Addition of BaHfO 3 (BHO) nano-rods as pinning centers into a GdBa 2 Cu 3 O y (GdBCO) coated conductor dramatically improves the critical current properties in high magnetic fields. This is partly ascribed to the strong flux pinning of these pinning centers. In this paper it is reported that this improvement is mainly caused by unexpected enhancement of the upper critical field, B c2 . The mechanism of the enhancement of B c2 is not yet clear, although the strain around the interface between the pinning center and the superconducting matrix or the interface itself may scatter electrons. This result suggests that the critical current property of REBa 2 Cu 3 O y (RE: rare earth elements, REBCO) coated conductors could be designed not only by tailoring the microstructure of pinning centers but also by controlling the intrinsic superconducting property. Especially, the selection of pinning material and its content that determines B c2 is expected to be a key problem for further improvement of the pinning performance at high magnetic fields.

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