Microstructure and phase composition of hypoeutectic Te–Bi alloy as evaporation source for photoelectric cathode

Abstract

A hypoeutectic 60Te–40Bi alloy in mass percent was designed as a tellurium atom evaporation source instead of pure tellurium for an ultraviolet detection photocathode. The alloy was prepared by slow solidification at about 10−2 K·s−1. The microstructure, crystal structure, chemical composition, and crystallographic orientation of each phase in the as-prepared alloy were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. The experimental results suggest that the as-prepared 60Te–40Bi alloy consists of primary Bi2Te3 and eutectic Bi2Te3/Te phases. The primary Bi2Te3 phase has the characteristics of faceted growth. The eutectic Bi2Te3 phase is encased by the eutectic Te phase in the eutectic structure. The purity of the eutectic Te phase reaches 100wt% owing to the slow solidification. In the eutectic phases, the crystallographic orientation relationship between Bi2Te3 and Te is confirmed as $${[0001]_{B{i_2}T{e_3}}}//{[1\bar 21\bar 3]_{Te}}$$ and the direction of Te phase parallel to $${[11\bar 20]_{B{i_2}T{e_3}}}$$ is deviated by 18° from Te $$N{(2\bar 1\bar 11)_{Te}}$$ .