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Öğe A-site Pb doping effect on structural, microstructural and magnetotransport properties of La0.5Sm0.2Ca0.3-xPbxMnO3 (x=0, 0.05, 0.10) manganite(Elsevier Science SA, 2021) Denbri, Fatih; Mahamdioua, Nabil; Meriche, Faiza; Koç, Nevin Soylu; Terzioğlu, Cabir; Varilci, Ahmet; Altıntaş, Sevgi PolatStructural, microstructural and magneto-transport properties of polycrystalline La0.5Sm0.2Ca0.3-x PbxMnO3 (x = 0, 0.05 and 0.10) samples, prepared by conventional solid state reaction, were studied. Refinement of the Powder X-ray diffractograms revealed that all the samples crystallize into orthorhombic structure with Pnma space group and the lattice parameters increase with increasing Pb content. The scanning electron microscope (SEM) micrographs show a granular character and the estimated grain sizes ranges between 10 mu m and 20 mu m. The experimental electrical resistivity and the magnetoresistance in the temperature range 20 K-250 K under magnetic field of zero and 1 Ta, have been recorded using four probe technique. The resistivity curves without magnetic field, exhibit a ferromagnetic-metallic (FM) to paramagnetic-insulating (PI) transition at TMI = 125 K, 91 K and 37 K for x = 0, 0.05 and 0.10, respectively. The magnetoresistance reaches 58% for undoped sample and decrease with Pb doping under 1T. The resistivity values increases drastically with Pb doping. These two results were explained mainly by the increase of the disorder sigma 2 and rA TMI) and for x = 0 and 0.05 samples, the resistivity curves is well fitted by a combination of the residual resistivity, weak localization and electron-electron scatterings; in addition to small polaron contribution or electron-phonon interaction respectively. In the high temperature regime T TMI, all our resistivity curves has been analyzed using adiabatic small polaron hopping model (ASPH) above theta D/2 and variable range hopping model (3D-VRH) (TMI < T < theta D/2). An attempt to use the percolation model to describe the resistivity data in the entire temperature range for both x = 0 and 0.05 samples, was established. Finally, density of state, mean hopping distance Rh and mean hopping energy Eh were calculated and discussed.Öğe Enhancing magnetoresistive features of iron-substituted La0.8Sr0.2MnO3 ceramic manganites(Elsevier Sci LTD, 2022) Karadavut, Samed; Denbri, Fatih; Terzioğlu, Cabir; Öztürk, Özberk; Altıntaş, Sevgi PolatThe influence of iron content on the structural, microstructural, magnetic, and electrical-transport features of the ceramic perovskite manganites of the form La0.8Sr0.2Mn1-xFexO3 (x=0.0, 0.05, 0.1, and 0.2) was investigated. A single phase of rhombohedral-distorted structure with an R c space group was confirmed for all synthesized ceramic samples. The microstructures of the manganite ceramics were improved by iron substitution. The magnetic and electrical-transport studies show that samples with x=0.0, 0.05, and 0.1 display phase transitions from ferromagnetic to paramagnetic state and metallic to insulating one with increasing temperature. The phase transition temperatures, i.e., Curie temperature, TC, and the resistance transition temperature TMI, are found to be lowered with the increase in the Fe concentration. The temperature coefficient of resistance (TCR) value for the x=0.0 sample is obtained similar to 2.16% K-1 and slightly decreased to similar to 1.55% K-1 with a 5% Fe substituted sample. As x rise to 0.1, we obtain the maximum TCR value of similar to 8.23% K-1. At the same time, the maximum magnetoresistance is obtained as 48.1% at 233 K for the x=0.1 sample. One of the most important findings in this paper is that Fe substitution is very useful for improving magneto-electrical features of the La0.8Sr0.2MnO3 ceramics. Moreover, to better understand the temperature dependence of the electrical resistivity data, the experimental findings were fitted to the equations of several models.Öğe Investigation of magneto-transport properties of the co-doped La1.6-xPrxCa1.4-xBaxMn2O7 (x=0.2 and 0.4) double-layered manganite(Springer, 2021) Denbri, Fatih; Mahamdioua, Nabil; Meriche, Faiza; Altıntaş, Sevgi Polat; Terzioğlu, CabirStructural and magneto-electrical transport properties of double-layered La1.6-xPrxCa1.4-xBaxMn2O7 (x = 0.2 and 0.4) manganite compounds were studied. X-ray diffraction patterns refinement shows that the samples crystallize in a tetragonal I4/mmm structure, whereas a rhombohedral structure phase with R-3-c space group is detected as a secondary phase. The electrical resistivity under 0 and 1 T exhibited a metal-insulator transition at T-MI. It is found that the rho(T) decreases with increasing Pr-Ba contents. Magnetoresistance (MR%) curves displayed a maximum value of similar to 51.69% at 63 K for the x = 0.2 sample and decreases with increasing Pr-Ba concentrations to similar to 33.44% at 64 K for x = 0.4 under 1 T. The obtained values of the temperature coefficient of resistivity for both samples have similar trend as T-MI. Below T-MI,T- rho(T = rho(0) - rho T-0.5(0.5) + rho T-2(2) + rho T-5(5) model fits well the resistivity curves which reflect a combination of the grain boundary effects, weak localization, electron-electron, and electron-phonon scattering to the electrical resistivity. Above T-MI, the non-adiabatic small polaron hopping model describes the electrical resistivity behavior in T > theta(D)/2 region. The Mott's 3D variable range hopping mechanism (3D-VRH) was found to be the most suitable mechanism for describing the high-temperature resistivity behavior between T-MI and theta(D)/2. The density of states near the Fermi level N(E-F) and mean hopping energy (E-h) of the charge carriers have been calculated from the experimental curves using Mott's 3D-VRH model. The experimental and fitting curves of the resistivity and the related results are discussed in detail.Öğe Non-adiabatic small-polaron and 3D-Mott's variable range conductions above 100 K in Pb-substituted double-layered manganites LaSm0.4Ca1.6-xPbxMn2O7(Pergamon-Elsevier Science Ltd, 2022) Denbri, Fatih; Mahamdioua, Nabil; Meriche, Faiza; Altıntaş, Sevgi Polat; Terzioğlu, CabirIn this study, the role of Pb substitution on the microstructural and magneto-transport properties of the double layered manganites LaSm0.4Ca1.6-xPbxMn2O7 (x = 0, 0.1 and 0.2), prepared by the solid-state reaction method, was investigated. On the samples, X-Ray Diffraction, Scanning Electron Microscopy and resistivity as a function of temperature measurements were performed. XRD measurements revealed that the samples crystallized in a tetragonal phase with an I4/mmm space group and that the lattice parameters increased with increasing Pb content. SEM measurements indicated the granular character and the average grain sizes ranged between 0.5 and 4 mu m for all the samples. The temperature dependence of resistivity of all the samples shows insulating-like behavior for the studied range of temperature (T > 100 K). The maximum magnetoresistance (MR%) value was found to be 31.95% at 100 K for the sample with x = 0, while it was 11% and 8% for the samples with x = 0.1 and 0.2, respectively. The resistivity curves are found to be well described by the Adiabatic Small Polaron Model in the range and Mott's 3D Variable Range Hopping model in the range. The density of states near the Fermi level (DOS), mean hopping distance, and mean hopping energy values were computed in the range, and the role of Pb substitution on these parameters was discussed as well.Öğe Structural, electrical, magnetic and magnetotransport properties of La0.7Ca0.18Ba0.12Mn0.95Sn0.05O3 manganite prepared with different quenching processes(Springer Heidelberg, 2023) Belal, Ibtihal; Meriche, Faiza; Mahamdioua, Nabil; Denbri, Fatih; Altıntaş, Sevgi Polat; Terzioğlu, CabirStructural, microstructural, magnetic, electrical and magneto-transport properties of La0.7Ca0.18Ba0.12Mn0.95Sn0.05O3 manganite powders, prepared by the solid state method, were investigated. Two quenching processes were performed on the samples: quenching in air and quenching to 77 K in liquid nitrogen. X-ray diffraction patterns refinement revealed that the samples crystallized in the orthorhombic structure. The scanning electron microscopy micrographs presented granular characters. The magnetization vs temperature plot showed a paramagnetic-ferromagnetic transition. The inverse susceptibility chi(-1)(T) deviation from the Curie-Weiss law revealed the existence of the phase above T-C in the nitrogen-quenched sample. The hysteresis cycles reveal that the samples are ferromagnetic at 1.8 K and paramagnetic at 300 K. The resistivity curves exhibit a ferromagnetic-metallic to paramagnetic-insulating transition. The magnetoresistance increased slightly in the sample quenched to 77 K in N-2.Öğe Synthesis and experimental study of structure, magnetotransport properties and temperature coefficient of resistance of La0.7Ca0.18Ba0.12Mn0.95Sn0.05O3 manganite(Springer/Plenum Publishers, 2022) Boufigha, S.; Mahamdioua, Nabil; Denbri, Fatih; Altıntaş, Sevgi Polat; Terzioğlu, CabirLa0.7Ca0.18Ba0.12Mn0.95Sn0.05O3 compound has been successfully prepared by the solid-state reaction route. The structural, electrical, magnetotransport properties, as well as the temperature coefficient of resistance, were experimentally characterized and discussed. Rietveld's refinement of the X-ray diffractogram revealed that the compound crystallizes in an orthorhombic structure with a Pnma space group. The estimated crystallite size is about 43 nm. The SEM micrographs revealed the granular nature and polygonal grain shape of the sample. The electrical resistivity curves, carried out between 20 and 300 K, show a metal-to-insulator transition and an upturn at a very low-temperature range (20 K < T< 32 K). The magnetoresistance maximum value reached 23.23% at 20 K under 1 Tesla. The temperature coefficient of resistance curves exhibits a slight characteristic peak around TMI, and its value is around 1.96%. Fitting the electrical resistivity curves in the metallic region (32 K < T <= T-MI) confirms that the resistivity behavior is governed by a combination of residual resistivity, electron-electron scattering process, and electron-phonon interaction, whereas in the insulating region (T >= theta(D)/2), it is governed by adiabatical small polarons hopping.
