Role of double doping with C and RE2O3 oxides on the critical temperature and critical current of MgB2 phase

A series of MgB2 samples doped with C, RE2O3 oxides (RE = Ce, Nd), and C and RE2O3oxides was prepared by the hot isostatic pressing method at high pressure: 1 GPa under argon gas. Based on X-ray diffraction and magnetization measurements it was found that the RE2O3 is not incorporated into MgB2. A secondary REB4 phase is present after the synthesis. No decrease in the critical temperature (Tc) is observed after the RE2O3 doping. The Tc of C and RE2O3 doped MgB2 is decreased by 3 K. The doping decreases the diamagnetic response in comparison to pure MgB2 phase. The highest critical current density (Jc) was 3.4 × 105 A/cm2 at 4.2 K and 0.5 T for the bulk material, and the irreversibility field for the Nd2O3 doped sample was located at high field at T = 30 K. The results indicate that inside grains of pinning centers increase Jc from 4.2 K to 25 K and decrease Jc at 30 K. On the other hand, pinning centers between grains (precipitate) increase Jc at 30 K and decrease Jc from 4.2 K to 25 K in the middle and high magnetic fields. Our research shows that carbon-encapsulated boron creates a point pinning centers.