Profile Picture

Email Address

Birth Date

Research Projects

Organizational Units

Job Title

Dr. Öğr. Üyesi

Last Name


First Name



Search Results

Now showing 1 - 7 of 7
  • Publication
    Os doped YMnO3 multiferroic: A study investigating the electrical properties through tuning the doping level
    (Elsevier Science Sa, Po Box 564, 1001 Lausanne, Switzerland, 2018-07-05) Coşkun, Merve; Durmuş, Zehra; Çağlar, Müjdat; Turut, Abdulmecit; POLAT, ÖZGÜR; 110485; 21994; 3726
    Previously, it has been demonstrated the electrical and magnetic properties of YMnO3 (YMO) can be tuned with substitution of different elements into Y and/or Mn sites. In this study, the electrical properties of YMO were explored via substituting osmium (Os) into Mn site with various mol %. The crystalline morphology of synthesized YMnO3 and YMn1-xOsxO3 (YMOO) (x = 0.01, 0.05, 0.10) powders were characterized with X-ray diffractometer (XRD) and infrared spectroscopy (IR) measurements. The crystalline morphology of synthesized powders was studied via scanning electron microscope (SEM). Oxidation states of constituent elements have been examined by X-ray photoelectron spectroscopy (XPS). Electrical properties of YMO and YMOO powders were investigated by dielectric/impedance spectrometer at various temperatures and frequencies. Electric modulus measurements unveiled that for each of x = 0, 0.01 and 0.05 samples there are three relaxation peaks while x = 0.10 sample shows four relaxation peaks. It has been shown that dielectric constant and conductivity properties of parent YMO can be enhanced via Os substitution, particularly, 10 mol % Os doped sample has the highest dielectric constant and conductivity at various temperatures and frequency regions. Moreover, the conduction mechanisms were also examined. It turned out that in order to explain conduction mechanism, multiple models need to be considered in the studied materials. (C) 2018 Elsevier B.V. All rights reserved.
  • Publication
    Frequency and temperature dependent electrical and dielectric properties of LaCrO3 and Ir doped LaCrO3 perovskite compounds
    (Elsevier Science Sa, Po Box 564, 1001 Lausanne, Switzerland, 2018-04-05) Coşkun, M.; Coşkun, F. M.; Durmuş, Zehra; Çağlar, Müjdat; Turut, Abdulmecit; POLAT, ÖZGÜR; 110485; 21994; 3726
    Perovskite oxide materials, especially perovskite lanthanum chromium oxide, LaCrO3 (LCO) have taken considerable attention among the scientists due to the changing optical, electrical, dielectric and magnetic properties depending on doping via various elements. In this study, the LCO and iridium (Ir) doped LCO (LaCr1-xIrxO3) (x = 0.10) compounds were synthesized using solid-state reaction method. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) have been employed to study particle morphologies and oxidation states of synthesized powders, respectively. Frequency-depended electrical/dielectric properties of perovskite oxide samples were performed in wide range frequency (1Hz-10 MHz) and temperature (-100 degrees C to +100 degrees C) using dielectric/impedance spectrometer. Electrical measurements have underscored that the dielectric constant of LCO compound dramatically decreased after doped with Ir. Furthermore, it was observed that ac conductivity and capacitance value of LCO decreased while impedance increased after Ir doping due to i) Ir occupation in Cr sites and ii) lattice distortion owing to doping larger ion Ir4+ into smaller Cr3+ ion in the LCO lattice. Finally, overlapping large polaron tunneling (OLPT) and quantum mechanical tunneling (QMT) conduction mechanisms were suggested for LCO while the correlated barrier hopping (CBH) and QMT conduction mechanisms were observed for Ir doped LCO compound. Moreover, the activation energy values have been calculated by employing both f(max) vs. 1/T and sigma(dc) vs. 1/T plots. It has been shown those energy values are in good agreement with each other for LCO and Ir doped LCO samples at various temperature ranges. (C) 2018 Elsevier B.V. All rights reserved.
  • Publication
    Drone ile Teslimat Rotalaması için Bir Matematiksel Model
    (2017) Han, Sinem; Özer, Begüm; Alioğlu, Barış; POLAT, ÖZGÜR; AKTİN, AYŞE TÜLİN; 109203
  • Publication
    Engineering the band gap of LaCrO3 doping with transition metals (Co, Pd, and Ir)
    (Springer, 233 Spring St, New York, Ny 10013 USA, 2018-03) Durmuş, Zehra; Coşkun, Fatih Mehmet; Coşkun, Mustafa; Turut, Abdulmecit; POLAT, ÖZGÜR; 110485; 48508; 33455; 3726
    Exceptional properties such as dielectric, ferroelectric, piezoelectric, magnetic, catalytic, and photovoltaic of perovskite materials open new doors to many groundbreaking discoveries for unique device ideas. These materials properties are inherited from their crystal structures; therefore, the features can be tuned via varying details of the crystal structures. In the literature, LaCrO3 (LCO) is one those mostly examined perovskites for various purposes such as solid oxide fuel cells, catalytic converters, and sensors. In the present study, the band gap tuning of LCO was investigated via doping a transition element such as cobalt (Co), palladium (Pd), and iridium (Ir) into Cr atom. The synthesized doped and un-doped LCO powders were characterized by infrared spectra (IR) and X-ray diffraction (XRD). Scanning electron microscopy (SEM) was employed to study the surface topography of LCO and doped LCO thin films on silicon substrates. The band gaps of the LCO and doped LCO films were scrutinized using a UV-Vis spectrometer. Our study has shown that the band gap of LCO was successfully lowered from 3.4 eV to 2.66 eV and can be engineered via substitution at various mol% of transition elements (Co, Pd, Ir) onto B-site Cr atom in the LCO perovskite structure.
  • PublicationEmbargo
    The electrical modulus and other dielectric properties by the impedance spectroscopy of LaCrO3 and LaCr0.90Ir0.10O3 perovskites
    (Royal Soc Chemistry, Thomas Graham House, Science Park, Milton Rd, Cambridge Cb4 0Wf, Cambs, England, 2018) Coşkun, Merve; Coşkun, Fatih Mehmet; Durmuş, Zehra; Çağlar, Müjdat; Turut, Abdulmecit; POLAT, ÖZGÜR; 110485; 48508; 108339; 21994; 3726
    We have prepared LaCrO3 (LCO) and 10% Ir doped LCO samples by the solid state reaction method and studied the electrical modulus and the other dielectric properties of the samples by means of the impedance spectroscopy in the -100 degrees C to 100 degrees C range, with steps of 20 degrees C. It has been clearly observed that the dielectric properties change due to Ir doping. The absolute dielectric constant value of Ir doped LCO has decreased and this reduction was attributed to decreasing Cr6+ ions which may play a vital role in space charge polarization and charge hopping. A plateau region appeared in the temperature-dependent real electrical modulus M' versus f curves of the pure LCO sample while almost no plateau region is visible in the Ir doped LCO sample. The temperature-dependent imaginary modulus M" versus f curves has two peaks at each temperature; one of the peaks is at low frequency and the other at the high frequency region, which shifts through higher frequency region with increasing temperature. This originates from free charge accumulation at the interface with the increase of the temperature. Furthermore, it has been seen that the Ir doped LCO sample has higher impedance and resistance values than the undoped LCO sample at the same frequency and temperature. This phenomenon was attributed to doped Ir ions behaving like a donor in LCO because LCO is a p-type compound. Moreover, the activation energy values of 0.224 eV and 0.208 eV for LCO and of 0.161 eV and 0.265 eV for the Ir doped LCO have been obtained from the slopes of the rho(dc) vs. (kT)(-1) curves, respectively. Also the activation energies were calculated from the slopes of the f(ma)x vs. (kT)(-1) curves and the obtained results from low frequency region were in good agreement with rho(dc) vs. (kT)(-1) ones.
  • Publication
    A mathematical model for the delivery routing problem via drones
    (Pamukkale Üniversitesi, 2019) Han, Sinem; Özer, Begüm; Alioğlu, Barış; POLAT, ÖZGÜR; AKTİN, AYŞE TÜLİN
    Logistics sector aims to distribute merchandise to designated places on time, while focusing on the entire process that starts from storing the goods at warehouses. Transportation by land is the most common and preferred way in logistics in terms of cost and service. Studies have been going on for drone transportation with the purpose of reducing the service time and making the process automated. Advancement of this technology has led to an increase in transportation with drones. Traffic is a huge problem in land transportation causing delays in delivery time. Furthermore, nature and economy are affected because of the CO2 emission, which is a consequence of intense traffic. In this study, utilizing drones for delivery is proposed with the aim of increasing customer satisfaction and minimizing transportation cost per delivery in a green way. Istanbul's Bakirkoy district is selected as the implementation region, and daily drug delivery to pharmacies with drones is examined. In the first stage, a mathematical model that uses pharmacy coordinates as an input is developed for clustering analysis. In the second stage, one of these clusters is selected, and the location of the drone center that will serve pharmacies in the cluster is obtained by center of gravity method. Then, a vehicle routing model is proposed for finding the drone routes and calculating the total distance travelled within this cluster. Mathematical models are solved with GAMS/CPLEX solver. It is believed that this study will trigger new studies in "green delivery" literature in near future.
  • Publication
    The characterization of electrical properties of Pd-doped LaCrO3 perovskite structure
    (Springer, Van Godewijckstraat 30, 3311 Gz Dordrecht, Netherlands, 2018-10) Coşkun, Merve; Coşkun, Fatih Mehmet; Durmuş, Zehra; Çağlar, Müjdat; Turut, Abdulmecit; POLAT, ÖZGÜR; 110485; 135337; 48508; 21994; 3726
    In the present study, the electrical properties of LCO were explored via substituting the Pd into Cr sites with various mol%. The crystalline morphology of synthesized LaCrO3 and LaCr1 − xPdxO3 (LCPO) (x = 0.05, 0.10, 0.20) ceramics were characterized via scanning electron microscope (SEM). Oxidation states of constituent elements have been examined by X-ray photoelectron spectroscopy (XPS). Electrical properties of LCO and LCPO ceramics were studied by dielectric/impedance spectrometer at various temperatures, − 100 to 100 °C, and a wide frequency range (1–107 Hz). Present work has demonstrated the conductivity and dielectric constant of LCO deteriorate with Pd doping. The calculated power law exponent from ac conductivity reveals that there are different conduction mechanisms in the samples. It has been established the activation energy of the parent LCO rises with increasing the Pd doping. The activation energies from dc conductivity measurements underline that the conduction is owing to polaron hopping based on electron carriers.