Effects of Boron Purity, Mg Stoichiometry and Carbon Substitution on Properties of Polycrystalline MgB$_{2}$

R. A. Ribeiro; S. L. Bud'ko; C. Petrovic; P. C. Canfield

doi:10.1016/S0921-4534(02)02326-2

paper

Effects of Boron Purity, Mg Stoichiometry and Carbon Substitution on Properties of Polycrystalline MgB $_{2}$

arXiv:cond-mat/0212385 · doi:10.1016/S0921-4534(02)02326-2

Abstract

By synthesizing MgB $_{2}$ using boron of different nominal purity we found values of the residual resistivity ratio ( $R R R = R (300 K) / R (42 K)$ ) from 4 to 20, which covers almost all values found in literature. To obtain high values of $R R R$ , high purity reagents are necessary. With the isotopically pure boron we obtained the highest $R R R \sim$ 20 for the stoichiometric compound. We also investigated Mg $_{x}$ $^{11}$ B $_{2}$ samples with 0.8 $< x <$ 1.2. For the range Mg $_{0.8}$ $^{11}$ B $_{2}$ up to Mg $_{1.2}$ $^{11}$ B $_{2}$ we found average values of $R R R$ between 14 and 24. For smaller variations in stoichiometry ( $x = 1 \pm 0.1$ ) $R R R = 18 \pm 3$ . All of our data point to the conclusion that high $R R R$ ( $\sim 20$ ) and low $ρ_{0}$ ( $\leq 0.4 μ Ω c m$ ) are intrinsic material properties associated with high purity MgB $_{2}$ . In addition we have performed initial work on optimizing the formation of carbon doped MgB $_{2}$ via the use of B $_{4}$ C. Nearly single phase material can be formed by reaction of nominal Mg(B $_{0.8}$ C $_{0.2}$ ) $_{2}$ for 24 hours at $120 0^{\circ} C$ . The $T_{c}$ for this composition is between $21.9 K$ and $22.7 K$ (depending on criterion).

accepted to Physica C, special MgB2 issue

Effects of Boron Purity, Mg Stoichiometry and Carbon Substitution on Properties of Polycrystalline MgB2​

Abstract

Effects of Boron Purity, Mg Stoichiometry and Carbon Substitution on Properties of Polycrystalline MgB $_{2}$