Özkul, İskender; Kalay, Ece; Güler, Seval Hale; Karaduman, Oktay; Şimşek, Telem; Bülbül, Zeynel Abidin; Aksu Canbay, Canan; Sen Baykal, Duygu; ALMisned, Ghada; Tekin, H.O.

Rare-earth substitution provides a route for tailoring the structural, magnetic, and gamma-ray attenuation behaviour of Ho-based Co-Mn double perovskites; however, the combined effects of rare-earth ionic size, magnetic character, and substitution level remain insufficiently understood. In this study, Ho1.5La0.5CoMnO6, Ho1.2Er0.8CoMnO6, Ho1.3Sm0.7CoMnO6, and Ho2CoMnO6 were synthesized through a two-step route involving mechanical alloying to obtain precursor powders, followed by annealing at 1000 °C in air to promote oxidation and double-perovskite phase formation. Their structural, thermal, surface-chemical, magnetic, and gamma-ray attenuation properties were examined by X-ray diffraction, thermal analysis, X-ray photoelectron spectroscopy, SEM-EDS, vibrating-sample magnetometry, and theoretical shielding calculations based on half-value layer (HVL) and transmission factor (TF) parameters. The XRD patterns were consistent with predominantly monoclinic P21/n type double-perovskite structures, while weak additional reflections suggested possible minor secondary phases. SEM-EDS showed homogeneous elemental distributions, and XPS analysis indicated Co2+ dominated and mixed Mn-valence characteristics in the spectra where reliable component analysis was possible. All compositions exhibited a low-temperature ferromagnetic-like field response but did not reach magnetic saturation at 3 T. Ho2CoMnO6 and Ho1.3Sm0.7CoMnO6 showed the highest field-dependent magnetization values at 10 K, whereas Ho1.2Er0.8CoMnO6 displayed the lowest response. The theoretical gamma-ray attenuation calculations showed clear composition-dependent differences. At 0.662 MeV, the HVL values were 1.0650, 0.9972, 1.0438, and 0.9967 cm for Ho1.5La0.5CoMnO6, Ho1.2Er0.8CoMnO6, Ho1.3Sm0.7CoMnO6, and Ho2CoMnO6, respectively. At the same photon energy and a thickness of 1.0 cm, the corresponding TF values were 0.0896, 0.0858, 0.0882, and 0.0860. Thus, Ho1.2Er0.8CoMnO6 and Ho2CoMnO6 exhibited the lowest HVL and TF values among the investigated compositions. The shielding calculations identified Ho1.2Er0.8CoMnO6 and Ho2CoMnO6 as the most effective attenuators, with lower HVL and TF values across the investigated energy range. These results show that rare-earth substitution enables compositional tuning of magnetic and theoretical gamma-ray attenuation behaviour, with the observed trends reflecting the combined influence of rare-earth ionic size, magnetic character, substitution level, and valence-state complexity.

İncele

Özkul, İskender; Güler, Ömer; Kavaz, E.; Kalay, Ece; Güler, Seval Hale; ALMisned, Ghada; Tekin, H.O.

This study investigates three newly designed Ti-Zr-Hf-based high-entropy alloys such as TiZrHfGdSm (N1), TiZrHfEr (N2), and TiZrHfGdEuB (N3), with the aim of understanding how selected rare-earth and boron additions influence microstructural evolution and dual γ-ray/fast-neutron shielding performance. All alloys were synthesized by arc melting and evaluated through thermodynamic modelling, X-ray diffraction, scanning electron microscopy with elemental mapping, and mixed-field attenuation measurements. The results show that each composition forms an HCP-type solid-solution matrix with composition-dependent lattice distortion and secondary phase formation. Among the studied systems, the Er-modified alloy N2 develops the most spatially uniform elemental distribution and demonstrates the most balanced combination of γ-ray attenuation, effective atomic number, buildup behaviour, and fast-neutron removal efficiency. N1 and N3, containing multiple rare-earth elements and, in the case of N3, boron-induced borides, exhibit distinct grain features and provide valuable insights into how multi-element additions shape photon and neutron interaction pathways. Comparative examination confirms that shielding performance in these HEAs is governed by the interplay of elemental cross sections, density, and microstructural uniformity. The findings highlight Ti-Zr-Hf-RE(B) alloys as promising platforms for multifunctional radiation-shielding materials and provide a compositional framework for future optimization in nuclear, medical, and aerospace applications.

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Özkul, İskender; Kalay, Ece; Güler, Ömer; Karaduman, Oktay; Canbay, Canan Aksu; Hameed, Louis Ibrahim; Almisned, Ghada; Baykal, Duygu Sen; Tekin, H.O.

This study investigates the effect of 1 at.% rare-earth (RE = Sm, Gd, Dy) addition on the structural, mechanical, magnetic, and radiation shielding properties of CoFeNiMnTi high-entropy alloys produced by arc melting. X-ray diffraction results reveal an FCC-dominant structure accompanied by secondary Laves-type phases, with increased phase complexity observed in Gd- and Dy-containing alloys. Mechanical evaluation shows a significant hardness enhancement, reaching 581 HV for Gd and 548 HV for Dy, compared to 447 HV for the reference alloy. Magnetic measurements indicate soft-ferromagnetic behaviour for all compositions, with magnetization increasing in the order S0<S1<S2<S3, highlighting the strong influence of Dy on magnetic response. Elemental mapping confirms a homogeneous distribution with minor local compositional variations contributing to phase evolution. Thermodynamic analysis suggests that rare-earth addition increases lattice distortion and chemical complexity without strongly differentiating among RE types. In terms of radiation shielding, linear attenuation coefficients and effective atomic number values demonstrate improved gamma-ray attenuation, particularly at low energies, with Dy exhibiting the highest performance. In contrast, fast neutron removal cross section values remain nearly unchanged, indicating limited sensitivity to dilute RE addition. It can be concluded that the incorporation of Dy results in the most balanced multifunctional performance, whereas Gd primarily enhances mechanical strength, emphasizing the importance of rare-earth selection in the design of high-entropy alloys for radiation-related applications.

İncele

Özkul, İskender; Kalay, Ece; Guler, Omer; Aksu Canbay, Canan

Half-metallic Heusler alloys are promising materials for spintronic and thermoelectric applications. These alloys exhibit metallic conductivity in one spin direction while acting as insulators in the opposite spin direction, enabling nearly 100% spin polarization. This property is crucial for spintronic devices such as magnetic tunnel junctions (MTJs), magnetic random-access memories, and spin-based transistors. This study investigates the electronic, magnetic, and structural properties of Heusler alloys, focusing on their synthesis methods, atomic ordering, and modelling via density functional theory (DFT). DFT-based calculations serve as a key tool for predicting band structures, spin polarization, and magnetic properties. Additionally, the effects of disorder, strain, and compositional changes on material properties are analysed to explore performance optimization strategies. The potential applications of Heusler alloys in spintronic memory devices, thermoelectric energy conversion, and quantum technologies are also discussed. This work is presented as a review article and systematically compiles and interprets findings from the existing literature to provide a broad understanding of the topic. By integrating theoretical and experimental approaches, this study provides a comprehensive overview of the role of these materials in advanced technological applications.

İncele

Karaduman, Oktay; Kalay, Ece; Ozkul, Iskender; Kurgun, Mehmet Ali; Canbay, Canan Aksu; Guler, Omer; ALMisned, Ghada; Baykal, Duygu Sen; Tekin, H.O.

A novel Cu-based high-temperature shape memory alloy (HTSMA) with the composition 70.84Cu–23.80Al–4.14Mn–1.22Fe (at. %) was successfully synthesized via arc melting in this study. The effects of thermal aging duration on the alloy’s martensitic transformation behavior, shape memory effect (SME), and microstructural evolution were systematically investigated. Six samples were prepared from the as-cast ingot: one was homogenized in the β-phase region and quenched into ice-brine to induce a martensitic structure, while five others were subsequently aged at 350 ℃ for varying durations and air-cooled. Thermal and structural characterizations were conducted. These included differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and optical microscopy. Prolonged aging altered transformation temperatures and reduced both enthalpy and entropy values. It also promoted the formation of observed precipitates, vacancies, and coarsened 2H martensites. Prolonged aging altered the microstructure and thermal response, leading to partial SME degradation. Additionally, the alloy’s gamma-ray and fast neutron shielding parameters were theoretically estimated using simulation software to explore its potential functional scope. The calculated results indicate that the CuAlMnFe HTSMA is predicted to exhibit favorable attenuation performance across a wide energy spectrum, with appropriate values of mass attenuation coefficient (MAC) and half-value layer (HVL). In particular, the fast neutron removal cross-section was calculated as 0.139 cm−1, which is significantly higher than those of water (0.1023 cm−1), graphite (0.0773 cm−1), and B4C (0.0714 cm−1). In conclusion, the CuAlMnFe HTSMA developed in this study offers a unique profile combining tailorable shape memory behavior with a computationally predicted potential for nuclear radiation shielding. These properties offer novel insights into the alloy’s potential for applications in high-radiation environments that require both mechanical actuation and radiation protection, pending experimental validation of its shielding performance.

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İncele

Özkul, İskender; Kalay, Ece; Karaduman, Oktay; Kizilgün, Yasİn; Güler, Ömer; Canbay, Canan Aksu

This study investigates the effects of different cerium additions on the properties of Cu-Al-Mn high-temperature shape memory alloy (HTSMA), such as the characteristic martensitic transformation temperatures, transformational kinetic parameters, and martensitic microstructures which are related to its shape memory mechanism and also to its magnetic behavior. Polycrystalline alloys with a base composition of Cu77.32Al21.02Mn1.67 (at.%) were synthesized, and varying concentrations of cerium (Ce-1 to Ce-4) were added for comparison. Differential scanning calorimetry tests revealed notable increments in transformation temperatures with cerium additions. Specifically, the austenite start temperature of the reference alloy increased from 143.75 °C to 194.88 °C by 0.05 at.% of Ce addition (Ce-3 alloy), corresponding to the formation of CeCu5 and Mn1.15Cu3.85Ce phases. However, excessive Ce addition in Ce-4 led to the over-stabilization of secondary phases, reducing the transformation temperatures. Microstructural analysis indicated that Ce addition of refined grains changed the crystallite size of the martensite structure and reduced lattice strain (from 0.72% to 0.34%). Magnetic characterization demonstrated that Ce addition shifted the alloy towards paramagnetic behavior, with M-H curves showing no significant coercive field or remanent magnetization across the studied alloy samples. These findings suggest that cerium can enhance the high-temperature performance of Cu-Al-Mn HTSMAs, with potential applications in environments requiring both shape memory and magnetic properties.

AtıfScopus3·WoS3

İncele

Kalay, Ece; Özkul, İskender; Karaduman, Oktay; Kızılgün, Yasin; Güler, Ömer; Canbay, Canan Aksu; Kilic, G.; Baykal, Duygu Sen; ALMisned, Ghada; Tekin, H.O.

This study systematically investigates the effect of Ce addition on the thermal, structural, and radiation shielding properties of CuAlMn-based high-temperature shape memory alloys (HTSMAs). Among the different compositions, Ce-III demonstrated the most balanced performance, exhibiting optimized phase transformation behavior, microstructural refinement, and enhanced gamma-ray attenuation. Differential Scanning Calorimetry (DSC) analysis revealed that Ce-III exhibited lower transformation temperatures, with austenite start (As) and finish (Af) temperatures of 378.13 °C and 429.75 °C, respectively, and martensite start (Ms) and finish (Mf) temperatures of 402.52 °C and 341.91 °C, suggesting improved thermal stability. Microstructural analysis indicated significant grain refinement, attributed to Ce's dislocation pinning effect, which contributed to enhanced strength and radiation attenuation. X-ray diffraction (XRD) patterns confirmed the formation of Ce-rich intermetallic phases, such as Mn1.15Cu3.85Ce and Cu8Ce4, which increased density and photon interaction probability. The Ce-III alloy exhibited superior linear attenuation coefficients and reduced half-value layer, reinforcing its effectiveness as a radiation shielding material. It can be concluded that Ce-III represents an optimal composition with a synergistic combination of structural stability, phase transformation control, and enhanced radiation shielding capabilities, making it a promising candidate for nuclear and high-radiation applications.

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