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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Electronic band structure and low-temperature transport properties of the type-I clathrate BA8NIXGE46-X-Y(Royal Soc Chemistry, 2015) Candolfi, C.; Ormeci, A.; Baitinger, M.; Burkhardt, U.; Oeschler, N.; Steglich, F.; Grin, Yu.; Department of Chemistry; Aydemir, Umut; Faculty Member; Department of Chemistry; College of Sciences; 58403We present the evolution of the low-temperature thermodynamic, galvanomagnetic and thermoelectric properties of the type-I clathrate Ba8NixGe46-x-y square(y) with the Ni concentration studied on polycrystalline samples with 0.0 <= x <= 6.0 by means of specific heat, Hall effect, electrical resistivity, thermopower and thermal conductivity measurements in the 2-350 K temperature range and supported by first-principles calculations. The experimental results evidence a 2a x 2a x 2a supercell described in the space group Ia (3) over bard for x <= 1.0 and a primitive unit cell a x a x a (space group Pm (3) over barn) above this Ni content. This concentration also marks the limit between a regime where both electrons and holes contribute to the electrical conduction (x <= 1.0) and a conventional, single-carrier regime (x > 1.0). This evolution is traced by the variations in the thermopower and Hall effect with x. In agreement with band structure calculations, increasing the Ni content drives the system from a nearly-compensated semimetallic state (x = 0.0) towards a narrow-band-gap semiconducting state (x = 4.0). A crossover from an n-type to a p-type conduction occurs when crossing the x = 4.0 concentration i.e. for x = 4.1. The solid solution Ba8NixGe46-x-y square(y) therefore provides an excellent experimental platform to probe the evolution of the peculiar properties of the parent type-I clathrate Ba8Ge43 square(3) upon Ge/Ni substitution and filling up of the vacancies, which might be universal among the ternary systems at low substitution levels.Publication Metadata only CS4GE9 center dot en: a novel compound with [GE-9](4-) clusters - synthesis, crystal structure and vibrational spectra(Wiley-V C H Verlag Gmbh, 2007) Carrillo-Cabrera, Wilder; Kırcalı, Aslıhan; Faessler, Thomas F.; Hoffmann, Stephan D.; Department of Chemistry; Department of Chemistry; Aydemir, Umut; Somer, Mehmet Suat; Faculty Member; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; 58403; 178882Red-orange prismatic crystals of CS4Ge9.en (en = ethyl-enediamine) were obtained via metathesis reaction of an en solution of K4Ge9 with a large excess of CsI. The compound is very sensitive to air and moisture. CS4Ge9.en is not isotypic to Rb4Ge9.en and crystallizes in a new structure type (monoclinic, space group P2(1)/c (No. 14); a = 16.757(3), h = 16.462(3), c = 15.657(2) angstrom, beta = 90.37(1)degrees; Z = 8; Pearson code mP200). The crystal structure comprises two types (A and B) of discrete [Ge-9](4-)units arranged in the motif of a distorted hexagonal close-packing (h.c.p.). In this h.c.p. framework, each tetrahedral hole is filled by one Cs atom and each larger octahedral hole is tilled by a group of one en and two Cs atoms. The topology of the two crystallographically distinct [Ge-9](4-) clusters corresponds to distorted, monocapped tetragonal antiprisms with bond lengths varying in the range 2.551-2.848 angstrom (type A cluster) or in the range 2.538-2.975 angstrom (less regular type B cluster). According to the DTA and TG measurements, CS4Ge9.en decomposes at 378 K under liberation of gaseous ethylenediamine yielding CS4Ge9. The Raman spectra of the title compound were interpreted based on the idealized C-4v symmetry of an isolated [Geg](4-) cluster. The characteristic breathing mode was localized at 222 cm(-1). The results are analyzed and discussed in context with those of the previously reported compounds CS4Ge9, K4Ge9 and Rb4Ge9.en.Publication Metadata only Isotropic zero thermal expansion and local vibrational dynamics in (SC,FE)F-3(American Chemical Society (ACS), 2017) Qin, Feiyu; Chen, Jun; Sanson, Andrea; Wang, Lu; Pan, Zhao; Xu, Jiale; Sun, Chengjun; Ren, Yang; Deng, Jinxia; Yu, Ranbo; Hu, Lei; Snyder, G. Jeffrey; Xing, Xianran; Department of Chemistry; Aydemir, Umut; Faculty Member; Department of Chemistry; College of Sciences; 58403Scandium fluoride (ScF3) exhibits a pronounced negative thermal expansion (NTE), which can be suppressed and ultimately transformed into an isotropic zero thermal expansion (ZTE) by partially substituting Sc with Fe in (Sc0.8Fe0.2)F-3 (Fe20). The latter displays a rather small coefficient of thermal expansion of -0.17 X 10(-6)/K from 300 to 700 K. Synchrotron X-ray and neutron pair distribution functions confirm that the Sc/ Fe-F bond has positive thermal expansion (PTE). Local vibrational dynamics based on extended X-ray absorption fine structure indicates a decreased anisotropy of relative vibration in the Sc/Fe-F bond. Combined analysis proposes a delicate balance between the counteracting effects of the chemical bond PTE and NTE from transverse vibration. The present study extends the scope of isotropic ZTE compounds and, more significantly, provides a complete local vibrational dynamics to shed light on the ZTE mechanism in chemically tailored NTE compounds.Publication Metadata only Nickel−palladium alloy nanoparticles supported on reduced graphene oxide decorated with metallic aluminum nanoparticles (Al-rGO/NiPd): a multifunctional catalyst for the transfer hydrogenation of nitroarenes and olefins using water as a hydrogen source(Royal Soc Chemistry, 2021) Dagalan, Ziya; Behboudikhiavi, Sepideh; Turgut, Muhammet; Sevim, Melike; Kasapoglu, Ahmet Emre; Nisanci, Bilal; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; College of Sciences; 46962We report herein an innovative design and synthesis of a novel multifunctional nanocatalyst for the transfer hydrogenation (TH) of nitroarenes and olefins using water as a hydrogen source and solvent. The presented nanocatalyst is composed of NiPd alloy nanoparticles (NPs) supported on reduced graphene oxide (rGO) decorated with metallic Al NPs (Al-rGO/NiPd). In the catalyst, metallic Al NPs serve as the sacrificing agent for hydrogen generation via the Al-H2O reaction, NiPd NPs act as the catalyst for the transfer of the generated hydrogen to the unsaturated compounds, and rGO functions as both a support material and stabilizer for the NPs. Among all tested catalysts, Al-rGO/Ni40Pd60 nanocatalysts are found to be the most efficient and selective catalysts in the presented TH of nitroarenes (14 examples) and olefins (14 examples) with yields reaching up to 99% under the optimized reaction conditions. Additionally, Al-rGO/Ni40Pd60 nanocatalysts are recyclable catalysts in the TH reactions by catalyzing ten consecutive runs in the TH of nitrobenzene without a significant drop in their initial catalytic activity, which is the first example in this regard. Last but not least, the current transfer hydrogenation protocol provides selectivity for the reduction of only the -NO2 group of nitroarenes bearing iodo or bromo substituents on the same aromatic ring. This study is the first example of a TH protocol that employs an Al-modified nanomaterial serving as both a hydrogen generator and reusable catalyst in water without using any additional hydrogen source.Publication Metadata only Switch of thermal expansions triggered by itinerant electrons in isostructural metal trifluorides(American Chemical Society (ACS), 2022) Qin, Feiyu; Wang, Xiaoying; Hu, Lei; Jia, Ning; Gao, Zhibin; Chen, Jun; Ding, Xiangdong; Sun, Jun; Department of Chemistry; Aydemir, Umut; Faculty Member; Department of Chemistry; College of Sciences; 58403Manageable thermal expansion (MTE) of metal trifluorides can be achieved by introducing local structure distortion (LSD) in the negative thermal expansion ScF3. However, an open issue is why isostructural TiF3, free of LSD, exhibits positive thermal expansion. Herein, a combined analysis of synchrotron X-ray diffraction, X-ray pair distribution function, and rigorous first-principles calculations was performed to reveal the important role of itinerant electrons in mediating soft phonons and lattice dynamics. Metallic TiF3 demonstrates itinerant electrons and a suppressed Gru''neisen parameter gamma -20, while insulating ScF3 absence of itinerant electrons has a considerable gamma -120. With increasing electron doping concentrations in ScF3, soft phonons become hardened and the gamma is repressed significantly, identical to TiF3. The presented results update the thermal expansion transition mechanism in framework structure analogues and provide a practical approach to obtaining MTE without inducing sizable structure distortion.Publication Metadata only Synthesis, crystal structures, and vibrational spectra of novel azidopalladates of the alkali metals cs-2[pd(n-3)(4)] and rb-2[pd(n-3)(4)]center dot 2/3h(2)o(Wiley-V C H Verlag Gmbh, 2010) Hoehn, Peter; N/A; Department of Chemistry; Afyon, Semih; Somer, Mehmet Suat; Master Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178882The transparent dark orange compounds Cs-2[Pd(N-3)(4)] and Rb-2[Pd(N-3)(4)]center dot 2/3H(2)O are synthesized by reaction of the respective binary alkali metal azides with K2PdCl4 in aqueous solutions. According to single-crystal X-ray diffraction investigations, the novel ternary azidopalladates(II) crystallize in the monoclinic space group P2(1)/c (no. 14) with a = 705.7(2) pm, b = 717.3(2) pm, c = 1125.2(5) pm, beta = 104.58(2)degrees, mP30 for Cs2[Pd(N-3)(4)] and a = 1041.4(1) pm, b 1292.9(2) pm, c = 1198.7(1) pm, beta = 91.93(1)degrees, MP102 for Rb-2[Pd(N-3)(4)]center dot 2/3H(2)O, respectively. Predominant structural features of both compounds are discrete [Pd-II(N-3)(4)](2-) anions with palladium in a planar coordination by nitrogen, but differing in point group symmetries. The vibrational spectra of the compounds are analyzed based on the idealized point group C-4h of the spectroscopically relevant unit, [Pd(N-3)(4)](2-) taking into account the site symmetry splitting due to the symmetry reduction in the solid phase.