Part III: lithium metasilicate (Li2SiO3)—mild condition hydrothermal synthesis, characterization and optical properties

Abstract

Li 2 SiO 3 nanopowders were synthesized via a non-stoichiometric 2:3 (S 1 ), 1:3 (S 2 ), 1:4 (S 3 ) and 1:5 (S 4 ) Li/Si molar ratios via hydrothermal reaction for 72 h at 180°C in an aqua solution using Li 2 CO 3 and H 2 SiO 3 as raw materials. The synthesized materials were characterized by powder X-ray diffraction (PXRD) technique and Fourier transform infrared spectroscopy. PXRD data showed that the crystal structure of the obtained materials is orthorhombic with the space group of Cmc2 1 . Also, to investigate the effect of the Li/Si molar ratio on the morphology of the obtained materials, the morphologies of the synthesized materials were studied by field emission scanning electron microscopy. The technique showed that with changing the Li/Si molar ratio from S 1 to S 4 , the morphology of as-prepared samples changed from flower structures to microrod-microsphere and then to a nonhomogenous layer-like structure. Ultraviolet-visible spectra showed that the nanostructure lithium silicate powders had good light absorption properties in the ultraviolet light region. It showed that with changing the Li/Si molar ratio from S 1 to S 4 , the calculated band gap was decreased. Also, cell parameter refinement showed that with changing the Li/Si molar ratio from S 1 to S 4 the cell parameters decreased. Photoluminescence analysis of the obtained materials was studied at the excitation wavelength of 247 nm. It showed that the emission spectra of the obtained materials had a blue shift from S 1 to S 4 .

Structural properties and mechanical stability of monoclinic lithium disilicate

“…The results for the valence and conduction bands confirm the existence of tetrahedral hybridisation of the SiO 4 framework. Similar findings were reported for orthorhombic Li 2 Si 2 O 5 .…”

“…Monoclinic Li 2 Si 2 O 5 has a large indirect band gap of 4.98 eV near the Fermi level (0 eV), which reveals that this material has an insulating nature in the C 1 c 1 phase. Similar electronic behaviour was reported for the Ccc 2 space group , with a band gap of close to 5 eV .…”

“…Lithium silicates are present as important phases in silicate glass ceramics and are of research interest due to their technological applications in lithium‐ion batteries , fast‐ion conductors , CO 2 adsorption , waveguides and solid breeding materials for tritium release in nuclear reactors . In particular, lithium disilicate (Li 2 Si 2 O 5 ) also has biomedical applications, exhibiting notable mechanical properties applicable in dentistry, as a high‐strength and machinable glass ceramic . It is also used as a substrate in storage media .…”

“…Lithium disilicate glass ceramics have three major phases: an orthorhombic (space group Ccc 2) stable form, an orthorhombic ( Pbcn ) metastable form and a monoclinic ( C 1 c 1) form . Many authors have noted that the monoclinic ( C 1 c 1) phase has very similar lattice parameters to the orthorhombic ( Ccc 2) form .…”

Part I: lithium metasilicate (Li2SiO3)—mild condition hydrothermal synthesis, characterization, and optical properties

“…1, with the Li:Si molar ratio of 2:3 in the reaction mixture, a highly pure crystalline phase of Li 2 SiO 3 (space group of Cmc2 1 [22][23][24][25][26][27] ) was obtained after 48, 72, and 96 h. So, it shows that with lithium nitrate and SiO 2 as raw materials the main phase is lithium metasilicate. Compared to our another works using lithium carbonate and silicic acid at 2:3 Li:Si molar ratio at 180°C for 72 h, the main phase was lithium metasilicate but the morphology of the obtained materials was flower structure [28]. Also, using lithium sulfate and silicic acid as raw materials at 2:3 Li:Si molar ratio at 180°C for 48 and 72 h, the main phase was lithium sodium silicate nanostructures with straw bundle-like structure [29].…”