Micro-Raman spectroscopy offers improved capability to identify and characterize natural Mn oxide phases thereby providing better understanding of the role of Mn oxide minerals in the environment and permitting more accurate comparisons of laboratory experiments to natural systems.  A primary advantage of the Raman technique is that the spectra provide information about local atomic coordination environments as well as longer-range structure, and therefore, it can be a useful probe even for highly disordered materials.   Modern instruments typically offer multiple laser options and high-sensitivity detectors that provide a range of data collection conditions that can be optimized for particular samples.  These micro-Raman systems have the potential to provide phase identification and structural information quickly and easily from discrete areas (~ 1 µm spot size) on natural or synthetic Mn oxide samples.  Moreover, high-spatial resolution Raman mapping is a standard capability in most new instruments. We present here results of a comprehensive Raman study from a large assortment of well-characterized natural and synthetic Mn oxide samples, using a variety of data collection conditions.  We demonstrated that when using multiple lasers, especially at 785 and 532 or 633 nm wavelengths, and low incident powers (30 – 500 µW, depending upon the laser light and sample), we can unambiguously identify Mn oxide phases for most samples.  Finally, we explore spectral trends for some specific phases that provide insights about composition, crystal structure, symmetry, and Mn oxidation states. With our comprehensive Raman database of well-characterized Mn oxide standards and use of appropriate data collection conditions, micro-Raman is a powerful tool for identification and characterization of biotic and abiotic Mn oxide phases from diverse natural settings (including on other planets), and thereby can provide new insights into the roles of these phases in our environment.

Raman spectroscopy identification and characterization of natural and synthetic manganese oxides

ACS Spring Meeting 2021

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