Journal of Raman Spectroscopy最新文献

The water quantification in nominally anhydrous minerals (NAMs) is always a scientific issue of great interest. Raman spectroscopic technique, which has been widely employed in planetary explorations (e.g., SHERLOC, SuperCam, and LRS), offers potential for in situ mineralogical and volatile analysis. However, the direct assessment of H₂O in silicates via Raman spectroscopy remains technically challenging, primarily due to the instability of water in silicate mixtures and the weak Raman signals of H₂O in such matrices. In this study, we propose an indirect approach by using K₂SO₄ as an intermediary to avoid the instability of water in silicate mixtures, thereby establishing a correlation between the content of silicate minerals (e.g., pyroxene) and water with the Raman peak intensity in silicate mixtures. The results indicate a strong linear relationship between the ratio of K₂SO₄ to pyroxene and the intensity ratio of the Raman peaks. Additionally, the Raman peak intensity of K₂SO₄ increases with the concentration of K₂SO₄ solutions. Based on the linear relationship, a model is proposed to evaluate the Raman peak intensity ratio between different ratios of water and silicate minerals. The Raman signal of water in homogeneous mixtures (silicate minerals and water) also weakens with decreasing water content. Therefore, we propose that Raman spectroscopy is a valuable technique for quantifying H₂O content in NAMs without the need to prepare unstable water-containing mixtures.

Lithium manganese oxide (LMO) is an effective absorbent for lithium recovery from brines, characterized by its high adsorption capacity, excellent regeneration performance, and selectivity. This study investigates the mechanisms of material degradation during lithium loading and unloading in LMO, employing a combination of time-resolved Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Key findings reveal that the A_1g vibrational mode wavenumber shifts from 635 cm⁻¹ at the onset of lithium ion exchange to 656 cm⁻¹ after 12 min, indicating local symmetry loss and manganese (Mn) loss during lithium intercalation. The proposed lithium exchange mechanism involves initial occupation of tetrahedral interstitial voids, followed by migration into interstitial sites between Mn octahedral sites. Computational modeling suggests that the loss of symmetry in MnO cubane-like groups occurs as lithium migrates, significantly affecting the Raman spectra. Importantly, the study demonstrates that after 100 cycles of lithium/hydrogen loading, a 24% loss in Mn is observed, which correlates with decreased structural stability; however, the structural integrity of LMO is enhanced when subjected to multiple cycles without complete loading. These insights contribute to the understanding of LMO's performance in lithium recovery applications and highlight potential strategies to optimize its use in future technologies.

Lapis lazuli is a semiprecious stone that falls under the category of blue-colored minerals that played a vital role in the cultural historic artwork throughout the world. Finding the provenance of lapis lazuli is a slightly challenging task. The sources of lapis lazuli pigments used at Ajanta Caves and its provenance have been a subject of interest and a research question. Six samples of lapis lazuli pigment of murals of 2nd century bce Ajanta Caves were examined using micro-Raman spectroscopy, Fourier transform infrared spectrophotometry (FTIR), X-ray fluorescence spectroscopy, spectrophotometry, X-ray diffractometry (XRD), and stereomicroscopy to find out the possible provenance raw materials through the mineralogical compositions. This study will be very helpful to tailor future conservation strategies. The results showed that these pigment samples are similar based on their composition, presenting diopside and specific trace element proportions as provenance markers. The results revealed that these raw materials for the lapis lazuli pigments used at Ajanta Caves may have been imported from lapis lazuli mines located at Badakhshan in Afghanistan, as the mines have been actively mined for over 6000 years, making them a significant source of lapis lazuli for ancient civilizations.

Graphite is a common mineral occurring in different metamorphic rocks, including high/ultrahigh-temperature and high/ultrahigh-pressure rocks. Raman spectroscopic studies combined with carbon isotope composition may highlight the carbon source (crustal or mantle) and PT conditions of graphite crystallization. In the present study, seven graphite-bearing samples of felsic granulite xenoliths from the “Eclogitovaya” pipe (the Eastern Pamir, Tajikistan) have been studied by Raman spectroscopy and analyzed its carbon isotope composition. Graphite crystals occur in the matrix as well as inclusions in rock-forming minerals (e.g., garnet and kyanite), indicating their simultaneous crystallization. The graphite formed as a result of the metamorphic transformation of carbonaceous material (δ¹³С ranges from −14.5‰ to −20.1‰) originally present in the rocks during subduction. Structural analysis of intact graphite inclusions in garnet revealed rims of disordered graphite surrounding well-ordered graphite cores. Composite inclusions consisting of disordered graphite, well-ordered graphite, and CO₂ were also observed. However, any evidence for precipitation of disordered graphite from fluid has not been found. It is likely that the origin of disordered graphite in the Eastern Pamir granulite xenoliths is attributed to the stress at the graphite–garnet interface during the rapid exhumation of the xenoliths.