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Abstract:In this work, a set of nanoparticles of Nb 2 O 5 nanoparticles were grown by both the Pechini and the sol-gel methods. The amorphous materials were calcined at 650 • C or at 750 • C. X-ray diffraction, scanning electron microscopy, luminescence and Raman spectroscopy were used in order to characterize the materials. From the study, it is possible to state that the method of production of nanoparticles, beyond the temperature of synthesis, has a great influence on whether the phase produced is hexagonal or orthorhombic. Additionally, compared to de Sol-gel method, the Pechini method produced samples with smaller particle sizes. The photoluminescence spectra of niobium pentoxide nanostructure materials show that the emission peaks are positioned between 334 to 809 nm and there is a change of intensity which varies depending on the synthesis route used. High pressure Raman spectra at room temperature were obtained from two samples grown by the sol-gel method. Up to 6 GPa, where it is possible to observe the Raman bands, no modification other than the increase of disorder was observed, and this can be associated with a change of phase.

We report for the first time phonon properties of [CH3CH2NH3][Mg(HCOO)3] (EtAMg). The studied compound undergoes two structural temperature‐induced phase transitions and temperature‐dependent Raman and infrared studies let us to obtain insight into mechanism of these transitions. In particular, very large broadening of infrared and Raman bands, attributed to vibrations of the NH3 groups, revealed highly dynamic nature of these groups in the both high‐temperature phases. This result indicates that the phase transitions at 374 and 426 K are associated with disordering of the template cations. Raman and infrared data also show that both phase transitions are accompanied by significant distortion of the anionic framework. We also present the pressure‐dependent Raman data of EtAMn framework up to 7.1 GPa. These data revealed presence of two pressure‐induced phase transitions, one between 3.7 and 4.0 GPa and second between 5.6 and 6.0 GPa. We discuss mechanisms of these transitions. Copyright © 2017 John Wiley & Sons, Ltd.

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