The density, porosity, and microstructures of MgB2 samples are very important factors for
transition critical current density. The effect of heat-treatment temperatures on density and
porosity in MgB2 superconductors has been investigated. The open porosity increases with
increasing heat-treatment temperatures, but close porosity decreases. The calculated theory
densities from the lattice parameters of the measured samples are 2.6–2.63 g/cm3. The
average measured total porosity (including open and close porosity) is about 50%.