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(Mn2O3)x SmBa2Cu3O7-δ composite samples (0.00 ≤ x ≤ 0.08 wt.%) were prepared using solid state reaction technique, and investigated using resistivity measurements and the Vickers microhardness. The characterisation of the prepared samples was accomplished using X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Brunauer-Emmett-Teller (BET). The Mn2O3 nanoparticles do not influence the orthorhombic structure of SmBa2Cu3O7- δ and stay as adhering material producing a filling up of the voids and reducing the cracks. BET measurements show a decrease in the specific surface area as well as in the total pore volume for x = 0.02 wt.%, confirming the SEM results. The superconducting transition temperature Tc of the prepared samples was investigated using electrical resistivity measurements. Results showed that Tc increases from 91.68 K to 94.43 K as x increases from 0.00 to 0.02 wt.%, then it decreases as nano-Mn2O3 wt.% concentration increases. The mechanical properties of (Mn2O3)xSmBa2Cu3O7-δ samples were measured using Vickers microhardness in order to investigate the effect of Mn2O3 nanoparticles on Vickers microhardness number Hv. The Vickers microhardness data were analysed using Meyer's law, Hays and Kendall (HK), and Modified Proportional Specimen Resistance (MPSR) models. The analysis showed that the HK is the best model to describe the load dependence of Hv for all samples. [ABSTRACT FROM AUTHOR]

(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]

YBaCuO superconducting samples were synthesized at different ball-milling times, 0≤ t≤180 min, through the solid-state reaction technique. A comparison between the samples prepared by hand grinding and those prepared by high-speed ball-milling was studied. The variation of relative volume fraction, the lattice parameters, and the average crystallite size with t were examined using X-ray powder diffraction (XRD). The result is that the relative volume fraction of Y-123 phase increases by increasing t up to 15 min, and then it decreases with further increase in t. Moreover, the average crystallite size decreases as t increases from 0 to 60 min and then it increases with further increase in t. In addition, the surface morphology was studied through both scanning and transmission electron microscopes (SEM and TEM). Small crystallite grains, ranging from 25 to 70 nm, were detected between the matrices of Y-123 superconducting phase. The electrical resistivity and transport critical current density for Y-123 samples with different ball-milling time were measured by standard dc four-probe method. The superconducting transition temperature T and the transport critical current density J considerably enhance by increasing t to 15 and 30 min, respectively, beyond which they decrease. The suppression in both T and J may be due to decrease in relative volume fraction or degradation of the crystallite Y-123 matrix, causing increase in grain boundaries resistance. The Vickers microhardness for the prepared samples was measured, and the results indicate that the Vickers microhardness number H increases as the ball-milling time increases. [ABSTRACT FROM AUTHOR]

Solid-state reaction method was used to prepare superconductor samples with nominal composition of (SnO)(BiPb)SrCaCuO, (SnO)(Bi,Pb)-2223 composite, where 0.0 ≤ x ≤ 0.2 wt%. The prepared samples were characterized by X-ray diffraction (XRD) as well as scanning electron microscopy (SEM). XRD patterns proved that the addition of nano-SnO particles to (Bi,Pb)-2223 did not affect the tetragonal structure and the lattice parameters of this phase. Vickers microhardness measurements ( H ) for these samples were carried out at room temperature as a function of applied load, heating temperatures, and dwell time. However, to clarify the indentation size effect (ISE) behavior of these composite materials and to estimate the true microhardness values ( H ), different models including Meyer's law, Hays and Kendall (energy dissipation) model, elastic/plastic deformation model, as well as proportional specimen resistance model were applied. Some important mechanical parameters, such as Young's modulus ( E), yield strength ( Y), fracture toughness ( K), and brittleness index ( B), were estimated from the microhardness curves. It was found that the incorporation of a proper concentration of nano-SnO particles has proved their efficiency to enhance the mechanical properties of superconductors. Moreover, it was noted that dwell time and Vickers microhardness were inversely proportional. Indentation creep experiments showed that the operative creep mechanisms in the studied samples were dislocation creep in addition to dislocation interaction. [ABSTRACT FROM AUTHOR]

To compare between the effect of partial substitution of lead ions (Pb4+ and Pb2+) at thallium (Tl) site in Tl0.8-xHg0.2PbxBa2Ca2Cu3O9−δ superconductor; two different compounds, lead (II) oxide (PbO) and lead (IV) oxide (PbO2), were used for the synthesis of the superconducting samples. Samples with nominal compositions Tl0.8-xHg0.2PbxBa2Ca2Cu3O9−δ, with x = 0.00, 0.05, 0.10, 0.15, and 0.20, were synthesized via solid state reaction technique. The x-ray diffraction (XRD) results showed that the partial substitution of both lead ions has not affected the tetragonal structure. Moreover, the volume fraction was increased from 75.95% to 90.38% and 89.41% as x increased up to 0.20 for PbO and PbO2 substitutions, respectively. The scanning electron microscopy (SEM) images demonstrated better grain connectivity and rectangular-shaped plates, supporting the phase formation of (Tl,Hg)-1223. The energy-dispersive x-ray (EDX) analysis revealed good agreement between the nominal and real compositions. Moreover, the elemental composition and oxidation states were proved by x-ray photoelectron spectroscopy (XPS). Both the superconducting transition temperature (Tc) and critical current (Jc) showed enhancement at x = 0.5 and 0.1 for PbO and PbO2 substituted samples, respectively. Vickers microhardness (Hv) measurements were used to examine the mechanical properties of the composites under a range of applied loads (0.49–9.8 N). All the prepared composites revealed the normal indentation size effect. The proportional sample resistance model proved to be the best model for interpreting the experimental data for the prepared samples. [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]

Superconductor samples of type (CoFeO)GdBaCuO, 0.0≤ x≤0.1 wt.%, were synthesized by the conventional solid-state reaction technique. The prepared samples were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), electrical resistivity, AC magnetic susceptibility, and Vickers microhardness. Phase examination by XRD indicated that the orthorhombic structure of Gd-123 is not affected by nanosized ferrite CoFeO addition, whereas the volume fraction of Gd-123 increased with x up to 0.01 wt.%. Morphological investigations by SEM revealed that the porosity among grains decreased as x increased from 0.0 to 0.1 wt.%. The superconducting transition temperature T was estimated from electrical resistivity and the AC magnetic susceptibility measurements. A reduction in T was observed as x increased from 0.0 to 0.1 wt.%, consisting with the effect of adding magnetic impurities to HTSCs. Room temperature microhardness measurements were carried out at different applied loads (0.5-10 N) for the study of the mechanical performance of the studied samples. The experimental results were analyzed using Meyer's law, Hays-Kendall approach, elastic/plastic deformation model, and proportional specimen resistance model. The results showed that all the samples exhibited normal indentation size effect, and Vickers microhardness values were increased as nanosized CoFeO addition increased. The analysis showed that the proportional specimen resistance model is the best model for computing the load-independent microhardness values of our samples. [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]

In this study, the impact of adding samarium iron garnet (Sm3Fe5O12; SmIG) nanoparticles to the (Bi1.6Pb0.4)Sr1.9Ca0.9Y0.2Cu2.1O8+δ ((Bi, Pb)-2212) superconductor was investigated. The conventional solid-state reaction method was utilized to synthesize (SmIG)x(Bi, Pb)-2212 phase with different concentrations (x = 0, 0.25, 0.5, 0.75, 1, and 2 wt%). The structure, the morphology, and the elemental composition were tested using X-ray powder diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and dispersive X-ray spectroscopy (EDX), respectively. Filling of pores and voids validated the impact of the added nano-SmIG on intergrain connections. The enhancement in oxygen content was verified by iodometric titration analysis. The superconducting transition temperature (Tc) and the critical current density (Jc) showed best enhancement with the addition of nano-SmIG up to x = 0.75 wt%, having values of 91.02 K and 373.95 A/cm2, respectively. The fluctuations in the superconducting properties were explained via X-ray photoelectron spectroscopy (XPS) by studying the elemental composition and oxidation states for all elements. Vickers microhardness (Hv) investigations were carried out at different applied loads and indentation time of 20 s, where Hv reached its highest value at x = 0.25 wt%. Based on Hv values, the modified proportional sample resistance (MPSR) model offered the most suitable theoretical model to elucidate the experimental data. [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]

To manifest the effect of hard magnetic Ba0.5Sr0.5Fe12O19 nanoparticles on the mechanical performance of the (Bi,Pb)-2223 superconducting phase, nano-(Ba0.5Sr0.5Fe12O19)x/Bi1.8Pb0.4Sr2Ca2Cu3.2O10+δ, with x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.10, and 0.20 wt%, were synthesized using a conventional solid-state reaction method. The X-ray diffraction (XRD) data revealed that adding nano-(Ba0.5Sr0.5Fe12O19) to the host (Bi,Pb)-2223 phase preserved the orthorhombic structure. The porosity (P%) calculations revealed a decrease until x = 0.04 wt%, which suggests that the addition of nano-(Ba0.5Sr0.5Fe12O19)x reduces the number of voids and improves inter-grain connections, as confirmed by SEM micrographs. The superconducting transition temperature (Tc) increased to 112 K with the inclusion of nano-(Ba0.5Sr0.5Fe12O19) up to x = 0.04 wt%. Vickers microhardness (HV) measurements were conducted at various applied loads (0.245–9.800 N) and a duration time of 45 s. The HV number increased with the addition of x up to x = 0.04 wt% but then decreased with further addition. Various models were employed for analysis and modelling of Vickers hardness (HV) versus test load (F), including Meyer's law, Hays–Kendall (H–K) model, the elastic/plastic deformation (EPD) model, the proportional sample resistance (PSR) model, the modified proportional sample resistance (MPSR), and indentation-induced cracking (IIC) model. It was found that the PSR model was the most appropriate theoretical model for describing the microhardness of nano-(Ba0.5Sr0.5Fe12O19)x/(Bi,Pb)-2223 composites. Moreover, the elastic modulus (E), yield strength (Y), fracture toughness (K), brittleness index (B), and elastic stiffness coefficient (C11) were estimated as a function of the inclusion of nano-(Ba0.5Sr0.5Fe12O19)x. Furthermore, the indentation creep test (time-dependent Vickers microhardness) revealed that the dislocation creep mechanism exists in composite samples with low concentrations (x < 0.05 wt%), whereas the dislocation climbs creep mechanism was observed for x ≥ 0.05 wt%. [ABSTRACT FROM AUTHOR]

The impact of adding the orthoferrite NdFeO3, at the nanoscale, on the (Cu0.5Tl0.5)Ba2Ca2Cu3O10–δ phase formation, microstructure, electrical and mechanical performance was studied. The nano-(NdFeO3)x/(CuTl)-1223 composites, with x = 0.00, 0.25, 0.50, 0.75, 1.00, and 2.00 wt.%, were prepared using the solid-state reaction technique. The X-ray diffraction (XRD) confirmed that supplementing the host (CuTl)-1223 phase with nano-NdFeO3 did not alter the unit cell parameters (a and c) and preserved the tetragonal structure. SEM micrographs suggested that the inclusion of nano-NdFeO3 reduced the number of voids and boosted the inter-grain connections. The energy-dispersive X-ray (EDX) spectra revealed the elemental compositions of the various superconductor composites. The superconducting transition temperature (Tc) and the critical current density (Jc) increased with the inclusion of nano-NdFeO3 up to x = 0.50 wt.%. X-ray photoelectron spectroscopy (XPS) spectra analysis revealed the elemental composition and oxidation state of all elements. The Vickers microhardness (Hv) measurements were analyzed and compared with five different theoretical models. According to Hv measurements, the modified proportional sample resistance (MPSR) model provided the best theoretical analysis of Hv within the plateau limit regions. Moreover, various mechanical parameters were estimated as a function of the inclusion of nano-NdFeO3. The indentation creep test showed that the composite samples with high nanoparticle concentration (x > 0.50 wt.%) have dislocation creep mechanism, while those with x ≤ 0.50 wt.% followed a dislocation climbs creep mechanism. A comparison between NdFeO3 nanoparticles and other magnetic ferrites and nano-magnetic oxides was reported. [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 (nano-Ag) xCu 0.5Tl 0.5Ba 2Ca 2Cu 3O 10−δ, x=0.0,0.5,1.0,1.5,2.0, and 3.0 wt.% of the total sample’s mass were prepared by a single step solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) and a scanning electron microscope (SEM). The electrical properties of the prepared samples were investigated using the electrical resistivity and I– V measurements. The Vickers microhardness ( Hv) was measured at different applied loads (0.25–3.0 N) for studying the mechanical performance of the prepared samples. All prepared samples exhibited normal indentation size effect (normal ISE) and the Hv number was load dependent. Hv number increases as nano-Ag addition increased. The experimental data of Hv was analyzed using different models; Mayer’s law, Hays–Kendall (H–K) approach, elastic/plastic deformation (EPD) model, proportional specimen resistance (PSR) model, and indentation induced cracking (IIC) model. In addition, the true microhardness ( Ho) values were evaluated through different models. The obtained data has good agreement with the PSR model. Also, Young’s modulus ( E), yield strength ( Y), fracture toughness ( Kf), and brittle index ( Bi) were calculated. [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]

In this study, superconducting samples of type CuTlBaCaCuO,(CuTl)-1223, added by SnO and InO in nano-scale were prepared by a solid-state reaction technique. The concentrations of both SnO and InO were varied from 0.0 to 1.0 wt.% of the total sample's mass. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination, respectively. The electrical resistivity of the prepared samples was measured by the conventional four-probe technique from room temperature down to the zero superconducting transition temperature ( T). An increase in T is observed up to x=0.6 wt.% for (SnO) CuTlBaCaCuO, followed by a systematic decrease with increasing nano-SnO addition for x>0.6 wt.%. While, for (InO) CuTlBaCaCuO the T is slightly changed with x. Room temperature Vickers microhardness measurements were carried out at different applied loads (0.49-2.94 N) for the study of the mechanical performance of the prepared samples and examination of the effect of different nano-oxides addition on the microhardness of (CuTl)-1223 phase. Furthermore, the true microhardness values ( H), for both additions, were evaluated through different models and their results were compared with those estimated from the experimental results in the plateau region. Also, some important mechanical parameters, such as Young's modulus ( E), yield strength ( Y), fracture toughness ( K) and brittleness index ( B), were calculated for both additions. The results clarified that these parameters are strongly dependent on both the applied loads and the nano-oxides addition. [ABSTRACT FROM AUTHOR]

This comparative study sheds light on the optimum addition x of K 5 [SiFe(OH 2)W 11 O 39 ]·14H 2 O ({FeSiW 11 }) and K 6 [(H 2 O)MnSiW 11 O 39 ]·21H 2 O ({MnSiW 11 }) (x = 0.02, 0.04, 0.08, 0.12, 0.16 and 0.20 wt%) nanoparticles to produce the desired mechanical characteristics of the (Bi,Pb)-2223 superconducting phase using a Vickers microhardness (H V) tester. H V measurement was performed at room temperature for different applied loads (0.245–9.8 N) and times (10–60 s). From the H V measurements, all the prepared samples had a normal 'indentation size effect' behaviour. It was found that 0.04 wt% {FeSiW 11 } nanoparticles and 0.08 wt% {MnSiW 11 } nanoparticles were the optimal addition to increase the microhardness of the (Bi,Pb)-2223 phase. Accordingly, other mechanical parameters for potential applications, such as the elastic modulus, yield strength and fracture toughness of the samples studied, were extracted from H V as a function of nanoparticle addition. The measured H V data were theoretically analysed with use of different models. The modified proportional sample resistance model was identified as the best theoretical model to describe the true H V values for both phases. Indentation creep analysis was also performed using time-dependent microhardness to indicate the enhancement of new cavity formation in the measured samples. • The Vickers microhardness of new polyoxometalate–(Bi,Pb)-2223 composites was studied. • The Vickers microhardness was increased by addition of both polyoxometalates. • All measured samples exhibit normal indentation size effect behaviour. • The experimental data are well fitted by the modified proportional sample resistance model. • Enhancement of new cavity formation was implied from indentation creep analysis. [ABSTRACT FROM AUTHOR]