Flux-pinning properties of nanocrystalline HfO₂ added YBa₂ Cu₃ O_7−δ superconductor

Abstract

The effect of addition of different weight percentages of nanocrystalline HfO2, synthesized through a modified combustion method in bulk coarse‐grained orthorhombic YBa2Cu3O7−δ powder was studied. The structure and microstructure of the samples examined by X‐ray diffraction (XRD) and scanning electron microscopy (SEM) showed the formation of a secondary phase YBa2HfO5.5 in the superconductor without deteriorating the superconducting properties. The variation of sintering temperature, density, critical transition temperature (Tc), magnetic field dependence of critical current density (Jc), and flux‐pinning force (Fp) of YBa2Cu3O7−δ having different proportions of YBa2HfO5.5 formed in the matrix were studied in detail. The samples showed a transition temperature (Tc) of ∼92 K and the self‐field critical current density (Jc) increases significantly up to an optimum value of 5.42 × 104 A cm−2 for 2 wt% addition of nano HfO2. The enhancement of the critical current density in the YBa2Cu3O7−δ‐HfO2 samples is attributed to the presence of the nonreacting YBa2HfO5.5 phase, formed due to the addition of HfO2 as artificial pinning center. The formation of YBa2HfO5.5 in YBa2Cu3O7−δ bulk superconductor also enhances the pinning force density from 3 × 106 to 30.4 × 106 N m−3 at 77 K.

Influence of YBa 2 HfO 5.5 – ‘derived secondary phase’ on the critical current density and flux-Pinning force of YBa 2 Cu 3 O 7−δ thick films

“…Due to the complexity of defects in polycrystalline superconductors several different pinning mechanisms may exist which are simultaneously active in polycrystalline high T c superconductors such as: dl pinning, due to the scatter of electron free path caused by the non-superconducting particles of the coherence length (n) embedded in the superconducting matrix and dj pinning, due to a spatial scatter of superconducting T c throughout the sample caused by other superconducting phases causing fluctuation in T c . However the optimum J c value observed for nano HfO 2 and BaHfO 3 added YBCO bulk in our earlier reports [27][28][29] was too low (in the ranges of 10 4 A/cm 2 ) compared to the present set of values (in the ranges of 10 6 A/cm 2 ).…”

“…Similarly, rapid enhancement in flux pinning and critical current density was observed in YBCO films by the incorporation of nanoparticles such as BaSnO 3 [9], BaHfO 3 [22] Ba 2 YTaO 6 [23], Ba 2 YNbO 6 [24,25] and Ba 2 RETaO 6 [26]. In our earlier works, we had reported the effect of addition of simple oxide, HfO 2 [27], ABO 3 type perovskite, nano BaHfO 3 [28,29] and double perovskite YBa 2 HfO 5.5 [30] tremendous improvement in flux pinning force and critical current density.…”

“…The combustion product was subsequently characterized as single-phase nanocrystals of YBa 2 HfO 5.5 [30]. Similar methods were followed for the preparation of HfO 2 [27] and BaHfO 3 [33] and are reported elsewhere.…”

Structural and Superconducting Properties of Thermal Treatment-Synthesised Bulk YBa2Cu3O7−δ Superconductor: Effect of Addition of SnO2 Nanoparticles

“…Unfortunately, bulk Y-123 suffers from low grain boundary conductivity, i.e., weak links and poor flux pinning, resulting in low J c in the presence of magnetic field [3], and its T c is sensitive to oxygen content in the system [4]. Therefore, many efforts have been devoted to overcoming these issues in order to achieve the J c and T c required for technological applications [5,6].…”

Electrical Transport and Lowered Percolation Threshold in YBa2Cu3O7−δ-Nano-YBa2ZrO5.5 Composites

“…It was reported that perovskites could be beneficial for incorporation into YBCO due to their similar crystal structures relative to the host YBCO phase [9]. Thereafter perovskite based additions have gained renewed interest as a class of materials that can be incorporated into REBCO superconductor for dramatic improvements in the pinning properties [10][11][12][13]. And a number of perovskites like Sr 2 HoHfO 5.5 [14], GdBa 2 NbO 6 [15], Ba 2 ErZrO 5.5 [16], YBa 2 ZrO 5.5 [17], and so forth were being considered as substrate materials for YBCO film deposition.…”