Aktaş, İbrahim

Accurate precursor calculation is essential for the successful synthesis of oxide-based superconductors. This study compares two commonly used methods stoichiometric balance and conversion factor (CF) approaches in the synthesis of YBa2Cu3O7-δ (Y123) and Y3Ba5Cu8O18+δ (Y358) superconductors. The analysis reveals that CF methods introduce substantial systematic errors, particularly for Y2O3, with deviations reaching 21.2% in Y123. These errors are exacerbated in Y358 due to its increased stoichiometric complexity. Unlike stoichiometric methods, CF approaches neglect volatile losses such as CO2 and fail to adjust for oxygen non-stoichiometry (δ variations), leading to misestimations in precursor masses. Statistical tests (χ2 < 0.001, RMSE) and experimental data confirm that these inaccuracies can negatively impact phase purity and crystallographic quality. A strong correlation (R2 = 0.847) between stoichiometric accuracy and phase formation quality emphasizes the importance of rigorous calculation. This study highlights the inherent limitations of CF-based shortcuts and underscores the necessity of comprehensive stoichiometric modeling, especially in complex oxide systems. The findings also provide an educational framework to address common misconceptions in materials synthesis, particularly for early-stage researchers in solid-state chemistry and materials science.

Aktaş, İbrahim; Aktaş, Meltem; Cumhur, Ishak

In this study, YBCO (358) superconductor have been investigated by means of magnetic moment-temperature measurements and theoretical analysis. Magnetic moment-temperature curves were evaluated for dependence of oxygen ratio during sintering. From the examinations of the experimental results of the samples, change of oxygen ratio was seen to change the pattern of moment-temperature curves. Experimental results are qualitatively discussed in the framework of the critical state model. The variation of the critical current density values from 50 to 100 and zero, caused the change in oxygen ratio from zero percent to 50% and 100 %, respectively. The field and temperature dependence of the critical current density for each sample were determined from the theoretical and experimental best fit curves. Best fit curves were obtained for M-T data and the used parametric values were compared for each sample. It was seen that the results were consistent with the literature.

Aktaş, İbrahim; Baricz, Árpád; Singh, Sanjeev

Some geometric properties of a normalized hyper-Bessel functions are investigated. Especially we focus on the radii of starlikeness, convexity, and uniform convexity of hyper-Bessel functions and we show that the obtained radii satisfy some transcendental equations. In addition, we give some bounds for the first positive zero of normalized hyper-Bessel functions, Redheffer-type inequalities, and bounds for this function. In this study we take advantage of Euler–Rayleigh inequalities and Laguerre–Pólya class of real entire functions, intensively.

Aktaş, İbrahim

Bu makalenin temel amacı normalize edilmiş hata fonksiyonunun kısmi toplamlarına oranının reel kısımları için bazı alt sınırlar belirlemektir. Ek olarak, normalize edilmiş hata fonksiyonu ve türevinin mutlak değerleri için bazı üst sınırlar da verilmiştir.

Aktaş, İbrahim; Baricz, Árpád

In this paper the radii of starlikeness of Jackson’s second and third q-Bessel functions are considered and for each of them three different normalization are applied. By applying Euler–Rayleigh inequalities for the first positive zeros of these functions tight lower and upper bounds for the radii of starlikeness of these functions are obtained. The Laguerre–Pólya class of real entire functions plays an important role in this study. In particular, we obtain some new bounds for the first positive zero of the derivative of the classical Bessel function of the first kind.