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    The structural studies and optical characteristics of phase-segregated Ir-doped LuFeO3-? films
    (Springer Heidelberg, 2023) Polat, O.; Coskun, F. M.; Yildirim, Y.; Sobola, D.; Ercelik, M.; Arikan, M.; Coskun, M.
    In this work, we carefully examined how Ir substitution into Fe sites can change the band of the LuFeO3 (LFO) material. LFO and Ir-doped LFO (LuFe1-xIrxO3 or LFIO for short, where x = 0.05 and 0.10) thin films were synthesized by utilizing magnetron sputtering techniques. The films were grown on silicon and indium tin oxide (ITO) substrates at 500 degrees C. The crystallographic orientation of the films was examined using X-ray diffraction (XRD) analysis. The crystallographic orientation of the thin films was examined using an X-ray diffractometer (XRD). For surface topography research, atomic force microscopy (AFM) was employed. To look for the recombination of photogenerated electron-hole pairs in the materials under investigation, photoluminescence (PL) spectroscopy was used. Raman spectroscopy is then utilized to gather data on crystal symmetry as well as disorders and defects in the oxide materials. It was demonstrated that the LFO band gap was altered from 2.35 to 2.72 eV by Ir substitution into Fe sites. Moreover, diffuse reflectance spectroscopy (DRS) was used to analyze conductivity, real and imaginary components of the dielectric constant, refractive index (n), extinction coefficient (k), and reflectance percentage.
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    The electrical and dielectric features of Al/YbFeO3/p-Si/Al and Al/YbFe0.90Co0.10O3/p-Si/Al structures with interfacial perovskite-oxide layer depending on bias voltage and frequency
    (Springer, 2024) Coskun, M.; Polat, O.; Orak, I.; Coskun, F. M.; Yildirim, Y.; Sobola, D.; Turut, A.
    In this investigation, thin films of YbFeO3, both in its pure form and doped with 10% Co, were fabricated on a p-Si substrate at 500 degrees C through the radio-frequency magnetron sputtering method. Examination via Scanning Electron Microscopy demonstrated a porous texture for the pure sample, contrasting with a smooth and crack-free surface post-Co doping. Analysis via X-ray photoelectron spectroscopy unveiled Yb's 3 + oxidation state, alongside the presence of lattice oxygen, oxygen vacancies, and adsorbed oxygen evident in Gaussian fitting curves. Photoluminescence spectroscopy revealed an augmented emission intensity, likely attributed to increased defect initiation in the Co-doped specimen. Moreover, Raman spectroscopy was employed to identify vibration modes in the examined samples, demonstrating shifts in Raman peaks indicative of Co substitution and subsequent distortion in the crystal structure of YbFeO3. Electrical assessments were conducted at room temperature (300 K) under ambient conditions, employing voltage and frequency as variables. Capacitance-voltage measurements illustrated the emergence of an accumulation, with depletion and inversion regions manifesting at different frequencies based on the applied voltage, attributed to the YbFeO3 interfacial layer at the Al and p-Si interface. The conductance-voltage characteristics indicated that the structure exhibited maximum conductance in the accumulation region. Series resistance for these configurations was deduced from capacitance-conductance-voltage measurements, indicating a dependence on both bias voltage and frequency. The doping process led to a reduction in capacitance and series resistance, accompanied by an increase in conductance values. After obtaining corrected capacitance and conductance parameters, it became evident that series resistance significantly influences both parameters. Interface state density (N-ss), determined through the Hill-Coleman relation demonstrated a decreasing trend with increasing frequency. The pure sample exhibited higher interface state density compared to the Co-doped sample at each frequency, highlighting that the 10% Co-doped YbFeO3 thin film enhances the quality of the metal-semiconductor interface properties compared to the pure contact.
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    Variation in the dielectric and magnetic characteristics of multiferroic LuFeO3 as a result of cobalt substitution at Fe sites
    (Elsevier Science Sa, 2023) Polat, O.; Coskun, M.; Yildirim, Y.; Roupcova, P.; Sobola, D.; Sen, C.; Durmus, Z.
    Due to its electrical, magnetic, and optical characteristics, LuFeO3 (LFO) has caught the scientific community's interest. In this study, the powders of LFO, LuFe0.95Co0.05O3, and LuFe0.90Co0.10O3 samples were prepared by using the well-known solid-state approach. The crystalline structure of the fabricated samples was examined by an X-ray diffractometer (XRD). It was found that the samples display secondary phases such as Lu2O3, Lutetium Tetraoxodiferrate, and Wustite. It was shown by scanning electron microscope (SEM) that particle size decreases with Co doping. X-ray photoelectron spectroscopy (XPS) determined oxidation states for Fe and Co. It was presented that Fe has a mixture of 2 + and + 3 valance states in the LFO sample. Although LuFe0.95Co0.05O3 has only the 3 + state, LuFe0.90Co0.10O3 sample has coexisting metallic and 3 + states. The conductivity and dielectric constant of the undoped LFO sample were higher than those of Co doped LFO samples. A decrease in both the dielectric constant and conductivity was associated with a lack of Fe2+ ions and lattice distortions. Furthermore, it was argued that several conduction models must be developed to explain the conduction process in the analyzed samples. Magnetic experiments using a vibrating sample magnetometer (VSM) revealed that Co doping raises Mr values. We discuss that this increase in Mr values could be related to i) variations in the inclined angles of Fe3+ moments and ii) the growth of magnetocrystalline anisotropy's energy.