Influence of Metal Diboride and Dy(2)O(3) Additions on Microstructure and Properties of MgB(2) Fabricated at High Temperatures and under Pressure

High temperatures and under pressure (HTP) processing has been used to study the effects of chemical doping in MgB(2.) ZrB(2), TiB(2) and NbB(2) were selected as additives since, like MgB(2), they have an AlB(2)-type structure and similar lattice parameters. Dy(2)O(3) was selected as it has been reported to generate nanoscale, secondary intragrain phases in MgB(2). While C is known to enter the B-sublattice readily, attempts to dope Zr and other elements onto the Mg site have been less successful due to slow bulk diffusion, low solubility in MgB(2), or both. We have used high-temperature, solid-state sintering (1500 °C), as well as excursions through the peritectic temperature (up to 1700 °C), to investigate both of these limitations. Bulk MgB(2) samples doped with MB(2) (M = Zr, Ti and Nb) and Dy(2)O(3) additions were synthesized and then characterized. Lattice distortion and high densities of crystal defects were observed in the MgB(2) grains around nano-sized MB(2) inclusions, this highly defected band contributed to a large increase in B(c2) but was not large enough to increase the irreversibility field. In contrast, distributed intragrain precipitates were formed by Dy(2)O(3) additions which did not change the lattice parameters, T(c), T(c) distribution or B(c2) of MgB(2), but modified the flux pinning.