  The synthesis of MgB2-based materials under high pressure gave the
possibility to suppress the evaporation of magnesium and to obtain near
theoretically dense nanograined structures with high superconducting, thermal
conducting, and mechanical characteristics: critical current densities of
1.8-1.0 \cdot 106 A/cm2 in the self field and 103 A/cm2 in a magnetic field of
8 T at 20 K, 5-3 \cdot 105 A/cm2 in self field at 30 K, the corresponding
critical fields being HC2 = 15 T at 22 K and irreversible fields Hirr =13 T at
20 K, and Hirr =3.5 T at 30 K, thermal conduction of 53+/-2 W/(m \cdot \kappa),
the Vickers hardness Hv=10.12+/-0.2 GPa under a load of 148.8 N and the
fracture toughness K1C = 7.6+/-2.0 MPa m0.5 under the same load, the Young
modulus E=213 GPa. Estimation of quenching current and AC losses allowed the
conclusion that highpressure-prepared materials are promising for application
in transformer-type fault current limiters working at 20-30 K.
