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1. On comparison of luminescence properties of La ₂ Zr ₂ O ₇ and La ₂ Hf ₂ O ₇ nanoparticles

   https://doi.org/10.1111/jace.16693  

   Gupta, Santosh K.; Abdou, Maya; Ghosh, Partha S.; Zuniga, Jose P.; Manoharan, Ezhilarasan; Kim, HyeongJun; Mao, Yuanbing (July 2019, Journal of the American Ceramic Society)

   Abstract Unveiling the underlying mechanisms of properties of functional materials, including the luminescence differences among similar pyrochlores A₂B₂O₇, opens new gateways to select proper hosts for various optoelectronic applications by scientists and engineers. For example, although La₂Zr₂O₇(LZO) and La₂Hf₂O₇(LHO) pyrochlores have similar chemical compositional and crystallographic structural features, they demonstrate different luminescence properties both before and after doped with Eu³⁺ions. Based on our earlier work, LHO‐based nanophosphors display higher photo‐ and radioluminescence intensity, higher quantum efficiency, and longer excited state lifetime compared to LZO‐based nanophosphors. Moreover, under electronic O²⁻→Zr⁴⁺/Hf⁴⁺transition excitation at 306 nm, undoped LHO nanoparticles (NPs) have only violet blue emission, whereas LZO NPs show violet blue and red emissions. In this study, we have combined experimental and density functional theory (DFT) based theoretical calculation to explain the observed results. First, we calculated the density of state (DOS) based on DFT and studied the energetics of ionized oxygen vacancies in the band gaps of LZO and LHO theoretically, which explain their underlying luminescence difference. For Eu³⁺‐doped NPs, we performed emission intensity and lifetime calculations and found that the LHOE NPs have higher host to dopant energy transfer efficiency than the LZOE NPs (59.3% vs 24.6%), which accounts for the optical performance superiority of the former over the latter. Moreover, by corroborating our experimental data with the DFT calculations, we suggest that the Eu³⁺doping states in LHO present at exact energy position (both in majority and minority spin components) where oxygen defect states are located unlike those in LZO. Lastly, both the NPs show negligible photobleaching highlighting their potential for bioimaging applications. This current report provides a deeper understanding of the advantages of LHO over LZO as an advanced host for phosphors, scintillators, and fluoroimmunoassays. 

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2. Transparent polycrystalline Gd ₂ Hf ₂ O ₇ ceramics

   https://doi.org/10.1111/jace.15550  

   Chen, Ching‐Fong; Brennecka, Geoff L.; Synowicki, R. A.; Tegtmeier, Eric L.; Brand, Michael J.; Montalvo, J. D.; Ivy, Jacob; Cherepy, Nerine J.; Seeley, Zach; Payne, Steven A. (September 2018, Journal of the American Ceramic Society)
3. a -axis YBa ₂ Cu ₃ O _7−x /PrBa ₂ Cu ₃ O _7−x /YBa ₂ Cu ₃ O _7−x trilayers with subnanometer rms roughness

   https://doi.org/10.1063/5.0034648  

   Suyolcu, Y. Eren; Sun, Jiaxin; Goodge, Berit H.; Park, Jisung; Schubert, Jürgen; Kourkoutis, Lena F.; Schlom, Darrell G. (February 2021, APL Materials)

   null (Ed.)
4. Antiferromagnetic Ordering in Quasi-One-Dimensional FeBi ₄ S ₇

   https://doi.org/10.1021/acs.chemmater.4c00249  

   Campbell, Ian; Garlea, Vasile Ovidiu; Zhang, Qiang; Adhikari, Yuwaraj; Xiong, Peng; Yutronkie, Nathan J.; Rogalev, Andrei; Shatruk, Michael (April 2024, Chemistry of Materials)

   We report a detailed study of the synthesis, composition, magnetic structure, and transport properties of a quasi-one-dimensional antiferromagnet FeBi4S7 that contains chains of edge-sharing FeS6 octahedra. High-resolution powder X-ray diffraction (PXRD) analysis, aided by variation of synthetic conditions, suggests that the true formula of the material is Fe1.2Bi3.8S7, due to the minor substitution of Fe into Bi sites. This finding is in agreement with crystal structure refinement from neutron powder diffraction data as well as with the small band gap of 0.23 eV determined from electrical transport measurements. Analysis of the neutron diffraction pattern collected below the antiferromagnetic ordering temperature of 64 K revealed ferromagnetic coupling between the Fe moments in the chains of FeS6 octahedra. The overall ordering, however, is antiferromagnetic due to the antiparallel arrangement of moments on neighboring chains. The collinear spin arrangement is described by a k-vector (1, 0, 1/2), which indicates doubling of the unit cell in the c direction and the loss of the C-centering translation as compared to the nuclear cell. The ferromagnetic nature of the sulfidebridged chains of Fe2+ ions in FeBi4S7, in contrast to the antiferromagnetic coupling between Fe moments in compounds with similar structural fragments, can be justified by the analysis of metric parameters that characterize the Fe−S bonding in these materials. 

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5. The crystal and defect structures of polar KBiNb ₂ O ₇

   https://doi.org/10.1039/d1dt04064b  

   Mallick, Subhadip; Zhang, Weiguo; Batuk, Maria; Gibbs, Alexandra S.; Hadermann, Joke; Halasyamani, P. Shiv; Hayward, Michael A. (February 2022, Dalton Transactions)

   KBiNb 2 O 7 was prepared from RbBiNb 2 O 7 by a sequence of cation exchange reactions which first convert RbBiNb 2 O 7 to LiBiNb 2 O 7 , before KBiNb 2 O 7 is formed by a further K-for-Li cation exchange. A combination of neutron, synchrotron X-ray and electron diffraction data reveal that KBiNb 2 O 7 adopts a polar, layered, perovskite structure (space group A 11 m ) in which the BiNb 2 O 7 layers are stacked in a (0, ½, z ) arrangement, with the K + cations located in half of the available 10-coordinate interlayer cation sites. The inversion symmetry of the phase is broken by a large displacement of the Bi 3+ cations parallel to the y -axis. HAADF-STEM images reveal that KBiNb 2 O 7 exhibits frequent stacking faults which convert the (0, ½, z ) layer stacking to (½, 0, z ) stacking and vice versa , essentially switching the x - and y -axes of the material. By fitting the complex diffraction peak shape of the SXRD data collected from KBiNb 2 O 7 it is estimated that each layer has approximately a 9% chance of being defective – a high level which is attributed to the lack of cooperative NbO 6 tilting in the material, which limits the lattice strain associated with each fault. 

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