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Instruments / Technical Area	Publication Details	Published
I11-High Resolution Powder Diffraction	Structural investigation of the temperature-stable relaxor dielectric Ba0.8Ca0.2TiO3-Bi(Mg0.5Ti0.5)O3 M. Cabral , A. P. Brown , J. Bultitude , A. Britton , R. Brydson , Teresa Roncal-Herrero , D. A. Hall , S. J. Milne , A. M. Rappe , D. C. Sinclair , J. Zhang , Y. Li Journal Of The European Ceramic Society 4 DOI: 10.1016/j.jeurceramsoc.2022.09.039 Open Access Show Abstract ▼ Abstract: Aberration corrected scanning transmission electron microscopy (STEM) and electron diffraction have been used to disclose local structure and nano-chemistry in a Ca modified BaTiO3-Bi(Mg0.5Ti0.5)O3 relaxor dielectric ceramic which exhibits high and near-invariant relative permittivity over a wide temperature range. High-resolution, synchrotron X-ray diffraction indicated a globally cubic structure (Pm ̅ m), but direct atomic-scale imaging by STEM revealed local tetragonal distortions. Nanopolar clusters were identified from B-site atomic displacement vectors measured relative to oxygen ion positions along <100> and <110> zone axes of integrated differential phase contrast (iDPC) STEM images, highlighting cluster sizes of 2-5 nm. Chemical analysis by STEM-energy dispersive X-ray spectroscopy and full pattern refinements of X-ray powder diffraction data each implied high levels of Bi vacancies within the matrix. The possibility that these A-site vacancies modulate the nanopolar structure and promote flattening of the permittivity-temperature response in this class of dielectric is discussed.	Sep 2022
I22-Small angle scattering & Diffraction	"On demand" triggered crystallization of CaCO3 from solute precursor species stabilized by the water-in-oil microemulsion Tomasz M. Stawski , Teresa Roncal-Herrero , Alejandro Fernandez-Martinez , Adriana Matamoros Veloza , Roland Kröger , Liane G. Benning Physical Chemistry Chemical Physics 7 DOI: 10.1039/C8CP00540K Diamond Proposal Number(s): [8742] Open Access Show Abstract ▼ Abstract: Can we control the crystallization of solid CaCO3 from supersaturated aqueous solutions and thus mimic a natural process predicted to occur in living organisms that produce biominerals? Here we show how we achieved this by confining the reaction between Ca2+ and CO32− ions to the environment of nanosized water cores of water-in-oil microemulsions, in which the reaction between the ions is controlled by the intermicellar exchange processes. Using a combination of in situ small-angle X-ray scattering, high-energy X-ray diffraction, and low-dose liquid-cell scanning transmission electron microscopy, we elucidate how the presence of micellar interfaces leads to the formation of a solute CaCO3 phase/species that can be stabilized for extended periods of time inside micellar water nano-droplets. The nucleation and growth of any solid CaCO3 polymorph, including the amorphous phase, from such nano-droplets is prevented despite the fact that the water cores in the used microemulsion are highly supersaturated with respect to all known calcium carbonate solid phases. On the other hand the presence of the solute CaCO3 phase inside of the water cores decreases the rigidity of the micellar surfactant/water interface, which promotes the aggregation of micelles and the formation of large (>2 μm in diameter) globules. The actual precipitation and crystallization of solid CaCO3 could be triggered “on-demand” through the targeted removal of the organic–inorganic interface and hence the destabilization of globules carrying the CaCO3 solute.	May 2018
I22-Small angle scattering & Diffraction	The role of Mg in the crystallization of monohydrocalcite Juan Diego Rodriguez Blanco , Sam Shaw , Pieter Bots , Teresa Roncal-Herrero , Liane G Benning Geochimica Et Cosmochimica Acta 127, 204 - 220 DOI: 10.1016/j.gca.2013.11.034 Show Abstract ▼ Abstract: Monohydrocalcite is a member of the carbonate family which forms in Mg-rich environments at a wide range of Mg/Ca ratios Mg2+aq/Ca2+aq¡Ý0.17<65. Although found in modern sedimentary deposits and as a product of biomineralization, there is a lack of information about its formation mechanisms and about the role of Mg during its crystallization. In this work we have quantitatively assessed the mechanism of crystallization of monohydrocalcite through in situ synchrotron-based small and wide angle X-ray scattering (SAXS/WAXS) and off-line spectroscopic, microscopic and wet chemical analyses. Monohydrocalcite crystallizes via a 4-stage process beginning with highly supersaturated solutions from which a Mg-bearing, amorphous calcium carbonate (ACC) precursor precipitates. This precursor crystallizes to monohydrocalcite via a nucleation-controlled reaction in stage two, while in stage three it is further aged through Ostwald-ripening at a rate of 1.8 ¡À 0.1 nm/h1/2. In stage four, a secondary Ostwald ripening process (66.3 ¡À 4.3 nm/h1/2) coincides with the release of Mg from the monohydrocalcite structure and the concomitant formation of minor hydromagnesite. Our data reveal that monohydrocalcite can accommodate significant amounts of Mg in its structure (¦ÖMgCO3 = 0.26) and that its Mg content and dehydration temperature are directly proportional to the saturation index for monohydrocalcite (SIMHC) immediately after mixing the stock solutions. However, its crystallite and particle size are inversely proportional to these parameters. At high supersaturations (SIMHC = 3.89) nanometer-sized single crystals of monohydrocalcite form, while at low values (SIMHC = 2.43) the process leads to low-angle branching spherulites. Many carbonates produced during biomineralization form at similar conditions to most synthetic monohydrocalcites, and thus we hypothesize that some calcite or aragonite deposits found in the geologic record that have formed at high Mg/Ca ratios could be secondary in origin and may have originally formed via a metastable monohydrocalcite intermediate.	Dec 2013
I22-Small angle scattering & Diffraction	Mechanistic insights into the crystallization of amorphous calcium carbonate (ACC) Pieter Bots , Liane G. Benning , Juan Diego Rodriguez Blanco , Teresa Roncal-Herrero , Samuel Shaw Crystal Growth & Design 12 (7) DOI: 10.1021/cg300676b Diamond Proposal Number(s): [57701] Show Abstract ▼ Abstract: Many organisms use amorphous calcium carbonate (ACC) during crystalline calcium carbonate biomineralization, as a means to control particle shape/size and phase stability. Here, we present an in situ small- and wide-angle X-ray scattering (SAXS/WAXS) study of the mechanisms and kinetics of ACC crystallization at rapid time scales (seconds). Combined with offline solid and solution characterization, we show that ACC crystallizes to vaterite via a three-stage process. First, hydrated and disordered ACC forms, then rapidly transforms to more ordered and dehydrated ACC; in conjunction with this, vaterite forms via a spherulitic growth mechanism. Second, when the supersaturation of the solution with respect to vaterite decreases sufficiently, the mechanism changes to ACC dissolution and vaterite crystal growth. The third stage is controlled by Ostwald ripening of the vaterite particles. Combining this information with previous studies, allowed us to develop a mechanistic understanding of the abiotic crystallization process from ACC to vaterite and all the way to calcite. We propose this is the underlying abiotic mechanism for calcium carbonate biomineralization from ACC. This process is then augmented or altered by organisms (e.g., using organic compounds) to form intricate biominerals. This study also highlights the applicability of in situ time-resolved SAXS/WAXS to study rapid crystallization reactions.	May 2012
I22-Small angle scattering & Diffraction	The role of pH and Mg on the stability and crystallization of amorphous calcium carbonate J. D. Rodriguez-Blanco , S. Shaw , P. Bots , T. Roncall-Herrero , L. G. Benning Journal Of Alloys And Compounds 536 (1) DOI: 10.1016/j.jallcom.2011.11.057 Show Abstract ▼ Abstract: The effects of pH and Mg on the crystallization of amorphous calcium carbonate (ACC) to vaterite and/or calcite were studied using a combination of in situ time resolved synchrotron-based techniques and electron microscopy. The experiments showed that Mg increased the stability of ACC and favoured the formation of calcite over vaterite. A neutral (∼7) starting pH during mixing promoted the transformation of ACC into calcite via a dissolution/reprecipitation mechanism. Conversely, when ACC formed in a solution that started with a high initial pH (∼11.5), the transformation to calcite occurred via metastable vaterite, which formed via a spherulitic growth mechanism. In a second stage this vaterite transformed to calcite via a surface-controlled dissolution and recrystallization mechanism. These crystallization pathways can be explained as a consequence of the pH-dependent composition, local structure, stability and dissolution rates of ACC.	Nov 2011

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