Enhanced flux pinning in Zr-doped MgB2 bulk superconductors prepared at ambient pressure

Abstract

We prepared a series of Mg 1Ϫx Zr x B 2 bulk samples with different x values by the solid-state reaction at ambient pressure and investigated the effects of the Zr doping on phase compositions, microstructure, and flux pinning behavior. The results indicate that the a axis increases with the increase of the Zr doping and the c axis remains unchanged. ZrB 2 phases form and a small amount of Zr atoms may substitute Mg in Zr-doped samples. Critical temperature drops with increasing the Zr doping. It is found that critical current density J c can be significantly enhanced by the Zr doping and the best data are achieved in Mg 0.9 Zr 0.1 B 2 . For this sample, J c values are remarkably improved to 1.83ϫ10 6 A/cm 2 in the self field and 5.51ϫ10 5 A/cm 2 in 1 T at 20 K. Also, the irreversibility field is increased by the Zr doping. The high density, fine grain size of MgB 2 , and small ZrB 2 particles in Zr-doped samples may be responsible for the enhancement of J c . Also, the field dependence of J c at different temperatures was briefly discussed.

The effect of Pr6O11 doping on superconducting properties of MgB2

“…Chemical doping is an effective method for introducing flux pinners in a superconductor. Various nanoparticles and materials such as C, diamond, SiC, SiO 2 , Ti, Zr, Fe, Ag, 10–17 and some organic compounds have been introduced in MgB 2 . These dopants improved the flux pinning and J c ( H ) of MgB 2 to different extents.…”

Vortex pinning properties and microstructure of MgB2heavily doped with titanium group elements

“…Furthermore, the Zr-doping also offered the enhanced J c characteristics [17]. The optimal Ti-and Zr-doping level of 10% was found in the literatures [15,17,19]. Goto et al claimed that the Zr-and Hfdoping were more effective to enhance the J c -properties than the Ti-doping and obtained the maximized J c at the doping level of 1%-2% [18].…”

“…The pioneering work, which examined the Ti-doping effects, showed that the three orders magnitude larger J c was achieved for the Ti10%-doped MgB 2 sample compared to that of the non-doped one [15]. Furthermore, the Zr-doping also offered the enhanced J c characteristics [17]. The optimal Ti-and Zr-doping level of 10% was found in the literatures [15,17,19].…”

“…Substituting carbon (C), derived from various carbon sources including SiC [11], B 4 C [12], the fullerene (C 60 ) [13], carbohydrates [14] and so on, for the B-site enhances the upper critical field, m H 0 c2 , by shortening the coherence length, resulting in the highly enhanced J c in higher magneticfields. In addition to the carbon, the doping of titanium group elements (TGE; Ti, Zr, Hf) also significantly improved the J c -properties of MgB 2 under high magnetic fields [8,[15][16][17][18][19], in which the optimal TGE-doping level of 1%-20% depended on the species of TGE. The pioneering work, which examined the Ti-doping effects, showed that the three orders magnitude larger J c was achieved for the Ti10%-doped MgB 2 sample compared to that of the non-doped one [15].…”

Superconducting Characteristics of Polycrystalline Magnesium Diboride Ceramics Fabricated by a Spark Plasma Sintering Technique

“…In addition, the chemical doping of secondary phases 12 or proton irradiation techniques 13 have been used to introduce flux pinning centers into MgB 2 to inhibit a rapid drop of the critical current density ( J c ) that occurred at high magnetic fields. In fact, it was reported that Zr‐doping achieved a high J c of 5.7 × 10 5 A/cm 2 at 5 K in a 2 T magnetic field because of the strong pinning effect 14 …”