Natural yellow earth pigments are heterogeneous mineral assemblages dominated by iron (hydr)oxides and accompanied by variable accessory phases such as quartz, calcite, gypsum, and aluminosilicates. Although these accessory minerals may encode geological origin, their reliable identification from bulk Raman spectra is complicated by multiphase band overlap, fluorescence background, and particle-level heterogeneity. As a result, mineral discrimination from Raman data alone remains analytically demanding. Here, we examine whether systematic post-acquisition processing can enable robust mineral-based differentiation of closely related pigments using Raman spectroscopy alone. Five yellow earth pigments (three yellow ochres and two raw siennas) were analyzed using particle-resolved confocal Raman spectroscopy, generating statistically representative datasets (>200 spectra per sample). Mineral identification was performed using three strategies, visual interpretation, automated three-component spectral library fitting (3C model), and supervised machine learning classification (XGBoost), and assessed using a binary presence/absence scheme to support comparison across heterogeneous particle populations. Both the 3C and XGBoost approaches enabled statistical separation of all five pigments, whereas K-means cluster analysis of the visual interpretation did not distinguish between the two raw siennas. Together, these results support a reproducible Raman-only workflow for preliminary mineral assignment and pigment discrimination in provenance-oriented cultural heritage studies.

Phase relations in Cr 3 S 4 and the substituted system Cr 3 S 4– x Se x are studied to determine the influence of chemical substitutions on the thermoelectric properties. In addition to the expected equilibrium phase crystallizing in the monoclinic space group I 2/ m , some samples exhibit a defect phase with Cr 2 S 3 -like structure. The defect phase can be observed in a few samples prior to sintering, with the majority being phase-pure Cr 3 S 4 . The defect phase can, however, be introduced in phase-pure samples through in situ heating. It can be proven that the defect phase has an influence on the thermoelectric properties, by lowering the electrical and thermal conductivity, while increasing the Seebeck coefficient. Substitution in the anion lattice of Cr 3 S 4 with Se lowers the thermal conductivity. The improvement is mainly achieved through a reduction of the electronic contribution to the thermal conductivity, leading to total values as low as 1.6 Wm −1  K −1 for the substituted system in comparison to the pristine material 2.3 Wm −1  K −1 .

Phase relations in Cr3S4 and the substituted system Cr3S4–x Se x are studied to determine the influence of chemical substitutions on the thermoelectric properties. In addition to the expected equilibrium phase crystallizing in the monoclinic space group I2/m, some samples exhibit a defect phase with Cr2S3‐like structure. The defect phase can be observed in a few samples prior to sintering, with the majority being phase‐pure Cr3S4. The defect phase can, however, be introduced in phase‐pure samples through in situ heating. It can be proven that the defect phase has an influence on the thermoelectric properties, by lowering the electrical and thermal conductivity, while increasing the Seebeck coefficient. Substitution in the anion lattice of Cr3S4 with Se lowers the thermal conductivity. The improvement is mainly achieved through a reduction of the electronic contribution to the thermal conductivity, leading to total values as low as 1.6 Wm−1 K−1 for the substituted system in comparison to the pristine material 2.3 Wm−1 K−1.

The effects of low-level partial cation substitution in Cr2−xMxS3 with M = Ti, V or Sn and x = 0.05 and 0.1 have been investigated regarding the long- and short-range crystal structures and thermoelectric properties. All substituted compounds crystallized in the equilibrium phase of Cr2S3, adopting the space group R $${\overline{\text{3}}}$$ . Electron beam irradiation led to a phase transformation from space group R $${\overline{\text{3}}}$$ to P $${\overline{\text{3}}}$$ 1c with a subsequent appearance of diffuse scattering, indicating short-range ordering of cations in the partially occupied cation layers. Substitution of Cr by V led to a reduction in electrical conductivity and subsequently to a lower thermoelectric performance in comparison to the pristine material. In contrast, substitution with Ti yielded an improvement of the performance due to a higher electrical conductivity and a reasonably high Seebeck coefficient. Both Sn-substituted compounds contained only traces of Sn. Surprisingly, a significant improvement of the electrical conductivities could be observed in comparison to the pristine material as well as the other Cr2−xMxS3 materials.

Here, we report on the time dependence of a synthesis procedure for generation of both n- and p-type bismuth telluride-based materials. To initiate the reaction, the starting materials were first mechanical pre-reacted. The Rietveld refinements of X-ray diffraction (XRD) data collected after different milling times demonstrate that Bi2Te3 was formed after only 10 min, and longer milling times do not alter the composition. To complete the phase formation, the powders were treated by field-assisted sintering and heat treatment afterwards. The effect of this fast procedure on the structural and thermoelectric properties was investigated. Samples were obtained with relative densities above 99%. A clear preferred orientation of the crystallites in the samples is evidenced by Rietveld refinements of XRD data. The thermoelectric characteristics demonstrate a good performance despite the short milling time. Further, it was demonstrated for this fast synthesis that the physical transport properties can be varied with well-known n- and p-type dopants like CHI3 or Pb. For these non-optimized materials, a ZT value of 0.7 (n-type) and 0.9 (p-type) between 400 and 450 K was achieved. The long-term stability is demonstrated by repeated measurements up to 523 K showing no significant alteration of the thermoelectric performance.

The influence of low‐level metal cation substitution in the thermoelectric material NiCr2S4, treated via field‐assisted sintering, is investigated in X‐ray diffraction (XRD) and transmission electron microscopy (TEM) studies. NiCr2S4 and Mn0.1Ni0.9Cr2S4 can be synthesized and compacted as phase‐pure pellets, while In0.1Ni0.9Cr2S4 appears as a mixture of different phases. XRD investigations reveal that Mn can be incorporated into the host material's Ni lattice sites, while In is mainly incorporated into additional phases. Both NiCr2S4 and Mn0.1Ni0.9Cr2S4 form a structure of chemically segregated, nanoscale domains, which appear significantly more pronounced for Mn0.1Ni0.9Cr2S4. All materials exhibit similar, promising thermal conductivities around 2.0 W m−1 K−1, with Seebeck coefficients ranging from −55 to −65 μV K−1. Only the electrical conductivity is noticeably influenced by the substitutions, with the highest value of 504 S cm−1 obtained for the pristine material, and subsequently declining for both substituted phases.

Various electrode materials are considered for sodium-ion batteries (SIBs) and one important prerequisite for developments of SIBs is a detailed understanding about charge storage mechanisms. Herein, we present a rigorous study about Na storage properties of ultra-small Fe3S4 nanoparticles, synthesized applying a solvothermal route, which exhibit a very good electrochemical performance as anode material for SIBs. A closer look into electrochemical reaction pathways on the nanoscale, utilizing synchrotron-based X-ray diffraction and X-ray absorption techniques, reveals a complicated conversion mechanism. Initially, separation of Fe3S4 into nanocrystalline intermediates occurs accompanied by reduction of Fe3+ to Fe2+ cations. Discharge to 0.1 V leads to formation of strongly disordered Fe0 finely dispersed in a nanosized Na2S matrix. The resulting volume expansion leads to a worse long-term stability in the voltage range 3.0-0.1 V. Adjusting the lower cut-off potential to 0.5 V, crystallization of Na2S is prevented and a completely amorphous intermediate stage is formed. Thus, the smaller voltage window is favorable for long-term stability, yielding highly reversible capacity retention, e.g., 486 mAh g-1 after 300 cycles applying 0.5 A g-1 and superior coulombic efficiencies >99.9%. During charge to 3.0 V, Fe3S4 with smaller domains are reversibly generated in the 1st cycle, but further cycling results in loss of structural long-range order, whereas the local environment resembles that of Fe3S4 in subsequent charged states. Electrokinetic analyses reveal high capacitive contributions to the charge storage, indicating shortened diffusion lengths and thus, redox reactions occur predominantly at surfaces of nanosized conversion products.

Metallic spinel-type CuCo$_{2}$S$_{4}$ nanoparticles were deposited on nanocrystalline TiO$_{2}$ (P25®), forming heterostructure nanocomposites. The nanocomposites were characterized in detail by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), nitrogen sorption (BET) and UV/Vis spectroscopy. Variation of the CuCo$_{2}$S$_{4}$:TiO$_{2}$ ratio to an optimum value generated a catalyst which shows a very high photocatalytic H$_{2}$ production rate at neutral pH of 32.3 µmol/h (0.72 mLh$^{–1}$), which is much larger than for pure TiO$_{2}$ (traces of H$_{2}$). The catalyst exhibits an extraordinary long-term stability and after 70 h irradiation time about 2 mmol H$_{2}$ were generated. An increased light absorption and an efficient charge separation for the sample with the optimal CuCo$_{2}$S$_{4}$:TiO$_{2}$ ratio is most probably responsible for the high catalytic activity.

Metallic spinel‐type CuCo 2 S 4 nanoparticles were deposited on nanocrystalline TiO 2 (P25®), forming heterostructure nanocomposites. The nanocomposites were characterized in detail by X‐ray powder diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM), nitrogen sorption (BET) and UV/Vis spectroscopy. Variation of the CuCo 2 S 4 :TiO 2 ratio to an optimum value generated a catalyst which shows a very high photocatalytic H 2 production rate at neutral pH of 32.3 µmol/h (0.72 mL h –1 ), which is much larger than for pure TiO 2 (traces of H 2 ). The catalyst exhibits an extraordinary long‐term stability and after 70 h irradiation time about 2 mmol H 2 were generated. An increased light absorption and an efficient charge separation for the sample with the optimal CuCo 2 S 4 :TiO 2 ratio is most probably responsible for the high catalytic activity.

The influence of sintering parameters on the physical properties and the chemical structure of rhombohedral Cr2S3 (rh‐Cr2S3) is investigated using high pressures and high temperatures. The densification of the powder is performed by applying the high‐pressure field‐assisted sintering technique/spark plasma sintering. Using a titanium–zirconium–molybdenum (TZM) alloy as sintering tool, it is possible to increase the magnitude of the applied pressure to several hundred MPa at temperatures as high as 1223 K. A relative density of up to 99.9% is achieved at a sintering temperature of 1223 K and a pressure of 395 MPa. The presence of phase‐pure rh‐Cr2S3 is proven by X‐ray diffraction analysis and transmission electron microscopy. The Seebeck coefficients of the self‐doped samples change drastically with the sintering temperatures ranging between −650 and −350 μV K−1. The densities and the thermal conductivities of the sintered samples increase with increasing sintering temperatures. The electrical conductivity is largely increased compared with the thermal conductivity potentially due to the current‐assisted high‐pressure sintering.

The occurrence of a unique 3D nanoscale network in Ni–Cr–S, treatedviaspark-plasma sintering, was discovered with a variety ofex situandin situTEM and XRD techniques.

Structural properties of the thermoelectric materials CuCrS2 and CuxCrS2 on different length scales.