Comparative study on the effect of adding two transition-metal-substituted polyoxometalates on the mechanical properties of the (Bi,Pb)-2223 superconducting phase

Abstract

This comparative study sheds light on the optimum addition x of K5[SiFe(OH2)W11O39]·14H2O ({FeSiW11}) and K6[(H2O)MnSiW11O39]·21H2O ({MnSiW11}) (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 (HV) tester. HV measurement was performed at room temperature for different applied loads (0.245–9.8 N) and times (10–60 s). From the HV measurements, all the prepared samples had a normal ‘indentation size effect’ behaviour. It was found that 0.04 wt% {FeSiW11} nanoparticles and 0.08 wt% {MnSiW11} 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 HV as a function of nanoparticle addition. The measured HV 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 HV 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.