Flux Pinning Optimization of ${\rm MgB}_{2}$ Bulk Samples Prepared Using High-Energy Ball Milling and Addition of ${\rm TaB}_{2}$

MgB
₂
is considered to be an important conductor for applications. Optimizing flux pinning in these conductors can improve their critical currents. Doping can influence flux pinning efficiency and grain connectivity, and also affect the resistivity, upper critical field and critical temperature. This study was designed to attempt the doping of MgB
₂
on the Mg sites with metal-diborides using high-energy ball milling. MgB
₂
samples were prepared by milling pre-reacted MgB
₂
and TaB
₂
powders using a Spex 8000 M mill with WC jars and balls in a nitrogen-filled glove box. The mixing concentration in (Mg
_1-x
Ta
_x
)B
₂
was up to x = 0.10. Samples were removed from the WC jars after milling times up to 4000 minutes and formed into pellets using cold isostatic pressing. The pellets were heat treated in a hot isostatic press (HIP) at 1000degC under a pressure of 30 kpsi for 24 hours. The influence that milling time and TaB
₂
addition had on the microstructure and the resulting superconducting properties of TaB
₂
-added MgB
₂
is discussed. Improvement of J
_c
at high magnetic fields and of pinning could be obtained in milled samples with added TaB
₂
. The sample with added 5at.%TaB
₂
and milled for 300 minutes showed values of J
_c
~ 7 times 10
⁵
A/cm
²
and F
_p
~ 14 GN/m
³
at 2 T, 4.2 K. The milled and TaB
₂
-mixed samples showed higher values of mu
₀
H
_irr
than the unmilled-unmixed sample.