Doping effects of ZrC and ZrB2 in the powder-in-tube processed MgB2 tapes

Abstract

We have investigated the effects of ZrC and ZrB 2 doping on the superconducting properties of the powder-in-tube processed MgB 2 /Fe tapes. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX), transport and magnetic measurements. We confirmed the following quite different roles of ZrC and ZrB 2 in MgB 2 . ZrC doping was found to decrease the transport critical current density (J c ) at 4.2 K, while the critical temperature (T c ) kept constant. In contrast, the J c values in magnetic fields were enhanced greatly by the ZrB 2 addition, which resulted in a decrease in T c by only 0.5 K. The reason for different effects of two dopants is also discussed.Extensive research efforts have been made to improve the performance of MgB 2 materials since the discovery of superconductivity at 39 K in this compound [1] . However, a rapid decrease in critical current density (J c ) at magnetic fields in MgB 2 is the principal limitation to their technological applications. This limitation is strongly correlated to poor grain connection and lack of pinning centers. Hence, chemical doping using different elements/compounds seems to be the best and most practical route [2][3][4][5][6] . Of all the chemical dopings undertaken, Zr and C doping have been successful in enhancing both the irreversibility field (Hirr) and J c (B). The remarkable improvement of J c (B) behavior in the above-doped samples can be explained by the densification effect and the improved pinning [2,4] . The intention of the present work is to study the effect of ZrC and ZrB 2 additions on the phase formation and microstructures of MgB 2 as well as their roles in the J c enhancement. It should be noted that the transitionmetals ZrC and ZrB 2 are potential ceramic materials highly resistant to high temperatures, wear, oxidation and corrosion. They have a very good thermal and electrical conductivity [7] . In this study, we show how ZrC and ZrB 2 affect the properties of MgB 2 tapes made by powder-in-tube technique. We have found quite different behaviors between ZrC and ZrB 2 in MgB 2 .

Development of Doped ${\rm MgB}_{2}$ Wires and Tapes for Practical Applications

“…The effect of metal carbides like ZrC [45], NbC [46], TaC and MoC 2 [47] has been studied in our group. We found that these carbides show little effect on J c , because they are stable in contact with Mg and B even at high temperature; thus no fresh reactive C is available for incorporating into the MgBB 2 lattice during its formation.…”

The Influence of Milling Time and <inline-formula> <tex-math notation="TeX">$\hbox{ZrB}_{2}$</tex-math></inline-formula> Addition on the Superconducting Properties of <inline-formula> <tex-math notation="TeX">$\hbox{MgB}_{2}$</tex-math></inline-formula>

“…ZrB 2 additions, which have the same crystal structure as MgB 2 , were previously studied [14]- [17]. In situ powder-in-tube (PIT) method and heat treatment at 600 • C for 40 min [14], [15], and In situ method followed by swaging, wire drawing, rolling into tapes, and heat treatment at 800 • C for 1 h [16], were used to fabricate MgB 2 + ZrB 2 tapes. Milling mixtures of powders in a SPEX mill for 48 min, pressing into cylindrical pellets in a steel Manuscript die, and heat treating at 700 to 900 • C for 1 h are some steps used to produce MgB 2 +ZrB 2 pellets [17].…”

Otimização das propriedades de transporte em supercondutores de MgB2 com a adição de compostos de estrutura cristalina tipo AlB2 e fontes distintas de carbono

“…Desde a descoberta de supercondutividade no MgB 2 , muitos grupos de pesquisa (CAVA;ZANDBERGEN;INUMARUA, 2003;CANFIELD et al, 2001) (AGATSUMA et al, 2006;YAMAMOTO et al, 2005;WILKE et al, 2004;DOU et al 2003;DOU et al, 2002), devido a uma possível substituição nos sítios de boro pelos átomos de carbono na estrutura cristalina do MgB 2 (MAZIN et al, 2002). Com isso, alguns grupos de pesquisa têm analisado diversos materiais como fonte de carbono: carbono puro (MA, 2006;SOLTANIAN et al, 2003a), grafite (SENKOWICZ et al, 2005XU et al, 2004a), nanotubos de carbono (SERRANO et al, 2008;SERQUIS et al, 2007;YEOH et al, 2004;SERQUIS et al, 2003, DOU et al, 2002a), diamante (ZHAO et al, 2003), carbono nanohorns (BAN et al, 2005), carbeto de silício (VINOD et al, 2009;SERRANO et al, 2008;AGATSUMA et al, 2006;SOLTANIAN et al, 2005;DOU et al, 2002) e mais recentemente os compostos orgânicos (ZHANG et al, 2009;KIM et al, 2006;YAMADA et al, 2006).…”