P.F. Façanha Filho

Thermal and structural properties of Nd2O3-doped calcium boroaluminate glasses

Abstract Nd3+ doped CaO-Al2O-B2O3-CaF2 glasses were prepared by conventional melt-quenching technique, and their structural and thermal properties were studied. The amorphous nature of these samples was confirmed by X-ray diffraction (XRD). The measured density showed an increase with Nd2O3 doping, at the expense of CaO. Raman spectra presented changes with addition of Nd2O3, which indicated that the network structure of the glasses studied presented various borate groups, such as tetraborates, metaborates, ortho-borates and pyroborates units. The N4 values calculated from FTIR spectra revealed that incorporation of Nd2O3 into glass network converted the structural units from BO4 to BO3. From the analysis of DTA curves, we verified that Tg increased with the addition of Nd2O3; it was similar to the behavior caused by modifier oxides in the structure of borate glasses. Besides that, the calculated glass stability Tx–Tg for doped samples presented a decrease if compared to the undoped glass. Specific heat and thermal conductivity did not present significant changes with Nd2O3 concentration, up to 2.30 mol.%. The results of density, DTA, Raman and FTIR reinforced the idea that Nd2O3 acted as network modifier.

High pressure Raman spectra of monoglycine nitrate single crystal.

Single crystal of monoglycine nitrate has been studied by Raman spectroscopy under high pressures up to 5.5 GPa. The results show changes in lattice modes in the pressure ranges of 1.1-1.6 GPa and 4.0-4.6 GPa. The first change occurs with appearance of bands related to the lattice modes as well as discontinuity in the slope of dΩ/dP of these modes. Moreover, bands associated with the skeleton of glycine suggest that the molecule undergoes conformational modifications. The appearance of a strong band at 55 cm(-1) point to a second phase transition associated with the lattice modes, while the internal modes remain unchanged. These anomalies are probably due to rearrangement of hydrogen bonds. Additionally, decompression to ambient pressure shows that the phase transitions are reversible. Finally, the results show that the nitrate anions play an important role on the stability of the monoglycine nitrate crystal.