Search

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. [ABSTRACT FROM AUTHOR]

The precipitation of struvite, a magnesium ammonium phosphate hexahydrate (MgNH4PO4 · 6H2O) mineral, from wastewater is a promising method for recovering phosphorous. While this process is commonly used in engineered environments, our understanding of the underlying mechanisms responsible for the formation of struvite crystals remains limited. Specifically, indirect evidence suggests the involvement of an amorphous precursor and the occurrence of multi-step processes in struvite formation, which would indicate non-classical paths of nucleation and crystallization. In this study, we use synchrotron-based in situ x-ray scattering complemented by cryogenic transmission electron microscopy to obtain new insights from the earliest stages of struvite formation. The holistic scattering data captured the structure of an entire assembly in a time-resolved manner. The structural features comprise the aqueous medium, the growing struvite crystals, and any potential heterogeneities or complex entities. By analysing the scattering data, we found that the onset of crystallization causes a perturbation in the structure of the surrounding aqueous medium. This perturbation is characterized by the occurrence and evolution of Ornstein-Zernike fluctuations on a scale of about 1 nm, suggesting a non-classical nature of the system. We interpret this phenomenon as a liquid-liquid phase separation, which gives rise to the formation of the amorphous precursor phase preceding actual crystal growth of struvite. Our microscopy results confirm that the formation of Mg-struvite includes a short-lived amorphous phase, lasting >10 s. [ABSTRACT FROM AUTHOR]

Phase transformations during high-energy ball milling, a tool of mechanochemistry, are interesting due to the possible production of metastable phases without the need for artificially introducing high temperatures and pressures. In our work, the transformation of calcite to aragonite in an eggshell is studied in detail. The presence of organic material, in either the naturally present eggshell membrane, or artificially supplied L -cysteine, was found to be crucial for the phase transformation to occur, its decomposition leading to a pressure increase necessary for aragonite formation. The presence of sulfur in the organics seems to be crucial, as corroborated by much lower phase transformation extent when utilizing sulfur-free organics for comparison. The degree of the transformation in an eggshell was strongly dependent on the used milling conditions. The optimization was assessed using the Taguchi method, namely using a 44 orthogonal array. The optimized parameters encompassed milling time, sample mass, milling speed and duration of breaks and it was shown that sample mass has a decisive effect on the amount of obtained aragonite. Under the most efficient conditions, 73.7% of aragonite was obtained. Prolonging milling until 4 hours further boosts the transformation, reaching 89.9% of aragonite, but further milling leads to the collapse of the aragonite structure and pure calcite was observed after 5 hours. [ABSTRACT FROM AUTHOR]

Transition metal phosphates (TMPs) have attracted interest as materials for (electro-) catalysis, and electrochemistry due to their low-cost, stability, and tunability. In this work, an automated synthesis platform was used for the preparation of transition metal phosphate crystals to efficiently explore the multidimensional parameter space, determining the phase selection, crystal sizes, shapes. By using X-ray diffraction and spectroscopy-based methods and electron microscopy imaging, a complete characterization of the phase stability fields, phase transitions, and crystal morphology/sizes was achieved. In an automated three-reactant synthesis, the individual effect of each reactant species NH4+, M2+, and PO43− on the formation of transition metal phosphate phases: M-struvite NH4MPO4·6H2O, M–phosphate octahydrate M3(PO4)2·8H2O with M = Ni, Co and an amorphous phase, was investigated. The NH4+ concentration dictates the phase composition, morphology, and particle size in the Ni-system (crystalline Ni-struvite versus amorphous Ni–PO4 phase), whereas in the Co-system all reactant species – NH4+, Co2+, and PO43− – influence the reaction outcome equivalently (Co-struvite vs. Co–phosphate octahydrate). The coordination environment for all crystalline compounds and of the amorphous Ni–PO4 phase was resolved by X-ray absorption spectroscopy, revealing matching characteristics to its crystalline analogue, Ni3(PO4)2·8H2O. The automated synthesis turned out to be significantly advantageous for the exploration of phase diagrams due to its simple modularity, facile traceability, and enhanced reproducibility compared to a typical manual synthesis. [ABSTRACT FROM AUTHOR]