Unusual butterfly-shaped magnetization signals and spin-glass-like behaviour in highly oriented pyrolytic graphite

We report a novel investigation on the relationship between magnetic-ordering and graphitic-structure in highly-oriented-pyrolytic-graphite (HOPG). By employing orientation-dependent-X-ray-diffraction, Raman-spectroscopy and temperature-dependent-superconductive-quantum-interference-device (T-SQUID) we examined the presence of ferromagnetic- and superconductive-ordering in HOPG systems with 1) disordered (HOPG1, containing carbon-vacancy-rich weak-Bernal-stacking and Moiré-superlattices with θmisfit ∼ 0.5°) and 2) ordered (HOPG2, containing higher-degree of Bernal-stacking and Moiré-superlattices with θmisfit ∼ 0.5°, 0.8°, 11°) graphitic-layer-arrangement. A perfect-HOPG is expected to exhibit a diamagnetic-response to an applied-magnetic-field. Instead, additional 1) ferromagnetic-signals presenting a characteristic width-enhancement with the field increasing in HOPG1 and 2) complex butterfly-shaped ferromagnetic signals in HOPG2, are demonstrated. Temperature-dependent-magnetometry evidenced further the presence of randomly oriented ferromagnetic clusters originating from topological disorder in both HOPG1 and HOPG2. These magnetic signals were explained on the basis of the percolative-type model

Inovatyviųjų funkcinių medžiagų agregatų, konformacinių ir dinaminių vyksmų virpesinė spektrometrija

Materials which have particular physico-chemical properties and a unique structure which allows them to be used for a specific function are called functional materials. The development of technology and the application of these materials aims to preserve their valuable properties and structures under different environmental conditions. Many different methods are used to study such materials, providing information on the structure of the materials, possible interactions with impurities, and phase transitions. Hydrogen bonding is one of the main interactions determining the formation, conformational and dynamic processes of ionic liquids, calcium hydroxyapatites and aqueous mixtures thereof. Vibrational spectroscopy techniques are particularly sensitive to structural changes due to the formation or destruction of hydrogen bonding. The dissertation deals with the change of spectral parameters during structural changes and phase changes in functional materials and their aqueous mixtures. Changes in Raman spectral parameters have been found to identify the liquid crystalline ionogel phases and \"water pockets\" formed in ionic liquid-water mixtures. Structural differences of hydroxyl groups in nanostructured calcium hydroxyapatites synthesized by sol-gel method using different complexing agents were investigated for the first time by vibrational spectroscop

Effect of cation-anion interactions on the structural and vibrational properties of 1-buthyl-3-methyl imidazolium nitrate ionic liquid

The cation-anion interactions present in the 1-butyl-3-methylimidazolium nitrate ionic liquid [BMIm][NO3] were studied by using density functional theory (DFT) calculations and the experimental FT-Raman spectrum in liquid phase and its available FT-IR spectrum. For the three most stable conformers found in the potential energy surface and their 1-butyl-3-methylimidazolium [BMIm] cation, the atomic charges, molecular electrostatic potentials, stabilization energies, bond orders and topological properties were computed by using NBO and AIM calculations and the hybrid B3LYP level of theory with the 6-31G* and 6-311++G** basis sets. The force fields, force constants and complete vibrational assignments were also reported for those species by using their internal coordinates and the scaled quantum mechanical force field (SQMFF) approach. The dimeric species of [BMIm][NO3] were also considered because their presence could probably explain the most intense bands observed at 1344 and 1042 cm−1 in both experimental FT-IR and FT-Raman spectra, respectively. The geometrical parameters suggest monodentate cation-anion coordination while the studies by charges, NBO and AIM calculations support bidentate coordinations between those two species. Additionally several quantum chemical descriptors were also calculated in order to interpret various molecular properties such as electronic structure, reactivity of those species and predict their gas phase behaviours.Fil: Kausteklis, Jonas. Vilnius University; LituaniaFil: Aleksa, Valdemaras. Vilnius University; LituaniaFil: Iramain, Maximiliano Alberto. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Brandan, Silvia Antonia. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Inorgánica; Argentin

DFT and vibrational spectroscopy study of 1-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid

Structural and vibrational characterizations for the 1-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid ([BMIM][OTF]) were performed combining the experimental Raman spectrum with density functional theory (DFT) calculations based in the hybrid B3LYP/6-311++G** level of theory. Structurally, the trifluoromethanesulfonate anion, [OTF] is linked to 1-butyl-3-methylimidazolium cation, [BMIM] by a bidentate coordination by means of two different S?O??H hydrogen bonds. The [OTF] anion plays a very important role in the structure and stability of [BMIM][OTF], as observed by the strong increase in the dipole moment value when the anion is added to cation. Intramolecular H and halogen bonds evidence the high stability of ionic liquid, as supported by NBO and AIM calculations. Very good correlations were observed between the predicted infrared and Raman spectra with the corresponding experimental ones. The different Mulliken charges observed on the O atoms of O??H bonds support the asymmetric bidentate coordination of [OTF] anion with the [BMIM] cation. The [OTF] anion increase the reactivity of [BMIM][OTF], as compared with [BMIM][NO3]. In addition, the [OTF] anion reduces drastically the electrophilicity and nucleophilicity indexes of cation evidencing the strong influence of anion on the properties of cation. The vibrational analyses have revealed a very important shifting of one of the two antisymmetric modes of [BMIM][OTF] towards lower wavenumbers due probably to an asymmetric of S[dbnd]O⋯H bond interaction which is no observed in the anion. The complete vibrational assignments were performed for ionic liquid, cation and anion and the harmonic scaled force constants were reported at the same level of theory.Fil: Kausteklis, Jonas. Vilniaus Universitetas;Fil: Aleksa, Valdemaras. Vilniaus Universitetas;Fil: Iramain, Maximiliano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; ArgentinaFil: Brandan, Silvia Antonia. Universidad Nacional de Tucumán; Argentin