Structural State Preceding the First-Order Phase Transition of Li2SO4

Acoustic Shock Wave-Induced Amorphous to Crystalline Phase Transitions of Li2SO4─Raman Spectroscopic and Thermal Calorimetric Approach

“…Note that as per the literature reports on the thermal properties of the title sample, there is no report found for the amorphous state (both the translational and librational disorder-induced amorphous states). β-Li 2 SO 4 is transformed into the α-Li 2 SO 4 at 575 °C, which can be slightly changed based on the heating rates. − So, in this aspect, it is not possible to find direct evidence for the translational and librational disorder-induced amorphous states, but the clear indication of the formation of β-Li 2 SO 4 based on the transition temperature points of the β–α-Li 2 SO 4 can be authenticated. ,,− The zoomed-in transition temperature regions of β–α-Li 2 SO 4 with respect to the number of shock pulses are presented in Figure b, wherein a few changes could be seen in the respective transition temperature points such that the observed values are 581, 582.7, 585, and 580 °C for the 0, 1, 2, and 3 shocked conditions, respectively. The observed values of the transition temperature point are quite high compared to the reported values, and such a kind of shift in the transition temperature points that the higher temperature is quite common. − The crystalline counterparts have higher transition points than the amorphous counterparts, and similar results are also found in the crystalline to the amorphous transitions of NiSO 4 ·6H 2 O under shocked conditions. , Note that among the four transition temperature points, the second shocked condition’s point is quite high compared to the other shocked samples’ transition temperature points (Figure ), whereby a clear indication for the formation of β-Li 2 SO 4 is ensured. ,− Note that in the case of β-Li 2 SO 4, the coupling of Li–SO 4 is quite stable because of the high compressibility; it requires quite a higher thermal energy to induce phase transition in β–α-Li 2 SO 4 compared to the other samples. ,− As seen in Figure , both the amorphous states of the control and the third shocked sample have almost similar transition points, whereas at the first shocked condition, the transition point is slightly increased, which is due to the formation of the glassy state, which is well corroborated with the previously reported XRD results …”

“…The recorded Raman spectra of the control and shocked Li 2 SO 4 samples are shown in Figure 1. First and foremost, it is highly essential to have clear-cut information about the β- For example, the most intense SO 4 symmetric Raman line υ 1 (A g -B g ) is exhibited at 1014 cm −1 (with an argon−krypton laser tuned to 514 nm) 23,24 and at 1007 cm −1 (532 nm laser source), 29,31 while the doublet structure originating from sulfate ion's internal modes of υ 2 and υ 4 Raman bands are located at 447 (A g ), 513 (B g ), 617 (B g ), and 665 cm −1 (A g -B g ). 23,24 The first two lower Raman band locations belong to υ 2 , and the next two Raman band locations belong to υ 4 .…”

“…First and foremost, it is highly essential to have clear-cut information about the β-Li 2 SO 4 Raman spectral line features of various Raman regions. For example, the most intense SO 4 symmetric Raman line υ 1 (A g -B g ) is exhibited at 1014 cm –1 (with an argon–krypton laser tuned to 514 nm) , and at 1007 cm –1 (532 nm laser source), , while the doublet structure originating from sulfate ion’s internal modes of υ 2 and υ 4 Raman bands are located at 447 (A g ), 513 (B g ), 617 (B g ), and 665 cm –1 (A g -B g ). , The first two lower Raman band locations belong to υ 2 , and the next two Raman band locations belong to υ 4 . The υ 3 Raman band regions exhibit multiplet Raman bands, and their locations are 1116 (A g ), 1123 (B g ), 1127 (B g ), 1147 (A g ), 1194 (B g ), and 1204 cm –1 (A g ), respectively. ,, According to previous reports, the monoclinic structure of Li 2 SO 4 (β-Li 2 SO 4 ) has the lattice Raman bands at 446 (A g ), 427 (B g ), 419 (A g ), 385 (B g ), 362 (A g ), 343 (A g ), and 305 (B g ) cm –1 , which belong to Li ions’ lattice modes, while the positions 212 (A g ), 176 (B g ), 162 (A g ), 134 (A g ), 119 (A g ), 108 (A g ), 94 (A g ), 89 (A g ), 81 (B g ), and 73 (B g ) cm –1 arise out of the SO 4 lattice Raman bands …”

“…The crystalline structures of α and β-Li 2 SO 4 crystals advocated through the Raman spectroscopic data have been reported by several authors, − and α-Li 2 SO 4 is a high-temperature phase. The Raman spectral features of room temperature phase β-Li 2 SO 4 have also been reported in various experimental aspects such as chemical incorporation, strong electric fields, and high temperature. , According to ref during the nitrogen chemical incorporation conditions, nitrogen replaces oxygen in the SO 4 tetrahedra and the nitrogen–nitrogen bridge is formed between the two anions, which significantly affects the features of the Raman bands. At high-voltage pulsed electric discharge conditions, Li 2 SO 4 experiences an enhancement in the translational mobility of Li ions such that the reduction of the Li–SO 4 bond strength is enabled .…”

“…At high-voltage pulsed electric discharge conditions, Li 2 SO 4 experiences an enhancement in the translational mobility of Li ions such that the reduction of the Li–SO 4 bond strength is enabled . At high-temperature conditions (873 K), the υ 1 Raman band (∼1014 cm –1 ) is shifted to 960 cm –1 , wherein it belongs to the cubic structure of Li 2 SO 4 (α-Li 2 SO 4 ). , Note that in the case of α-Li 2 SO 4, the vibrational multiplet structure originating from sulfate ion internal modes (υ 2 , υ 4 , and υ 3 ) is converted into the singlet Raman band and generally experiences the lower Raman shift. Most importantly, the lithium Raman modes’ intensities are linearly reduced, while increasing the temperature up to 350 °C, whereas while further increasing the temperature, they completely disappear .…”