Open Access

High-spectral resolution Raman spectroscopy is a powerful tool for the chemical and structural analysis in material sciences. Beyond its usage for the qualitative identification of minerals, Raman spectroscopy has been applied for the quantitative characterisation of chemical phases. The precise measurement of Raman peak position and band width values allows for an empirical differentiation of chemically similar phases and thus provides valuable insights to the structural properties of a material. In the field of archaeometry, the crystal structure of minerals can be used to elucidate the preparatory parameters of historical samples, such as the firing temperature. Comparison of historical materials with replicas produced under well-defined laboratory conditions help identify indicators for such process parameters. Previous Raman studies on pyrogenic anhydrite were able to distinguish between gypsum materials that were heated at different temperatures between 400–900 °C [1–3]. The results of thermal experiments with natural dolomite powder between 500–900 °C are presented, evaluating the thermal decomposition of dolomite and the consequent formation of calcium carbonate. Raman measurements were performed with excitation at 532 nm and 1800 mm-1 grating at room temperature on calcinated samples, as well as subsequently hydrated and re-carbonated samples. These high-resolution conditions are necessary to resolve the individual spectral contributions of different calcium/magnesium carbonate species. However, this sensitivity does not come without potential pitfalls. While the usage of micro-Raman spectroscopy with high spectral resolution shows great promise for evaluating minor shifts in peak positions and band widths, several technical aspects must be considered. For example, great care must be taken to exclude the thermal impact of the highly focused Raman laser on the sample. Similarly, exact standard operating procedures have to be followed to circumvent mechanical hysteresis in the alignment of the spectrographs’ grating. The influence of these two effects is presented and effective countermeasures are introduced to avoid resulting systematic errors. Statistical reliability and chemical imaging both rely on the individual analysis of thousands of Raman spectra. Thus, besides the spectral acquisition, also highly automated data analysis must be applied. Therefore, a peak-fitting routine using python scripts was employed to extract the peak positions and the full width at half maximum (FWHM) values of the ν1-, ν4- and L-bands of the carbonates. The results reveal the formation of Mg-calcite from dolomite at 700–750 °C and the formation of Mg-free calcite after calcination above 750 °C and subsequent hydration and re-carbonation (Fig. 1a). The findings from the thermal experiments are compared with Raman-microscopy mappings on medieval and reenacted mortars containing dolomite. Mg-calcite with comparable peak position and FWHM values have been successfully identified (Fig. 1b), proving Raman spectroscopy to be a suitable tool for elucidating the manufacturing procedures of anthropogenic materials.

The reconstruction of the thermal history of minerals is an on-going challenge in the study of anthropogenic materials, e.g., ceramics and mortar binders. For millennia carbonate rocks have been used as the starting material, though the exact manufacturing procedures are often unknown. Preparatory parameters such as firing temperature, heating and cooling rates, soaking time, and kiln atmosphere greatly influence the chemical and structural properties of the resulting products. Analysis of replicas produced under well-defined laboratory conditions help identify indicators for such process parameters and therefore provide valuable insights into historical production workflows. Raman micro-spectroscopy is a valuable method here because of its high sensitivity for crystal-chemical alterations coupled with a high spatial resolution. Previous studies on pyrogenic anhydrite were able to distinguish between gypsum materials that were heated at different temperatures between 400 – 900 °C [1, 2]. The results of thermal experiments with natural dolomite powder between 500 – 900 °C are presented, evaluating the thermal decomposition of dolomite and the consequent formation of calcium carbonate. Raman measurements were performed at room temperature on calcinated samples, as well as subsequently hydrated and re-carbonated samples. A peak-fitting routine using python scripts was employed to extract the peak positions and the full width at half maximum (FWHM) values of the ν1-, ν4- and L-bands of the carbonates. The results reveal the formation of Mg-calcite from dolomite at 700 – 750 °C and the formation of Mg-free calcite after calcination above 750 °C and subsequent hydration and re-carbonation. The findings from the thermal experiments are compared with Raman-microscopy mappings on medieval and reenacted mortars containing dolomite. Mg-calcite with comparable peak position and FWHM values have been successfully identified, proving Raman spectroscopy to be a suitable tool for elucidating the manufacturing procedures of anthropogenic materials.

The reconstruction of the thermal history of minerals is an on-going challenge in the study of anthropogenic materials, e.g., ceramics and mortar binders. For millennia carbonate rocks have been used as the starting material, though the exact manufacturing procedures are often unknown. Preparatory parameters such as firing temperature, heating and cooling rates, soaking time, and kiln atmosphere greatly influence the chemical and structural properties of the resulting products. Analysis of replicas produced under well-defined laboratory conditions help identify indicators for such process parameters and therefore provide valuable insights into historical production workflows. Raman micro-spectroscopy is a valuable method here because of its high sensitivity for crystal-chemical alterations coupled with a high spatial resolution. Previous studies on pyrogenic anhydrite were able to distinguish between gypsum materials that were heated at different temperatures between 400–900 °C [1-3]. The results of thermal experiments with natural dolomite powder between 500–900 °C are presented, evaluating the thermal decomposition of dolomite and the consequent formation of calcium carbonate. Raman measurements were performed at room temperature on calcinated samples, as well as subsequently hydrated and re-carbonated samples. Raman band positions and the full width at half maximum (FWHM) values of the ν1-, ν4- and L-bands of the carbonates are extracted and reveal the formation of Mg-calcite from dolomite at 700–750 °C and the formation of Mg-free calcite after calcination above 750 °C and subsequent hydration and re-carbonation. The findings from the thermal experiments are compared with Raman-microscopy mappings on medieval and reenacted mortars containing dolomite. Mg-calcite with comparable peak position and FWHM values have been successfully identified, proving Raman spectroscopy to be a suitable tool for elucidating the manufacturing procedures of anthropogenic materials.

Synthesis of pure, homogeneous, and reproducible materials is key for the comprehensive understanding, design, and tailoring of material properties. In this study, we focus on the synthesis of ZrV2O7, a material known for its negative thermal expansion properties. We investigate the influence of solid-state and wet chemistry synthesis methods on the purity and homogeneity of ZrV2O7 samples. Our findings indicate that different synthesis methods significantly impact the material's characteristics. The solid-state reaction provided high-purity material through extended milling time and repeated calcination cycles, while the sol-gel reaction enabled a “near-atomic” level of mixing and, therefore, homogenous phase-pure ZrV2O7. We confirmed purity via X-ray diffraction and Raman spectroscopy, highlighting differences between phase-pure and multiphase ceramics. These analytical techniques allowed us to distinguish subtle differences in the structure of the material. Based on ab initio simulated phonon data, we were able to interpret the Raman spectra and visualise Raman active atom vibrations. We show that phase purity enables the unbiased characterisation of material properties such as negative thermal expansion.