lower temperatures and short times. Annealing at higher temperatures and far longer time intervals leads to an increasing amount of perovskite phase with a grain size in the nanometer range. These results including dielectric measurements will be presented and discussed.
Study of the defects in La3Ta0.5Ga5.5O14 single crystals
2016
Abstract Defects that are formed during crystal growth pose a serious obstacle for potential application of La 3 Ga 5.5 Ta 0.5 O 14 (LGT) as a laser or piezoelectric crystal. We have performed the study of the defects origin in LGT crystals grown in different atmospheres using optical, EPR and time-resolved luminescence characterization methods. The absorption bands detected in the transparency region at 290, 360 and 490 nm ( T =300 K) demonstrate different dependence on crystal annealing in vacuum and air. EPR analysis demonstrated that the defects responsible for these bands are non-paramagnetic. X-ray irradiation results in hole trapping by oxygen ions thus forming O − centers perturbed …
Atomic layer deposition and characterization of biocompatible hydroxyapatite thin films
2009
Abstract Atomic layer deposition (ALD) was used to produce hydroxyapatite from Ca(thd) 2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) and (CH 3 O) 3 PO onto Si(100) and Corning (0211). Film crystallinity, stoichiometry, possible impurities and surface morphology were determined. The as-deposited films contained significant amounts of carbonate impurities however, annealing at moist N 2 flow reduced the carbonate content even at 400 °C. The as-deposited Ca–P–O films were amorphous but rapid thermal annealing promoted the formation of the hydroxyapatite phase. Mouse MC 3T3-E1 cells were used for the cell culture experiments. According to the bioactivity studies cell proliferation was enhanc…
Luminescence of Er/Yb and Tm/Yb doped FAp nanoparticles and ceramics
2015
The nanoparticles of hydroxiapatite and fluorapatite doped with Er/Yb and Tm/Yb were synthesized and characterized by FTIR, XRD, SEM and TEM methods. The results of up-conversion luminescence studies were presented for the samples as prepared, annealed at 500°C and at 900-1000 °C. At annealing above 800°C the ceramic state was formed. It is shown that fluorapatite host is more appropriate than hydroxiapatite host for rare ions luminescence and up-conversion processes. The post preparing annealing of nanarticles significantly enhanced the luminescence intensity. The Tm/Yb doped fluorapatite shows intense up-conversion luminescence in 790-800 nm spectral region and is potentially useful for b…
Low-temperature atomic layer deposition of ZnO thin films: Control of crystallinity and orientation
2011
Abstract Low-temperature atomic layer deposition (ALD) processes are intensely looked for to extend the usability of the technique to applications where sensitive substrates such as polymers or biological materials need to be coated by high-quality thin films. A preferred film orientation, on the other hand, is often required to enhance the desired film properties. Here we demonstrate that smooth, crystalline ZnO thin films can be deposited from diethylzinc and water by ALD even at room temperature. The depositions were carried out on Si(100) substrates in the temperature range from 23 to 140 °C. Highly c-axis-oriented films were realized at temperatures below ~ 80 °C. The film crystallinit…
Traversing Phase Fields towards Nanosized Beta Tricalcium Phosphate
2013
The difficulty of beta tricalcium phosphate (β-TCP) crystallization in aqueous media opens the question whether β-TCP can be produced using an alternative pathway. Amorphous calcium phosphate (ACP) is metastable in an aqueous environment and prefers a more stable apatite phase. Others have transformed a crystallized calcium deficient hydroxyapatite (Ca-def HAp) into β-TCP, but automatic transformation from ACP to Ca-def HAp followed by transformation to β-TCP has not been addressed. This work shows the formation of Ca-def HAp after different aging times of ACP and the subsequent transition to β-TCP. An amorphous phase with a Ca/P ratio of 1.5 was synthesized, rinsed, filtered and excess flu…
Double pulse laser induced breakdown spectroscopy applied to natural and artificial materials from cultural heritages
2009
Abstract The laser-induced breakdown spectroscopy (LIBS) is an applied physical technique that has shown in recent years its great potential for rapid qualitative analysis of materials. Thanks to the possibility to implement a portable instrument that perform LIBS analysis, this technique is revealed to be particularly useful for in situ analysis in the field of cultural heritages. The purpose of this work is to evaluate the potentiality of LIBS technique in the field of cultural heritages, with respect to the chemical characterization of complex matrix as calcareous and refractory materials for further quantitative analyses on cultural heritages. X-Ray Fluorescence (XRF) analyses were used…
Ordering of fluorite-type phases in erbium-doped oxyfluoride glass ceramics
2018
In this study, novel transparent Er3+ doped glass ceramics were prepared from melt-quenched oxyfluoride glasses with general composition of Na2O-NaF-BaF2-YbF3-Al2O3-SiO2. The crystallization of fluorite (BaF2, BaF2-YbF3, NaF-BaF2-YbF3 and Na0.5-xYb0.5+xF2+2x) and distorted fluorite (rhombohedral Ba4Yb3F17 and tetragonal NaF-BaF2-YbF3) phases was analysed in glass ceramics with different BaF2 and YbF3 ratio. The phase composition and microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Intense red upconversion luminescence (UCL) was detected under near-infrared excitation resulting from three photon upconversion followed by cross-relaxation betw…