Positron Spectroscopy of Boron Carbide Containing Metal Impurity

Boron carbide (B 4.3 C) semiconductors with metal incorporation were prepared by hot pressing mixtures of boron carbide powder (B 4.3 C) and 0.5 ∼ 1 at% metal (Zr or V). The influences of impurity incorporation on the subtle structure and conductivity of B 4.3 C crystals were investigated. Positron lifetime spectrum, x-ray diffraction and Doppler-broadening analyses indicate that appropriate metal introduction can modify the B 4.3 C structure. Especially, noticeable vacancies are introduced into about the B(3) sites at the chain centers. Meanwhile, the B 4.3 C lattice cell contracts a little along the c axis. No distinctive change of the electrical conductivity is found to accompany the structural change.