Growth and structure of CaCO3

Organisms often employ non-classical crystallisation mechanisms to create the remarkable materials that are biominerals. These materials often surpass their synthetic counterparts in terms of physical properties, morphologies and structural organisation. The non-classical mechanisms employed include the controlled formation, transition and release of amorphous precursor material, and the oriented attachment/ nucleation of nano sized particulates. Combined, these strategies are capable of generating hierarchically ordered superstructures. Both of these mechanisms operate under ambient conditions in a physically delimited environment of body fluids, which enables precise regulation of the solution composition. This thesis describes a range of biomimetic studies which have investigated key aspects in the formation and structural organization of calcium carbonate. Of interest were the influence of additives and physical confinement on the formation and transformation of amorphous calcium carbonate (ACC). The studies revealed that both of these factors play key roles in controlling ACC crystallisation. Additives which inhibit crystallisation in solution can accelerate transformation of ACC in the solid state. This effect was observed for all of the larger molecules examined, while the small molecules retarded crystallisation in both solution and the solid state. Investigation of ACC crystallisation in confinement, in turn, demonstrated that ACC dehydrates prior to crystallizing even in solution, and that nucleation of the first crystal phase in solution must occur by dissolution/ reprecipitation. Studies were also performed to characterise the “ammonia diffusion method” which is widely used in the precipitation of calcium carbonate. Despite this, virtually nothing is known about the changes in solution conditions which occur during this process. The analysis showed that the supersaturation remains relatively high and constant throughout most of the process, which potentially enables multiple nucleation events to occur in a single experiment. These results were then used to develop a one pot method which offers comparable reaction conditions. Finally, Bragg coherent diffraction imaging (BCDI) was used to characterise calcite crystals precipitated on self-assembled monolayers (SAM), where these provide a mimic of the organic matrices used to control crystallisation in organisms. Initial observations of the growth and dissolution of calcite by BCDI allowed the visualization of the 3D dislocation network present within a single crystal. Examination of crystals grown on SAMs, in contrast, showed that a build-up strain causes the formation of a single dislocation loop, where this is correlated with the morphological development of the crystal

Rapid Screening of Calcium Carbonate Precipitation in the Presence of Amino Acids: Kinetics, Structure, and Composition

Soluble additives are widely used to control crystallization, leading to a definition of properties including size, morphology, polymorph, and composition. However, because of the number of potential variables in these experiments, it is typically extremely difficult to identify reaction conditions—as defined by solution compositions, temperatures, and combinations of additives—that give the desired product. This article introduces a high-throughput methodology which addresses this challenge and enables the streamlined preparation and characterization of crystalline materials. Using calcium carbonate precipitated in the presence of selected amino acids as a model system, we use well plates as microvolume crystallizers, and an accurate liquid-handling pipetting workstation for sample preparation. Following changes in the solution turbidity using a plate reader delivers information about the reaction kinetics, while semiautomated scanning electron microscopy, powder X-ray diffraction, and Raman microscopy provide structural information about the library of crystalline products. Of particular interest for the CaCO3 system is the development of fluorescence-based protocols which rapidly evaluate the amounts of the additives occluded within the crystals. Together, these methods provide a strategy for efficiently screening a broad reaction space, where this can both accelerate the ability to generate crystalline materials with target properties and develop our understanding of additive-directed crystallization

A lathe system for micrometre-sized cylindrical sample preparation at room and cryogenic temperatures

A simple two-spindle based lathe system for the preparation of cylindrical samples intended for X-ray tomography is presented. The setup can operate at room temperature as well as under cryogenic conditions, allowing the preparation of samples down to 20 and 50 µm in diameter, respectively, within minutes. Case studies are presented involving the preparation of a brittle biomineral brachiopod shell and cryogenically fixed soft brain tissue, and their examination by means of ptychographic X-ray computed tomography reveals the preparation method to be mainly free from causing artefacts. Since this lathe system easily yields near-cylindrical samples ideal for tomography, a usage for a wide variety of otherwise challenging specimens is anticipated, in addition to potential use as a time- and cost-saving tool prior to focused ion-beam milling. Fast sample preparation becomes especially important in relation to shorter measurement times expected in next-generation synchrotron sources

Mechanical adaptation of brachiopod shells via hydration-induced structural changes.

The function-optimized properties of biominerals arise from the hierarchical organization of primary building blocks. Alteration of properties in response to environmental stresses generally involves time-intensive processes of resorption and reprecipitation of mineral in the underlying organic scaffold. Here, we report that the load-bearing shells of the brachiopod Discinisca tenuis are an exception to this process. These shells can dynamically modulate their mechanical properties in response to a change in environment, switching from hard and stiff when dry to malleable when hydrated within minutes. Using ptychographic X-ray tomography, electron microscopy and spectroscopy, we describe their hierarchical structure and composition as a function of hydration to understand the structural motifs that generate this adaptability. Key is a complementary set of structural modifications, starting with the swelling of an organic matrix on the micron level via nanocrystal reorganization and ending in an intercalation process on the molecular level in response to hydration

Super‐Resolution Microscopy Reveals Shape and Distribution of Dislocations in Single‐Crystal Nanocomposites

With their potential to offer new properties, single crystals containing nanoparticles provide an attractive class of nanocomposite materials. However, to fully profit from these, it is essential that we can characterise their 3D structures, identifying the locations of individual nanoparticles, and the defects present within the host crystals. Using calcite crystals containing quantum dots as a model system, we here use 3D stochastic optical reconstruction microscopy (STORM) to locate the positions of the nanoparticles within the host crystal. The nanoparticles are shown to preferentially associate with dislocations in a manner previously recognised for atomic impurities, rendering these defects visible by STORM. Our images also demonstrate that the types of dislocations formed at the crystal/substrate interface vary according to the nucleation face, and dislocation loops are observed that have entirely different geometries to classic misfit dislocations. This approach offers a rapid, easily accessed, and non‐destructive method for visualising the dislocations present within crystals, and gives insight into the mechanisms by which additives become occluded within crystals

Amino Acid Assisted Incorporation of Dye Molecules within Calcite Crystals

Biomineralisation processes invariably occur in the presence of multiple organic additives, which act in combination to give exceptional control over structures and properties. However, few synthetic studies have investigated the cooperative effects of soluble additives. This work addresses this challenge and focuses on the combined effects of amino acids and coloured dye molecules. The experiments demonstrate that strongly coloured calcite crystals only form in the presence of Brilliant Blue R (BBR) and four of the seventeen soluble amino acids, as compared with almost colourless crystals using the dye alone. The active amino acids are identified as those which themselves effectively occlude in calcite, suggesting a mechanism where they can act as chaperones for individual molecules or even aggregates of dyes molecules. These results provide new insight into crystal–additive interactions and suggest a novel strategy for generating materials with target properties

Characterising Lithium-Ion Electrolytes via Operando Raman Microspectroscopy

Knowledge of electrolyte transport and thermodynamic properties in Li-ion and ”beyond Li-ion” technologies is vital for their continued development and success. Here, we present a method for fully characterising electrolyte systems. By measuring the electrolyte concentration gradient over time via operando Raman microspectroscopy, in tandem with potentiostatic electrochemical impedance spectroscopy, the Fickian ”apparent” diffusion coefficient, transference number, thermodynamic factor, ionic conductivity and resistance of charge-transfer were quantified within a single experimental setup. Using lithium bis(fluorosulfonyl)imide (LiFSI) in tetraglyme (G4) as a model system, our study provides a visualisation of the electrolyte concentration gradient; a method for determining key electrolyte properties, and a necessary technique for correlating intermolecular electrolyte structure with the described transport and thermodynamic properties.</div

A Red Phosphorus-Graphite Anode for K-ion Batteries

Red phosphorus (RP) is a promising anode material for potassium-ion batteries because of its theoretical capacity of 865mAhg–1 delivered at an average potential of 0.5V vs K+/K. However, its alloy reactionto form KP entails a volume expansion of 162% resulting in severe stresses that lead to SEI and electrode fracture, loss of electric contact, and ultimately reduced cycle life. Moreover, its low electronic conductivity (10-14 Scm–1) limits rate capability. Here, we report a RP-graphite composite prepared by a two step ball milling procedure to control particle size and optimize carbon coating. Electrodes prepared with the composites achieve high capacity (723mAhg–1) at C/20 and retaining 75% at 5C. It also shows very good cycling stability, retaining more than 96% of the capacity after 100 cycles at 1C.</div

Nanoscale crystal grain characterization: Via linear polarization X-ray ptychography

X-ray linear dichroism and X-ray birefringence microscopy are yet to be fully utilized as instruments in the microstructural characterization of crystalline materials. Here, we demonstrate analyser-free X-ray linear dichroism microscopy using spectroscopic hard X-ray ptychography. First experiments enabled a spectroscopic and microstructural characterisation of polycrystalline vanadium pentoxide on the nanoscale, outside of diffraction-contrast based methods. This journal is © The Royal Society of Chemistry.ISSN:1359-7345ISSN:1364-548