More Like this

1. Symmetry-mode analysis for local structure investigations using pair distribution function data

   https://doi.org/10.1107/S1600576723005794  

   Hamilton, Parker K.; Moya, Jaime M.; Hallas, Alannah M.; Morosan, E.; Baral, Raju; Frandsen, Benjamin A. (August 2023, Journal of Applied Crystallography)

   Symmetry-adapted distortion modes provide a natural way of describing distorted structures derived from higher-symmetry parent phases. Structural refinements using symmetry-mode amplitudes as fit variables have been used for at least ten years in Rietveld refinements of the average crystal structure from diffraction data; more recently, this approach has also been used for investigations of the local structure using real-space pair distribution function (PDF) data. Here, the value of performing symmetry-mode fits to PDF data is further demonstrated through the successful application of this method to two topical materials: TiSe 2 , where a subtle but long-range structural distortion driven by the formation of a charge-density wave is detected, and MnTe, where a large but highly localized structural distortion is characterized in terms of symmetry-lowering displacements of the Te atoms. The analysis is performed using fully open-source code within the DiffPy framework via two packages developed for this work: isopydistort , which provides a scriptable interface to the ISODISTORT web application for group theoretical calculations, and isopytools , which converts the ISODISTORT output into a DiffPy -compatible format for subsequent fitting and analysis. These developments expand the potential impact of symmetry-adapted PDF analysis by enabling high-throughput analysis and removing the need for any commercial software. 

   more » « less
2. Ba ₄ RuMn ₂ O ₁₀ : A Noncentrosymmetric Polar Crystal Structure with Disordered Trimers

   https://doi.org/10.1021/acs.chemmater.4c00586  

   Skaggs, Callista M; Siegfried, Peter E; Cho, Jun Sang; Xin, Yan; Garlea, V Ovidiu; Taddei, Keith M; Bhandari, Hari; Croft, Mark; Ghimire, Nirmal J; Jang, Joon I; et al (June 2024, Chemistry of Materials)

   Phase-pure polycrystalline Ba4RuMn2O10 was prepared and determined to adopt the noncentrosymmetric polar crystal structure (space group Cmc21) based on results of second harmonic generation, convergent beam electron diffraction, and Rietveld refinements using powder neutron diffraction data. The crystal structure features zigzag chains of corner-shared trimers, which contain three distorted face-sharing octahedra. The three metal sites in the trimers are occupied by disordered Ru/Mn with three different ratios: Ru1:Mn1 = 0.202(8):0.798(8), Ru2:Mn2 = 0.27(1):0.73(1), and Ru3:Mn3 = 0.40(1):0.60(1), successfully lowering the symmetry and inducing the polar crystal structure from the centrosymmetric parent compounds Ba4T3O10 (T = Mn, Ru; space group Cmca). The valence state of Ru/Mn is confirmed to be +4 according to X-ray absorption near-edge spectroscopy. Ba4RuMn2O10 is a narrow bandgap (∼0.6 eV) semiconductor exhibiting spin-glass behavior with strong magnetic frustration and antiferromagnetic interactions. 

   more » « less
3. Reverberation Mapping of IC 4329A

   https://doi.org/10.3847/1538-4357/acab62  

   Bentz, Misty C.; Onken, Christopher A.; Street, Rachel; Valluri, Monica (February 2023, The Astrophysical Journal)

   Abstract We present the results of a new reverberation mapping campaign for the broad-line active galactic nucleus (AGN) in the edge-on spiral IC 4329A. Monitoring of the optical continuum withV-band photometry and broad emission-line flux variability with moderate-resolution spectroscopy allowed emission-line light curves to be measured for Hβ, Hγ, and Heiiλ4686. We find a time delay of ${16.3}_{-2.3}^{+2.6}$days for Hβ, a similar time delay of ${16.0}_{-2.6}^{+4.8}$days for Hγ, and an unresolved time delay of $-{0.6}_{-3.9}^{+3.9}$days for Heii. The time delay for Hβis consistent with the predicted value from the relationship between AGN luminosity and broad-line region radius, after correction for the ∼2.4 mag of intrinsic extinction at 5100 Å. Combining the measured time delay for Hβwith the broad emission-line width and an adopted value of 〈f〉 = 4.8, we find a central supermassive black hole mass of $M_{\mathrm{BH}}={6.8}_{-1.1}^{+1.2}\times {10}^7$M_⊙. Velocity-resolved time delays were measured across the broad Hβemission-line profile and may be consistent with an “M”-like shape. Modeling of the full reverberation response of Hβwas able to provide only modest constraints on some parameters, but does exhibit agreement with the black hole mass and average time delay. The models also suggest that the AGN structure is misaligned by a large amount from the edge-on galaxy disk. This is consistent with expectations from the unified model of AGNs, in which broad emission lines are expected to be visible only for AGNs that are viewed at relatively face-on inclinations. 

   more » « less
4. Systematic Trends of Transformation Temperatures and Crystal Structure of Ni–Mn–Ga–Fe–Cu Alloys

   https://doi.org/10.1007/s40830-020-00273-3  

   Armstrong, Andrew; Nilsen, Frans; Rames, Michal; Colman, Ross; Vertat, Petr; Kmjec, Tomas; Straka, Ladislav; Mullner, Peter; Heczko, Oleg (March 2020, Shape memory and superelasticity)

   Here we report a systematic research on effects of Fe and Cu upon properties relevant for the magnetic shape memory effect of Ni–Mn–Ga ferromagnetic shape memory alloys. Fe and Cu were identified as elements with potential synergism to increase the martensite transformation temperature of Ni–Mn–Ga magnetic shape memory (MSM) alloys. Eighteen Ni–Mn–Ga–Fe–Cu alloys with different systematic trends in substituting the ternary elements with Cu and Fe have been investigated. We found a method to describe the effectiveness of Ni, Mn, and Cu upon raising the martensitic transformation temperature, lowering the saturation magnetization, and varying the Curie temperature. We find the martensite transformation temperature most influenced by the Ni content, followed by Mn, with a smaller effect of Cu. The saturation magnetization decreases with similar coefficients for Mn and Cu alloying. The Curie temperature monotonously decreases with Mn, but not Cu. The 10M martensite structure is stable for the composition Ni46.5Mn25?XGa25-X-YFe3.5CuY with X and Y range of 0–5.7, and 0.8–3.0. Used in combination with the total e/a, the elemental e/a-ratio gives some insight into the complex behavior of quinary MSM alloys and is a useful method of analyzing MSM alloys for improved functional properties. 

   more » « less
5. Middle Stone Age mineral pigment procurement at Pinnacle Point 5–6 North, Western Cape province, South Africa

   https://doi.org/10.1111/arcm.12694  

   McGrath, James_R; MacDonald, Brandi_L; Stalla, David (June 2021, Archaeometry)

   Abstract We report on a multi‐method sourcing study of 35 mineral pigment artefacts from the Middle Stone Age site of Pinnacle Point 5–6 North (PP5–6 N), dating from about 90–50 ka. The artefacts were analysed and compared with geological samples from seven sources using neutron activation analysis (NAA), and supplemented by data from X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Our preliminary results suggest that the occupants of PP5–6 N likely used at least two local and one currently unidentified and possibly non‐local Fe oxide mineral pigment sources. The mineral pigment artefacts derived from the latter source(s) exhibited manganese (Mn) enrichment with concentrations well above those observed in all sampled source deposits in the study area, suggesting a distinctive formation process. The proportions of the Mn‐enriched mineral pigment artefacts within the PP5–6 N assemblage vary over time, but tend to occur at higher rates in the glacial Marine Isotope Stage (MIS) 4 deposits, which holds potential implications for changes in the use of sources over time, increased mobility or increased exchange during this period. 

   more » « less