IMPACT OF NANO-<font>Mo</font> ADDITION/SUBSTITUTION ON THE PHASE FORMATION AND SUPERCONDUCTIVITY OF <font>Mg</font>1-x<font>Mo</font>x<font>B</font>2 (x=0.0to 0.50)

Bulk polycrystalline samples of nano- Mo doped MgB 2 were synthesized by Fe tube encapsulation at ambient pressure under argon annealing (850&#176;C). Mo substitution takes place successfully at the Mg site in Mg 1-x Mo x B 2 only till x=0.2. For higher (x&gt;0.2) Mo content the same did not enter the MgB 2 lattice but rather forms an isomorphic lattice in the host with decreased c but an increased a-parameter. The ρ(T) measurements showed superconducting transition temperature (T c ) of around 36 K for all the samples till x=0.3 and slightly decreased values of 35 and 34 K for x=0.4 and 0.5 samples, respectively. Resistivity under magnetic field [R(T)H] experiments showed distinct single peaks in dρ/dT for all applied fields up to 8 Tesla. The estimated upper critical field H c2 is 8 Tesla for pristine and x=0.2 samples at 15.6 and 19 K, respectively. Thus H c2 increases up to x=0.20 samples and decreases afterwards. Magnetic susceptibility measurements exhibited sharp transition to superconducting state with a sizeable diamagnetic signal at 38 K (T c ) in zero field-cooled measurements. Commendable current density (J c ) of up to 105 A/cm2 in 1–2 T (Tesla) fields at temperatures (T) of up to 10 K is seen from magnetization measurements invoking the Bean&#39;s critical state model for pristine samples. For higher fields above 2.5 Tesla the J c (H) characteristics of x=0.1 and 0.2 samples were found to be slightly superior to that for pristine samples with enhanced H irr (irreversibility field).