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Cubic Y zeolite were successfully synthesized using microwave heating for 18 - 25 min, whereas 10 - 50 h are required by hydrothermal heating technique depending upon the lattice Si/Al ratio. To this end, we used a commercial microwave oven modified in order to provide pulsed microwave pumping on the synthesis mixtures. The obtained samples were analyzed by X-ray diffraction, BET surface area and infrared spectroscopy measurements. As a result, we verify that Y zeolite samples obtained from hydrogels containing low aluminum contents, present a good degree of crystallinity and then can be suitable for using in adsorption and catalysis experiments.

Highlights: [•] High-pressure Raman spectra of β-BaTeMo2O9 were measured. [•] Pressure dependence of phonon modes was established. [•] Two structural phase transitions were discovered at 3.1 and 7.0GPa. [•] Mechanisms of these transitions were explained. [ABSTRACT FROM AUTHOR]

Abstract: In this work we report results of Raman scattering study on Cs4W11O35 and Rb4W11O35 in the 30–295K temperature range. Changes in the Raman spectra indicated presence of two structural phase transformations in the Cs4W11O35 (Rb4W11O35) system taking place at 110K (100K) and 165K (210K). These transformations lead to symmetry increase on cooling. Temperature dependence of Raman linewidths indicated larger contribution of an orientational mechanism in Cs4W11O35 than in the Rb4W11O35 system. No soft-like mode was observed that could point to a displacive type behavior at the phase transitions. Additional Raman scattering measurements were performed on the Cs4W11O35 system in the 300–820K range. No temperature-induced phase transitions were observed for this system above room temperature. [Copyright &y& Elsevier]

Abstract: This work reports high pressure Raman scattering results on dipotassium molybdate (K2MoO4). The effects of hydrostatic pressure on the vibrational properties of K2MoO4 has been investigated in the pressure range from 0.5 to 7.3GPa. This study also indicates that K2MoO4 crystals exhibit a pressure-induced first-order phase transition at about 2.2GPa from monoclinic to an unknown symmetry. Calculaions based on density-functional theory (DFT) unveiled the structural changes undergone by the K2MoO4 system under hydrostatic pressure. The phase transition is connected with the increase of the polyhedral KO6 distortion due to an increased anionic interaction as volume decrease, therefore leading to tiltings and/or rotations of the MoO4 tetrahedra. The consequence of such tiltings and/or rotations of the MoO4 tetrahedra is to increase the disorder of these units. The high-pressure phase transforms directly into the ambient-pressure phase as pressure is released. [Copyright &y& Elsevier]

Abstract: High pressure Raman scattering experiments were performed on RbFe(MoO4)2. These experiments revealed that two phase transitions take place in RbFe(MoO4)2 at very low pressures, i.e. between ambient pressure and 0.2GPa and between 0.4 and 0.7GPa. Raman results showed that at the first phase transition the room temperature P3̄m1 phase transforms into the P3̄ phase, which is also observed at ambient pressure below 190K. The second pressure-induced phase transition occurs into a low symmetry phase of unknown symmetry. The performed lattice dynamics calculations for the P3̄m1 phase and ab initio calculation of the structural changes under hydrostatic pressure helped us to get better insights into the mechanism of the observed phase transitions. [Copyright &y& Elsevier]

A high-pressure Raman scattering study of the tungstate Al2(WO4)3 is presented. This study showed the onset of two reversible phase transitions at 0.28±0.07 and 2.8±0.1 GPa. The pressure evolution of Raman bands provides strong evidences that both the transitions involve rotations/tilts of nearly rigid tungstate tetrahedra and that the structure of the stable phase in the 0.28–2.8 GPa range may be the same as the structure of the ambient pressure, low-temperature monoclinic (C2h5) ferroelastic phase of Al2(WO4)3. [Copyright &y& Elsevier]