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Nanoscale 15(11), 5284 - 5292 (2023). doi:10.1039/D2NR07128B, Gallium oxides are of broad interest due to their wide band gaps and attractive photoelectric properties. Typically, the synthesis of gallium oxide nanoparticles is based on a combination of solvent-based methods and subsequent calcination, but detailed information about solvent based formation processes is lacking, and this limits the tailoring of materials. Here we have examined the formation mechanisms and crystal structure transformations of gallium oxides during solvothermal synthesis using in situ X-ray diffraction. $γ$-Ga$_2$O$_3$ readily forms over a wide range of conditions. In contrast, $β$-Ga$_2$O$_3$ only forms at high temperatures (T > 300 °C), and it is always preceded by $γ$-Ga$_2$O$_3$, indicating that $γ$-Ga$_2$O$_3$ is a crucial part of the formation mechanism of $β$-Ga$_2$O$_3$. The activation energy for formation of $β$-Ga$_2$O$_3$ from $γ$-Ga$_2$O$_3$ is determined to be 90–100 kJ mol$^{−1}$ in ethanol, water and aqueous NaOH based on kinetic modelling of phase fractions obtained from multi-temperature in situ X-ray diffraction data. At low temperatures GaOOH and Ga$_5$O$_7$OH form in aqueous solvent, but these phases are also obtained from $γ$-Ga$_2$O$_3$. Systematic exploration of synthesis parameters such as temperature, heating rate, solvent and reaction time reveal that they all affect the resulting product. In general, the solvent based reaction paths are different from reports on solid state calcination studies. This underlines that the solvent is an active part of the solvothermal reactions and to a high degree determines different formation mechanisms., Published by RSC Publ., Cambridge

The structures of metal ions in solution constitute essential information for obtaining chemical insight spanning from catalytic reaction mechanisms to formation of functional nanomaterials. Here, we explore Zr

Chemical science 13(43), 12883 - 12891 (2022). doi:10.1039/D2SC04522B, The structures of metal ions in solution constitute essential information for obtaining chemical insight spanning from catalytic reaction mechanisms to formation of functional nanomaterials. Here, we explore Zr$^{4+}$ solution structures using X-ray pair distribution function (PDF) analysis across pH (0–14), concentrations (0.1–1.5 M), solvents (water, methanol, ethanol, acetonitrile) and metal sources (ZrCl$_4$, ZrOCl$_2$·8H$_2$O, ZrO(NO$_3$)$_2$·xH$_2$O). In water, [Zr$_4$(OH)$_8$(OH$_2$)$_{16}$]$^{8+}$-tetramers are predominant, while non-aqueous solvents contain monomeric complexes. The PDF analysis also reveals second sphere coordination of chloride counter ions to the aqueous tetramers. The results are reproducible across data measured at three different beamlines at the PETRA-III and MAX IV synchrotron light sources., Published by RSC, Cambridge

The indium oxides, c-In2O3, h-In2O3, InOOH and In(OH)3, constitute an important class of wide band gap semiconductors. Synthesis of any indium oxide phase involves manoeuvring in a complex matrix of process parameters, and some phases are only obtained through controlled phase transformations. Considering the widespread use of indium oxide semiconductors it is restrictive that no coherent picture exists of the formation mechanisms of individual phases and phase transformations between them. Here we access the indium oxide system through solvothermal synthesis and/or powder calcinations, and we use in situ X-ray scattering in combination with thermal analysis to investigate the complex phase relations. This allows us to unravel synthesis pathways for the different indium oxide phases, and the insight is used to develop procedures for scalable continuous flow solvothermal synthesis. Direct formation of crystalline nanomaterials from precursor solutions was observed for In(OH)3, InOOH and cubic c-In2O3, while formation of hexagonal h-In2O3 requires thermal decomposition of InOOH. The in situ X-ray scattering data reveal new phase transformations from In(OH)3 to InOOH, and from InOOH to c-In2O3. Interestingly, solvothermal synthesis conditions facilitate different reactions mechanisms than dry powder calcinations, and both In(OH)3 and InOOH have different transformations under dry and wet conditions. This journal is.

Chemical science tbd, 1-12 (2021). doi:10.1039/D1SC05190C, The atomic structures, and thereby the coordination chemistry, of metal ions in aqueous solution represent a cornerstone of chemistry, since they provide first steps in rationalizing generally observed chemical information. However, accurate structural information about metal ion solution species is often surprisingly scarce. Here, the atomic structures of Ga$^{3+}$ ion complexes were determined directly in aqueous solutions across a wide range of pH, counter anions and concentrations by X-ray pair distribution function analysis and $^{71}$Ga NMR. At low pH ( 12 tetrahedrally coordinated gallium ions surrounded by ordered solvent are observed. The effects of varying either the concentration or counter anion were minimal. The present study provides the first comprehensive structural exploration of the aqueous chemistry of Ga$^{3+}$ ions with atomic resolution, which is relevant for both semiconductor fabrication and medical applications., Published by RSC, Cambridge

Advanced functional materials often contain multiple phases which are (nano)crystalline and/or amorphous. The spatial distribution of these phases and their properties, including nanocrystallite size and shape, often drives material function yet is difficult to obtain with current experimental techniques. This article describes the use of diffraction scattering computed tomography, which maps wide-angle scattering information onto sample space, to address this challenge. The wide-angle scattering signal contains information on both (nano)crystalline and amorphous phases. Rietveld refinement of reconstructed diffraction patterns is employed to determine anisotropic nanocrystal shapes. The background signal from refinements is used to identify contributing amorphous phases through multivariate curve resolution. Thus it is demonstrated that reciprocal space analysis in combination with diffraction scattering computed tomography is a very powerful tool for the complete analysis of complex multiphase materials such as energy devices.

Precursor structures (PSs) in solution are expected to influence both nanocrystal formation mechanisms, as well as crystallization of specific polymorphs. Herein, Group 13 PS structures determined by pair distribution function and extended X-ray absorption fine structure analysis are reported. Corner-sharing octahedral dimers form from the metal nitrates dissolved in either water, isopropanol, or ethanol at room temperature contradicting previous studies that suggested monomers or larger Keggin clusters. Because all crystalline indium oxides have octahedral coordination, crystals can easily nucleate from the observed PSs. Similarly, MOOH (M=Al and Ga) with octahedral M coordination is expected to form readily from the PSs, whereas formation of gamma-M2O3 requires a partial conversion to tetrahedral M coordination. This explains the long-standing observation of initial AlOOH formation as a bottleneck for gamma-Al2O3 synthesis. Different indium polymorphs crystallize from the various solvents, and thus there is no obvious link between the PSs and observed polymorphism.