Espectroscopia Raman e difração de raio - x em cristais de LiNaSO4 e LiN3(SO4).6H2O

Abstract

In this work, we synthesized and grew single crystals of a lithium sodium sulfate hydrate morphology for the first time. Using single-crystal and powder X-ray scattering techniques, we described the chemical formula of these hydrated sulfates as LiNa3(SO4)26H2O (LNSH), their structure, unit cell parameters, crystallization sites of the ions and molecules of the chemical formula, and the number of molecules in the unit cell. We compared the structure determined for LNSH, which belongs to the space group, with the structure of LiNaSO4(LNS), which was determined by Morosim and Smith as C43V. We performed dielectric constant measurements on LNSH and LNS in the temperature range of 300K to 77K and conducted a rigorous study using polarized Raman scattering techniques as a function of scattering geometry and temperature in the range of 300K to 12K. These studies showed that both sulfates are stable in the temperature range mentioned above, which differentiates them from other sulfates of the type KLiSO4 (CKLS), LiNH4SO4 (CLAS) and LiCsSO4 (LCS), which experience phase transitions in the described temperature range. From our polarized Raman scattering studies, we performed a rigorous identification of the frequency values ​​of the Raman-active normal vibration modes at a temperature of 12k, in the irreducible A1 and E representations of the point group for LNSH and LNS. Based on our studies and comparing the results obtained from experiments performed on LNSH with other anhydrous sulfates such as LNS, KLS, LAS and LCS, we propose a classification of the Raman-active normal vibration modes according to their nature and type. In this classification, we were able to determine the frequency of internal modes of the type v1, V2, V4 of SO-24 ions and V1 and V3 of water molecules, Li-O type transitions, and also the modes of the four hydrogen bonds existing in the LNSH. We also performed a comparison of our results with those obtained by Teeters and Frech at the LNS, as well as a comparison between the results obtained using all the techniques described above for the LNSH and LNS. All parameters—the structure; the density, such as the values ​​of the dielectric constant as a function of temperature and the values ​​of the frequencies of the Raman-active normal vibration modes for the LNSH—represent a collection of data that are unprecedented in the literature, as well as results obtained at the LNS that complement the work of Teeters and Frech.