The purpose of this paper is to study the glass formation tendency in the ternary system B2O3―Bi2O3―MoO3
and to define the main structural units building the amorphous network. A wide glass formation area was
determined which is situated near the Bi2O3―B2O3 side. A liquid phase separation region was observed near
the MoO3―B2O3 side for compositions containing below 25 mol% Bi2O3 and their microheterogeneous
structure was observed by SEM. The phase formation was characterized by X-ray diffraction (XRD). By DTA was
established the glass transition temperature (Tg) in the range of 380–420 °C and crystallization temperature
(Tx) vary between 420 and 540 °C. The main building units forming the amorphous network are BO3 (1270 and
1200 cm−1), BO4 (930–880, 1050–1040 cm−1), MoO4 (840–760 cm−1) and BiO6 (470 cm−1). It was proved
that Bi2O3 favors the BO3→BO4 transformations while MoO3 preserves BO3 units in the amorphous network.