Raman scattering of rare earth sesquioxide Ho2O3: A pressure and temperature dependent study

Pressure and temperature dependent Raman scattering studies on Ho2O3 have been carried out to investigate the structural transition and the anharmonic behavior of the phonons. Ho2O3 undergoes a transition from cubic to monoclinic phase above 15.5 GPa, which is partially reversible on decompression. The anharmonic behavior of the phonon modes of Ho2O3 from 80K to 440K has been investigated. We find an anomalous line-width change with temperature. The mode Gruneisen parameter of bulk Ho2O3 was estimated from high pressure Raman investigation up to 29 GPa. Furthermore, the anharmonic components were calculated from the temperature dependent Raman scattering

Investigations of anharmonic effects via phonon mode variations in nanocrystalline Dy2O3, Gd2O3 and Y2O3

The nanocrystalline rare earth sesquioxides Dy2O3, Gd2O3 and Y2O3 have been investigated for anharmonic effects in the temperature range 80-440K using Raman spectroscopy. These samples were cubic in structure under ambient conditions with particle sizes in nano-range. The predominant T-g+A(g) phonon modes of the samples primarily exhibited phonon softening in the investigated temperature range. However, the line width variations clearly reflected the variations in the effects of anharmonicity on these samples, and the related anharmonic constants were estimated. The mode Grueneisen parameters required for these studies were deduced from our own high-pressure data for these samples reported earlier. The line width variations for these samples were found to display similar trends; however, their magnitudes were indicative of the factors that are expected to contribute to the variation in phonon behaviour

Temperature Dependent Variations of Phonon Interactions in Nanocrystalline Cerium Oxide

The temperature dependent anharmonic behavior of the phonon modes of nanocrystalline CeO2 was investigated in the temperature range of 80–440 K. The anharmonic constants have been derived from the shift in phonon modes fitted to account for the anharmonic contributions as well as the thermal expansion contribution using the high pressure parameters derived from our own high pressure experimental data reported previously. The total anharmonicity has also been estimated from the true anharmonicity as well as quasiharmonic component. In the line-width variation analysis, the cubic anharmonic term was found to dominate the quartic term. Finally, the phonon lifetime also reflected the trend so observed

Anharmonic behavior and structural phase transition in Yb2O3

The investigation of structural phase transition and anharmonic behavior of Yb2O3 has been carried out by high-pressure and temperature dependent Raman scattering studies respectively. In situ Raman studies under high pressure were carried out in a diamond anvil cell at room temperature which indicate a structural transition from cubic to hexagonal phase at and above 20.6 GPa. In the decompression cycle, Yb2O3 retained its high pressure phase. We have observed a Stark line in the Raman spectra at 337.5 cm−1 which arises from the electronic transition between 2F5/2 and 2F7/2 multiplates of Yb3+ (4f13) levels. These were followed by temperature dependent Raman studies in the range of 80–440 K, which show an unusual mode hardening with increasing temperature. The hardening of the most dominant mode (Tg + Ag) was analyzed in light of the theory of anharmonic phonon-phonon interaction and thermal expansion of the lattice. Using the mode Grüneisen parameter obtained from high pressure Raman measurements; we have calculated total anharmonicity of the Tg + Ag mode from the temperature dependent Raman data

Properties of carbon particles in archeological and natural Amazon rainforest soils

Driving practices of Amazon native inhabitants are an example of positive feedback in carbon storage acting as a key element in soil fertility and stability. The anthropogenic Amazonian Terra Preta do Índio (Indian Dark Earth) soils are rich in pyrogenic black carbon and the Rio Negro (Black River) also exhibits plentiful apparently similar black-carbon particles. In this context, we characterized the structural, morphological and elemental properties of the long-lived stable carbon-based structures present in sediments of the Amazonian Rio Negro and in two Terra Preta do Índio soils from two different geographic regions. Optical microscopy, Raman spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques are utilized. The structural analysis displayed that these carbon structures exhibit similar nanocrystallite structures, despite their different geographic location and environment. The Terra Preta do Índio-carbons are however, more defective and the quantitative elemental analyzes indicate they have greater variety of nutrients, such as P and Ca, than Rio Negro sediment-carbons. © 2020 Elsevier B.V