Publications by authors named "Frederico G Alabarse"
Article Synopsis
- * The structure of CsPb(Br,I) changes from a two-dimensional tetragonal framework at lower temperatures to a three-dimensional cubic structure at higher temperatures, especially above 630 K, where significant deficiencies in Cs and (Br,I) occur.
- * Studies reveal a very low thermal conductivity linked to the material’s properties, alongside optical gap measurements that align with theoretical calculations, indicating promise for use in energy applications.
Article Synopsis
- Pressure can transform the single crystal form of the porous aluminophosphate AlPO-17 into an amorphous state starting at 0.6 GPa, without breaking into smaller crystals.
- The amorphous material maintains the shape and orientation of the original crystal while compressing around the empty pores, indicating a direct structural relation between the two forms.
- This process could lead to the creation of high-quality amorphous materials, known as "perfect glasses," with enhanced mechanical properties due to a notable memory effect upon decompression.
The porous aluminophosphate AlPO-17 with a hexagonal erionite structure, exhibiting very strong negative thermal expansion, anomalous compressibility, and pressure-induced amorphization, was studied at high pressure by single-crystal and powder X-ray diffraction in the penetrating pressure transmitting media N, O, and Ar. Under pressure, these guest species were confirmed to enter the pores of AlPO-17, thus completely modifying its behavior. Pressure-induced collapse in the plane of AlPO-17 no longer occurred, and this plane exhibited close to zero area compressibility.
View Article and Find Full Text PDFThe dynamical properties of water molecules confined in the unidirectional hydrophilic nanopores of AlPO-54 are investigated with quasi-elastic neutron scattering as a function of temperature down to 118 K. AlPO-54 has among the largest pores known for aluminophosphates and zeolites (about 1.3 nm), though they are small enough to prevent water crystallization due to the high degree of confinement.
View Article and Find Full Text PDFWe have studied by means of angle-dispersive powder synchrotron X-ray diffraction the structural behavior of KCaPO, SrKPO, and KCe(PO) under high pressure up to 26, 25, and 22 GPa, respectively. For KCaPO, we have also accurately determined the crystal structure under ambient conditions, which differs from the structure previously reported. Arguments supporting our structural determination will be discussed.
View Article and Find Full Text PDFSrAlSi crystallizes into either a semimetallic, CaAlSi-type, α phase or a superconducting, BaZnP-type, β phase. We explore possible transformations by employing pressure- and temperature-dependent free-energy calculations, vibrational spectral calculations, and room-temperature synchrotron powder X-ray diffraction (PXRD) measurements up to 14 GPa using a diamond anvil cell. Our theoretical and empirical analyses together with all reported baric and thermal events on both phases allow us to construct a preliminary - diagram of transformations.
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- Researchers successfully synthesized polymer-guest/zeolite-host nanocomposites using liquid phenylacetylene in VFI at high pressure, providing a more practical approach than previous methods.
- The resulting composite features disordered polyphenylacetylene chains within the zeolite's pores, characterized through advanced techniques like synchrotron X-ray diffraction and nuclear magnetic resonance spectroscopy.
- The newly developed materials exhibited promising gas sensing capabilities, particularly for detecting water and butanol vapors, demonstrating their potential for future technological applications.
The incorporation of guest species in zeolites has been found to strongly modify their mechanical behavior and their stability with respect to amorphization at high pressure (HP). Here we report the strong effect of HO on the pressure-induced amorphization (PIA) in hydrated AlPO-17. The material was investigated in-situ at HP by synchrotron X-ray powder diffraction in diamond anvil cells by using non- and penetrating pressure transmitting media (PTM), respectively, silicone oil and HO.
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- The study examined how water (H2O) is inserted into a material called AlPO4-54·xH2O using techniques like X-ray diffraction and molecular simulations.
- It was found that water molecules tend to cluster near the walls of the material's pores and that their arrangement is quite disordered.
- While adding water helps to prevent the material from collapsing, it also leads to the beginning of chemical bonds forming between water and aluminum, which can cause the material to amorphize (lose its crystalline structure).
Proficiency tests in the determination of activity of radionuclides in radiopharmaceutical products measured by nuclear medicine services in 8 years of comparison programmes in Brazil.
Appl Radiat Isot
August 2008
Proficiency tests were applied to assess the performance of 74 nuclear medicine services in activity measurements of (131)I, (123)I, (99)Tc(m), (67)Ga and (201)Tl. These tests produced 913 data sets from comparison programmes promoted by the National Laboratory for Ionizing Radiation Metrology (LNMRI) from 1999 to 2006. The data were evaluated against acceptance criteria for accuracy and precision and assigned as Acceptable or Not acceptable accordingly.
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- Brazil's Nuclear Medicine Services (NMS) use dose calibrators to measure radiopharmaceutical activity for patient diagnosis and treatment, emphasizing the need for accuracy in these measurements.
- Since 1998, the National Laboratory for Ionizing Radiation Metrology (LNMRI) has successfully run a quality control program for measuring radiopharmaceutical activity in Rio de Janeiro but aims to expand nationwide.
- A network of regional laboratories in Brasília and Porto Alegre has been established, demonstrating the feasibility of conducting radionuclide metrology comparisons for isotopes like 131I and 99Tcm across the country.