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(NiO) x (Bi 1.6 Pb 0.4 )Sr 2 Ca 2 Cu 3 O 10-δ composite, where 0.0 ≤ x ≤ 0.2 wt%., were prepared using solid state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). Vickers microhardness measurements (H V ) were carried out at room temperature under different applied loads varying from 0.49 to 9.8 N, and dwell times (40 and 59 s). It was noted that dwell time and Vickers microhardness were inversely proportional. H V values increase as x increases up to 0.1 wt%, and then they decrease with further increases in x. All samples exhibit indentation size effect (ISE) with normal trend, as Vickers microhardness decreases by increasing the applied loads. Also, Vickers microhardness measurements of the prepared samples were done during both loading forces up to 9.8 N and unloading downwards to 0.49 N. It was noted that unloading values of Vickers microhardness are slightly greater than loading values. The elastic/plastic deformation model (EPD) was used to interpret the loading and unloading Vickers microhardness results. It is clearly noted that values of d o, the added elastic component the measured plastic indentation semi-diagonal (d),in the unloading results are much higher than those for loading data. The effect of liquid nitrogen immersion for 16 h on Vickers microhardness values was examined. A significant improvement in the Vickers microhardness of (Bi, Pb)-2223 samples immersed in liquid nitrogen was observed. Such behavior is attributed to the fact that nitrogen immersion increases the volume contraction of the superconductor matrix, causing the shrink of the pores and voids present in the samples. Different models were used to analyze the obtained results such as Meyer's law, Hays–Kendall (HK) approach, elastic/plastic deformation (EPD) model, and modified proportional specimen resistance (MPSR) model. The experimental results of Vickers microhardness of both samples without and with liquid nitrogen immersion are well fitted according to the MPSR model. [ABSTRACT FROM AUTHOR]

Highlights: [•] The effect of nanosized ZnFe2O4 on the Gd-123 phase was studied. [•] The phase formation and superconducting parameters were improved up to x =0.06wt.%. [•] The Vickers microhardness number increased as x increased. [•] The Vickers microhardness data agreed with the proportional specimen resistance model. [ABSTRACT FROM AUTHOR]

CuTlBaCaPrCuO superconducting samples, with 0≤ x≤0.15, were prepared by a single-step solid state reaction on a form of rectangular bar. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The room temperature Vickers microhardness was measured at different loads (0.25-3 N). The experimental results were analyzed using Meyer's law, Hays-Kendall approach, elastic/plastic deformation model, proportional specimen resistance model, and the indentation-induced cracking (IIC) model. Surprising results were obtained and showed that all samples in the form of rectangular bars exhibited reverse indentation size effect in contrary with those in the form of discs. Vickers microhardness values were decreased as Pr-content increased that consisting with the porosity results. Furthermore, the Young's modulus was determined using the dynamic resonance technique. A relation between Young's modulus ( E) and Vickers microhardness ( H) was obtained. [ABSTRACT FROM AUTHOR]

The effect of nano-size MgO (40–60 nm) addition on the physical properties of polycrystalline (Cu0.25Tl0.75)-1234 was studied. The MgO-concentration ( x) varied from 0.0 to 1.0 wt.% of the sample’s total mass. X-ray analysis, granular structure examination, energy dispersive X-ray spectroscopy, electrical resistivity, critical current density at different applied magnetic fields and Vickers microhardness measurements were carried out to study the performance of these samples. Phase examination by X-ray diffraction indicated that MgO-addition enhanced the (Cu0.25Tl0.75)-1234 phase formation till x=0.6 wt.%. Granular investigation by scanning electron microscope reveled that both number and size of voids decreased as x increased from 0.0 to 0.6 wt.%. These results were supported by the sample’s porosity calculation. The superconducting transition temperature and critical current density were found to have optimum values at x=0.6 wt.%. Furthermore, the Vickers microhardness increased till x=0.6 after that it decreased with further increase in x. [ABSTRACT FROM AUTHOR]

The current study investigated the effect of adding yttrium iron garnet (Y 3 Fe 5 O 12 ; YIG) nanoparticles to the (Bi 1.8 Pb 0.4)Sr 2 Ca 2.1 Cu 3.2 O y ((Bi,Pb)-2223) superconductor. The classical solid-state reaction technique was used to synthesize the nano-(YIG) x /(Bi,Pb)-2223 composites (0.00 ≤ x ≤ 2.00 wt.%). X-ray diffraction (XRD) confirmed the formation of tetragonal (Bi,Pb)-2223 as the major phase. The morphology and elemental composition of the synthesized samples were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. Iodometric titration analysis proved that the addition of nano-YIG increased the oxygen content in the CuO 2 planes. The critical transition temperature (T c) and the critical current density (J c) increased with the nano-YIG addition up to x = 0.25 wt.% with values of 119.25 K and 638.37 A/cm2, respectively. X-ray photoelectron spectroscopy (XPS) revealed the elemental composition and oxidation state of all elements in the prepared samples. Room temperature Vickers microhardness (H v) measurements were performed at different applied loads (0.49–9.80 N) and a duration time of 20 s. The best enhancement in Vickers microhardness (H v) was achieved at x = 2.00 wt.%. The modified proportional sample resistance (MPSR) model provided the best theoretical analysis at the plateau limit region based on Vickers microhardness (H v) observations. Moreover, nano-YIG addition into the (Bi,Pb)-2223 superconductor adversely affected several mechanical parameters such as the elastic modulus (E), yield strength (Y), and fracture toughness (K). [ABSTRACT FROM AUTHOR]

Vickers microhardness measurements of Y 3−x Nd x Ba 5−x Ca x Cu 8 O 18−δ samples, 0.00 ≤ x ≤ 0.40, were carried out at room temperature at different applied loads varies from 0.25 N to 10.00 N. Vickers microhardness decreases as the substitution content increases, as well as it decreases as the applied loads increase. The results were analyzed using different models such as Meyer's law, Hays–Kendall (HK) approach, elastic/plastic deformation (EPD) model, proportional specimen resistance (PSR) model and modified proportional specimen resistance (MPSR) model. The analysis shows that the MPSR model is the most suitable one to describe the load independent microhardness for Y 3−x Nd x Ba 5−x Ca x Cu 8 O 18−δ superconducting samples at high load. Some important mechanical parameters such as Young's modulus ( E ), yield strength ( Y ), fracture toughness ( K f ) and brittleness index ( B i ) were calculated as a function of substitution content. The results show that they decrease by increasing the substation content for Y 3−x Nd x Ba 5−x Ca x Cu 8 O 18−δ samples. [ABSTRACT FROM AUTHOR]

Superconducting samples of type (CuTl)-1223 added with nano-FeO ( x=0.0, 0.1, 0.2, 0.4, 0.6 and 1.0 wt.%) were prepared by solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE), whereas the Oxygen-content of these samples was obtained using non Rutherford backscattering spectroscopy at 3 MeV proton beam. It was found that the Oxygen-content of (CuTl)-1223 phase was not affected with the addition of nano-FeO. The electrical resistivity measurements showed that the superconducting transition temperature ( T) increases up to x=0.2 wt.%, followed by a systematic decrease for x>0.2 wt.%. In addition, room temperature Vickers microhardness ( H) measurements were carried out at different applied loads (0.49-2.94 N) to study the performance of the mechanical properties of samples. The experimental results of H were analyzed using different models such as elastic, energy dissipation, energy balance and modified energy balance models. It has been found that the energy dissipation model is in a good agreement with the microhardness data. [ABSTRACT FROM AUTHOR]

The effect of nanosized particles NiO addition on the Vickers microhardness of polycrystalline SmBa2Cu3O7-δ was investigated. Various amounts of nanosized particles NiO (x = 0.00, 0.02, 0.04, 0.08, and 0.12 wt%) were added to SmBa2Cu3O7-δ prepared by the solid-state reaction method. Sample characterizations were carried out using X-ray powder diffraction (XRD), particle induced X-ray emission (PIXE), Rutherford backscattering (RBS), and scanning electron microscopy (SEM). The nanosized particle addition does not influence the orthorhombic structure of SmBa2Cu3O7-δ, whereas it affects the oxygen content δ. The electrical and mechanical properties of (NiO)xSmBa2Cu3O7-δ samples were measured using four-standard probe technique and Vickers microhardness in order to investigate the effect of NiO nanosized particles on superconducting transition temperature and Vickers microhardness number Hv. The Vickers microhardness data were analyzed using Hays and Kendall (HK), elastic plastic deformation (EPD), and modified proportional specimen resistance (MPSR) models. The analysis showed that the MPSR model was found to be the best to describe the behavior of Hv. [ABSTRACT FROM AUTHOR]

The influence of single wall carbon nanotubes SWCNTs and multi wall carbon nanotubes MWCNTs on Vickers microhardness of Gd-123 superconducting phase is studied. Samples of type (SWCNTs) x and (MWCNTs) x GdBa 2 Cu 3 O 7−δ , composite where, 0.0 ≤ x ≤ 0.1 wt.%, are prepared by solid-state reaction technique. The samples are characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM). Moreover the samples are examined by measuring electrical resistivity and Vickers microhardness. The obtained results showed an enhancement in the phase formation and grains connectivity up to 0.06 and 0.08 wt.% for SWCNTs and MWCNTs added samples, respectively. Likewise the superconducting transition temperature T c was improved at a low content of CNTs but it suppressed for higher concentrations. In addition, the analysis of Vickers microhardness measurements suggests that the most suitable model that describes the behavior of our sample is proportional specimen resistance PSR model. [ABSTRACT FROM AUTHOR]