Manganese oxides occur typically as cryptocrystalline and fine-grained mixtures of different Mn-phases, carbonates, silicates, and Fe oxides/hydroxides; thus their characterization by standard methods, such as X-ray diffraction, is extremely challenging. These materials have been widely used in various applications over the millennia, for example, in art works as pigments for pottery, mural paintings, stained glass, and recently, as nanostructured materials with very attractive physicochemical properties. Furthermore, they are important geomaterials that could play a key role in environmental applications, by controlling the partitioning of arsenic and heavy metals between rocks, soils, and aqueous systems. Raman spectroscopy, which is a punctual and nondestructive technique, has been widely used to characterize these materials. However, literature data are often conflicting and contradictory, usually not allowing a proper identification of the Mn species. In this work, we characterize the most common natural manganese oxides by combining X-ray powder diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy. Our data show that some manganese oxides have characteristic Raman spectra and can be easily recognized by using Raman spectroscopy alone, whereas integration of Raman data with other techniques is mandatory to characterize minerals that have almost identical Raman spectra. With this respect, Raman spectroscopy is the only technique allowing an easy discrimination between hollandite [Ba(Mn 4+ 6 ,Mn 3+ 2 )O 16 ] and cryptomelane [K(Mn 4+ 7 ,Mn 3+ )O 16 ]. The final goal of this work is to provide reference Raman spectra, acquired on previously well-characterized Mn samples to facilitate the application of Raman spectroscopy in the study of these geomaterials.

Manganese oxides are important geomaterials, widespread in terrestrial and Martian environments. Characterisation of the oxidation state of Mn is a central issue in science; this task has been addressed up to the present by X‐ray spectroscopy or diffraction techniques. The former, however, requires access to synchrotron facilities, while the latter does not provide crystal‐chemical information at the local scale. In this work, we compare a large set of Raman data from well‐characterised samples, already published by the same authors of this paper or as found in the literature. We show a clear correlation between the oxidation state of Mn and the wavenumber of peculiar bands; octahedrally co‐ordinated Mn2+ is recognised by a band around 530 cm−1, Mn3+ by a band around 580 cm−1 and Mn4+ by a band around 630 cm−1, while tetrahedrally co‐ordinated Mn2+ is recognisable by a band around 650 cm−1. Strongly distorted Mn3+ octahedra are indicated by the appearance of Jahn–Teller modes. Our method allows a reliable, easily accessible tool to characterise the oxidation states of Mn in oxides, also suitable for microscale mapping. It provides a robust analytical basis for the use of these minerals as redox indicators in geology/geochemistry, in exoplanetary research or for monitoring technological processes.

Raman spectra of groutellite and ramsdellite were provided and the thermal stability under the laser beam was investigated. Raman mapping allows the study of their distribution, which play a key-role in electrochemical activity of these compounds.

Gallium (Ga) doped silicon (Si) is becoming a relevant player in solar cell manufacturing thanks to its demonstrated low light-induced degradation, yet little is known about Ga-related recombination centers. In this paper, we study iron (Fe)-related recombination centers in as-grown, high quality, directionally solidified, monocrystalline Ga-doped Si. While no defect states could be detected by deep level transient spectroscopy, lifetime spectroscopy analysis shows that the minority carrier lifetime in as-grown wafers is dominated by low levels of FeGa related defect complexes. FeGa pairs have earlier been shown to occur in two different structural configurations. Herein, we show that in terms of recombination strength, the orthorhombic pair-configuration is dominant over the trigonal pair-configuration for FeGa. Furthermore, the defect energy level in the band gap for the orthorhombic defect center is determined to be EV + 0.09 eV, and the capture cross-section ratio of the same defect center is determined to be 220.

The current trend in silicon photovoltaics moving towards high‐quality thin mono‐crystalline silicon substrates sets a new challenge for the understanding of recombination mechanisms limiting the final performance of solar cells. Temperature‐ and injection‐dependent lifetime spectroscopy (TIDLS) has been shown to be a promising method for studying of high‐quality material with lifetime above 10 ms where the concentration of electrically active defects is well below the sensitivity of the most well‐known characterization techniques. In particular, when coupled with the Shockley–Read–Hall lifetime recombination model, TIDLS is capable of providing the most important defects' parameters including their energy level and concentration. In this contribution, we show that for a high‐quality silicon material, a thorough evaluation of the surface recombination velocity (SRV) temperature‐ and injection dependence is crucial for an accurate identification of the defects contained in the bulk. A new methodology for the analysis of TIDLS data, called defect parameters contour mapping, is introduced for the first time. By applying it to high‐quality n‐type float zone c‐Si samples passivated by a‐Si:H(i) or an a‐Si:H(i)/a‐Si:H(n) stack, we are able to assert the presence of defects in high lifetime materials in a range of concentration unachievable by any other characterization technique thus far. Copyright © 2016 John Wiley & Sons, Ltd.