Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği

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  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Mn2+ Ions Incorporated Into Znsxse1-X Colloidal Quantum Dots: Controlling Size and Composition of Nanoalloys and Regulating Magnetic Dipolar Interactions
    (IOP Publishing, 2021) Ünlütürk, Seçil Sevim; Akdoğan, Yaşar; Özçelik, Serdar
    A facile synthesis method is introduced how to prepare magnetically active ultraviolet emitting manganese ions incorporated into ZnSxSe1-x colloidal quantum dot (nanoalloy) at 110 degrees C in aqueous solutions. The reaction time is the main factor to control the hydrodynamic size from 3 to 10 nm and the precursor ratio is significant to tune the alloy composition. ZnS shell layer on the ZnSxSe1-x core was grown to passivate environmental effects. The nanoalloy has ultraviolet emission at 380 nm having a lifetime of 80 ns and 7% quantum yield. The incorporation of Mn2+ ions into the nanoalloys induced magnetic activity but did not modify the structure and photophysical properties of the nanoalloys. Colloidal and powdery samples were prepared and analyzed by electron paramagnetic resonance (EPR) spectroscopy. In the colloidal dispersions, EPR spectra showed hyperfine line splitting regardless of the Mn2+ ion fractions, up to 6%, indicating that Mn2+ ions incorporated into the nanoalloys were isolated. EPR signals of the powdery samples were broadened when the fraction of Mn2+ ions was higher than 0.1%. The EPR spectra were simulated to reveal the locations and interactions of Mn2+ ions. The simulations suggest that the Mn2+ ions are located on the nanoalloy surfaces. These findings infer that the magnetic dipolar interactions are regulated by the initial mole ratio of Mn/Zn and the physical state of the nanoalloys adjusted by preparation methods.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 11
    Enhanced Room Temperature Energy Storage Density of Bi(li1/3ti2 Substituted Bi0.5na0.5tio3-Batio3 Ceramics
    (IOP Publishing, 2021) Karakaya, Merve; Adem, Umut
    For high power electronics applications, relaxor ferroelectrics are promising materials due to their superior energy storage properties. In this study, we investigate the energy storage properties of novel lead free relaxor ferroelectric ceramics (1-x)(0.92Bi(0.5)Na(0.5)TiO(3)-0.08BaTiO(3))-xBi(Li1/3Ti2/3)O-3 (abbreviated as BNT-8BT-xBLT). BNT-8BT composition which is close to morphotropic phase boundary was chosen as the base due to its large maximum polarization (P-m) and higher ratio of weakly polar tetragonal phase which is expected to facilitate ergodic relaxor behavior and improve energy storage density. The substitution of BLT to the BNT-8BT strongly disrupts the correlations between the polar nanoregions and the transition from nonergodic to ergodic relaxor state occurs already at x = 0.02 BLT at room temperature. Largest energy density (W-rec) at 61 kV cm(-1) was obtained for x = 0.02 sample (0.656 J cm(-3)), followed by x = 0.03 (W-rec = 0.614 J cm(-3)) and x = 0.05 (W-rec= 0.559 J cm(-3)). The x = 0.02 sample keeps its energy storage density at high temperatures (i.e. W-rec= 0.88 J cm(-3,) eta = 97%, E-m= 65 kV cm(-1) at 125 degrees C), while larger electric field (up to 89 kV cm(-1)) could be applied to the x = 0.05 sample with the smallest grain size and energy density of 1.03 J cm(-3) was reached at room temperature. Energy storage density values of BLT substituted materials normalized per unit applied electric field are promising among BNT-based materials.