Browsing by Author "Mitrić, M"

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    Fluorine doping of layered NaxCoO2 structure
    (Materials Research Society of Serbia, 2015-09-04) Jugović, D; Milović, M; Mitrić, M; Cvjetićanin, N; Avdeev, M; Jokić, BM; Uskoković, D
    The room temperature Na-ion secondary battery has been under focus lately due to its feasibility to compete against the already well-established Li-ion secondary battery. Transition metal oxides of general formula NaxMO2 have been investigated as potential cathode materials for sodium batteries. Layered NaxCoO2 is synthesized via solid-state method at 900 ºC in air atmosphere. Fluorine doping of the as-prepared powder is established by the use of ammonium hydrogen difluoride (NH4HF2) as a fluorinating agent. The fluorination takes place only at low temperature (200 ºC), while the treatment at higher temperatures (≥ 400 ºC) facilitates the formation of NaF. It is shown that various and controllable amounts of fluorine can be successfully incorporated into the structure. Finally, the effects of fluorine doping on both structural and electrochemical properties are examined.
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    Li2FeSiO4 cathode material: the structure and electrochemical performances
    (Materials Research Society of Serbia, 2014-09-01) Jugović, D; Milović, M; Mitrić, M; Ivanovski, VN; Avdeev, M; Jokić, B; Dominko, R; Uskoković, D
    Monoclinic Li2FeSiO4 that crystallizes in P21/n space group was investigated as a potential cathode material for lithium-ion batteries. A combined X-ray diffraction and Mössbauer spectroscopy study was used for the structural investigation. It was found that the crystal structure is prone to an “antisite” defect, the one in which the Fe ion and the Li ion exchange places. This finding was also confirmed by the Mössbauer spectroscopy. In order to obtain composites of Li2FeSiO4 and carbon, several synthesis techniques that use different carbon sources were involved. Electrochemical performances were investigated through galvanostatic charge/discharge tests. Discharge curve profile did not reflect a two-phase intercalation reaction (no obvious voltage plateau) due to the low conductivity at room temperature. © 2014 Materials Research Society of Serbia
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    New insights into BaTi1–xSnxO3 (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data
    (International Union of Crystallography, 2016-01-01) Veselinović, L; Mitrić, M; Avdeev, M; Marković, S; Uskoković, D
    Neutron powder diffraction (NPD) was employed to further investigate the BaTi1−xSnxO3 (BTS) system previously studied by X-ray diffraction. The room-temperature phase compositions and crystal structures of BTS samples with x = 0, 0.025, 0.05, 0.07, 0.10, 0.12, 0.15 and 0.20 were refined by the Rietveld method using NPD data. It is well known that barium titanate powder (x = 0) crystallizes in the tetragonal P4mm space group. The crystal structures of the samples with 0.025 ≤ x ≤ 0.07 were refined as mixtures of P4mm and Amm2 phases; those with x = 0.1 and 0.12 show the coexistence of rhombohedral R3m and cubic phases, while the samples with x = 0.15 and 0.20 crystallize in a single cubic Pm{\overline 3}m phase. Temperature-dependent NPD was used to characterize the BaTi0.95Sn0.05O3 sample at 273, 333 and 373 K, and it was found to form single-phase Amm2, P4mm and Pm{\overline 3}m structures at these respective temperatures. The NPD results are in agreement with data obtained by differential scanning calorimetry and dielectric permittivity measurements, which show a paraelectric–ferroelectric transition (associated with structural transition) from Pm{\overline 3}m to P4mm at about 353 K followed by a P4mm to Amm2 phase transition at about 303 K. © International Union of Crystallography