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1. Solid state synthesis of BiFeO ₃ occurs through the intermediate Bi ₂₅ FeO ₃₉ compound

   https://doi.org/10.1111/jace.19702  

   Wesley, Corrado; Bellcase, Leah; Forrester, Jennifer S.; Dickey, Elizabeth C.; Reaney, Ian M.; Jones, Jacob L. (February 2024, Journal of the American Ceramic Society)

   Abstract The solid‐state synthesis of perovskite BiFeO₃has been a topic of interest for decades. Many studies have reported challenges in the synthesis of BiFeO₃from starting oxides of Bi₂O₃and Fe₂O₃, mainly associated with the development of persistent secondary phases such as Bi₂₅FeO₃₉(sillenite) and Bi₂Fe₄O₉(mullite). These secondary phases are thought to be a consequence of unreacted Fe‐rich and Bi‐rich regions, that is, incomplete interdiffusion. In the present work, in situ high‐temperature X‐ray diffraction is used to demonstrate that Bi₂O₃first reacts with Fe₂O₃to form sillenite Bi₂₅FeO₃₉, which then reacts with the remaining Fe₂O₃to form BiFeO₃. Therefore, the synthesis of perovskite BiFeO₃is shown to occur via a two‐step reaction sequence with Bi₂₅FeO₃₉as an intermediate compound. Because Bi₂₅FeO₃₉and the γ‐Bi₂O₃phase are isostructural, it is difficult to discriminate them solely from X‐ray diffraction. Evidence is presented for the existence of the intermediate sillenite Bi₂₅FeO₃₉using quenching experiments, comparisons between Bi₂O₃behavior by itself and in the presence of Fe₂O₃, and crystal structure examination. With this new information, a proposed reaction pathway from the starting oxides to the product is presented. 

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2. Structural Chemistry of Akdalaite, Al10O14(OH)2, the Isostructural Aluminum Analogue of Ferrihydrite

   https://doi.org/10.3390/cryst9050246  

   Parise, John B.; Xia, Bingying; Simonson, Jack W.; Woerner, William R.; Plonka, Anna M.; Phillips, Brian L.; Ehm, Lars (May 2019, Crystals)

   As part of an effort to characterize clusters and intermediate phases likely to be encountered along solution reaction pathways that produce iron and aluminum oxide-hydroxides from Fe and Al precursors, the complete structure of Al10O14(OH)2 (akdalaite) was determined from a combination of single-crystal X-ray diffraction (SC-XRD) data collected at 100 K to define the Al and O positions, and solid-state nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) data collected at room temperature (~300 K) to precisely determine the nature of hydrogen in the structure. Two different synthesis routes produced different crystal morphologies. Using an aluminum oxyhydroxide floc made from mixing AlCl3 and 0.48 M NaOH, the product had uniform needle morphology, while using nanocrystalline boehmite (Vista Chemical Company Catapal D alumina) as the starting material produced hexagonal plates. Akdalaite crystallizes in the space group P63mc with lattice parameters of a = 5.6244(3) Å and c = 8.8417(3) Å (SC-XRD) and a = 5.57610(2) Å and c = 8.77247(6) Å (NPD). The crystal structure features Al13O40 Keggin clusters. The structural chemistry of akdalaite is nonideal but broadly conforms to that of ferrihydrite, the nanomineral with which it is isostructural. 

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3. Hybrid molecular beam epitaxy of germanium-based oxides

   https://doi.org/10.1038/s43246-022-00290-y  

   Liu, Fengdeng; Truttmann, Tristan K.; Lee, Dooyong; Matthews, Bethany E.; Laraib, Iflah; Janotti, Anderson; Spurgeon, Steven R.; Chambers, Scott A.; Jalan, Bharat (December 2022, Communications Materials)

   Abstract Germanium-based oxides such as rutile GeO 2 are garnering attention owing to their wide band gaps and the prospects of ambipolar doping for application in high-power devices. Here, we present the use of germanium tetraisopropoxide (GTIP), a metal-organic chemical precursor, as a source of germanium for the demonstration of hybrid molecular beam epitaxy for germanium-containing compounds. We use Sn 1- x Ge x O 2 and SrSn 1- x Ge x O 3 as model systems to demonstrate our synthesis method. A combination of high-resolution X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy confirms the successful growth of epitaxial rutile Sn 1- x Ge x O 2 on TiO 2 (001) substrates up to x  = 0.54 and coherent perovskite SrSn 1- x Ge x O 3 on GdScO 3 (110) substrates up to x  = 0.16. Characterization and first-principles calculations corroborate that germanium occupies the tin site, as opposed to the strontium site. These findings confirm the viability of the GTIP precursor for the growth of germanium-containing oxides by hybrid molecular beam epitaxy, thus providing a promising route to high-quality perovskite germanate films. 

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4. Synthesis and characterization of bismuth ferrite particles using a nano-agitator bead mill

   https://doi.org/10.1063/5.0132099  

   Smith, Jr., Lyndon; Shield, Jeffrey; Ahmadi, Zahra; Jeelani, Shaik; Rangari, Vijaya (March 2023, AIP Advances)

   Bismuth ferrite (BiFeO3) nanocomposites were synthesized using a novel nano-agitator bead milling method followed by calcination. Bismuth oxide and iron oxide nanoparticles were mixed in a stoichiometric ratio and milled for 3 h and calcined at 650 °C in air. X-ray diffraction with Rietveld refinement, scanning electron microscopy, and transmission electron microscopy techniques were used to elucidate the structure of BiFeO3. The particle diameter was found to be ∼17 nm. Magnetic and electrical measurements were performed, and these results were compared with those of similar methods. Mostly, BiFeO3 was obtained with minor secondary phase formation. The resulting powder was weakly ferromagnetic with a remnant magnetization of 0.078 emu/g. This can be attributed to residual strain and defects introduced during the milling process. Electrical testing revealed a high leakage current density that is typical of undoped bismuth ferrite. 

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5. Effects of composition and growth parameters on phase formation in multicomponent aluminum garnet crystals

   https://doi.org/10.1107/S2052520622002967  

   Pianassola, Matheus; Alexander, Marlena; Chakoumakos, Bryan; Koschan, Merry; Melcher, Charles; Zhuravleva, Mariya (June 2022, Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials)

   The effects of composition on the phase formation of multicomponent garnet crystals grown via directional solidification by the micro-pulling-down method are studied. A relatively wide range of rare-earth (RE) average ionic radii (AIR) is explored by formulating ten compositions from the system (Lu,Y,Ho,Dy,Tb,Gd) 3 Al 5 O 12 . Crystals were grown at either 0.05 or 0.20 mm min −1 . The hypothesis is that multicomponent compounds with large AIR will form secondary phases as the single-RE aluminum garnets formed by larger Tb 3+ or Gd 3+ ; this will result in crystals of poor optical quality. Crystals with large AIR have a central opaque region in optical microscopy images, which is responsible for their reduced transparency compared to crystals with small AIR. Slow pulling rates suppress the formation of the opaque region in crystals with intermediate AIR. Powder and single-crystal X-ray diffraction and electron probe microanalysis results indicate that the opaque region is a perovskite phase. Scanning electron microscopy and energy dispersive spectroscopy measurements reveal eutectic inclusions at the outer surface of the crystals. The concentration of the eutectic inclusions increases with increasing AIR. 

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