Effect of Y₂BaCuO₅ on fracture toughness of YBCO prepared by a MPMG process

The fracture toughness of melt-powder-melt-growth (MPMG) processed YBaCuO samples was measured and the effect on the fracture toughness of the dispersed Y₂BaCuO₅ (211) particles in the 123 superconducting phase was found. Preferred fracture planes were the (100), (010) and (001) planes, and the fracture toughness of the (001) plane was lower than those of the (100) and (010) planes. The indentation fracture method indicated that K_c = 0.88-1.2 MPa m ^{1 2} in an inert environment for YBaCuO crystals without the 211 particles, when the crack plane is the (100) plane or the (010) plane. The presence of the 211 particles in the 123 matrix increased the fracture toughness in this direction up to 1.6-2.1 MPa m ^{1 2}.