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1. Persistent photoconductivity in barium titanate

   https://doi.org/10.1063/5.0075484  

   Pansegrau, Christopher; McCluskey, Matthew D. (March 2022, Journal of Applied Physics)

   Annealed bulk crystals of barium titanate (BaTiO₃) exhibit persistent photoconductivity (PPC) at room temperature. Samples were annealed in a flowing gas of humid argon and hydrogen, with a higher flow rate corresponding to larger PPC. When exposed to sub-bandgap light, a broad infrared (IR) absorption peak appears at 5000 cm⁻¹(2  μm), attributed to polaronic or free-carrier absorption from electrons in the conduction band. Along with the increased IR absorption, electrical resistance is reduced by a factor of approximately two. The threshold photon energy for PPC is 2.9 eV, similar to the case of SrTiO₃. This similarity suggests that the mechanisms are similar: an electron in substitutional hydrogen (H_O) is photoexcited into the conduction band, causing the proton to leave the oxygen vacancy and attach to a host oxygen atom. The barrier to recover to the ground state is large such that PPC persists at room temperature. 

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2. Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography

   https://doi.org/10.1016/j.epsl.2019.115751  

   Geyman, Ben M.; Ptacek, Jamie L.; LaVigne, Michèle; Horner, Tristan J. (November 2019, Earth and Planetary Science Letters)
3. Nucleation pathways in barium silicate glasses

   https://doi.org/10.1038/s41598-020-79749-2  

   McKenzie, Matthew E.; Deng, Binghui; Van Hoesen, D. C.; Xia, Xinsheng; Baker, David E.; Rezikyan, Aram; Youngman, Randall E.; Kelton, K. F. (December 2021, Scientific Reports)

   null (Ed.)

   Abstract Nucleation is generally viewed as a structural fluctuation that passes a critical size to eventually become a stable emerging new phase. However, this concept leaves out many details, such as changes in cluster composition and competing pathways to the new phase. In this work, both experimental and computer modeling studies are used to understand the cluster composition and pathways. Monte Carlo and molecular dynamics approaches are used to analyze the thermodynamic and kinetic contributions to the nucleation landscape in barium silicate glasses. Experimental techniques examine the resulting polycrystals that form. Both the modeling and experimental data indicate that a silica rich core plays a dominant role in the nucleation process. 

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4. Barium and barite dynamics in Antarctic streams

   https://doi.org/10.1130/G45048.1  

   Saelens, Elsa; Gardner, Christopher B.; Welch, Kathleen A.; Welch, Susan A.; Lyons, W. Berry (August 2018, Geology)
5. 3D zoning of barium in alkali feldspar

   https://doi.org/10.2138/am-2022-8139  

   Lubbers, Jordan; Kent, Adam; Meisenheimer, Douglas; Wildenschild, Dorthe (February 2023, American Mineralogist)

   Abstract Interpretation of chemical zoning within igneous minerals is critical to many petrologic studies. Zoning in minerals, however, is commonly observed in thin sections or grain mounts, which are random 2D slices of a 3D system. Use of these 2D sections to infer 3D geometries requires a set of assumptions, often not directly tested, introduces several issues, and results in partial loss of zoning information. Computed X-ray microtomography (microCT) offers a way to assess 3D zoning in minerals at high resolution. To observe 3D mineral zoning using microCT, however, requires that zoning is observable as differences in X-ray attenuation. Sanidine, with its affinity for Ba in the crystal lattice, can display large, abrupt variations in Ba that are related to various magma reservoir processes. These changes in Ba also significantly change the X-ray attenuation coefficient of sanidine, allowing for discrete mineral zones to be mapped in 3D using microCT. Here we utilize microCT to show 3D chemical zoning within natural sanidines from a suite of volcanic eruptions throughout the geologic record. We also show that changes in microCT grayscale in sanidine are largely controlled by changes in Ba. Starting with 3D mineral reconstructions, we simulate thin-section making by generating random 2D slices across a mineral zone to show that slicing orientation alone can drastically change the apparent width and slope of composition transitions between different zones. Furthermore, we find that chemical zoning in sanidine can commonly occur in more complex geometries than the commonly interpreted concentric zoning patterns. Together, these findings have important implications for methodologies that rely on the interpretation of chemical zoning within minerals and align with previously published numerical models that show how chemical gradient geometries are affected by random sectioning during common sample preparation methods (e.g., thin sections and round mounts). 

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