A series of TeO2?PbO glasses were fabricated with increasing fractions of mixed alkali, alkaline earth, and lanthanide chlorides. The glass and crystal structure was studied with Raman spectroscopy, nuclear magnetic resonance (NMR), X-ray diffraction, and electron microscopy. As the chloride fraction increased, the medium-range order in the glass decreased up to a critical point (?14 mass% of mixed chlorides), above which the glasses became phase-separated. Resulting phases were a TeO2/PbO-rich phase and a crystalline phase rich in alkali chlorides. Contrary to previous studies, the 125Te NMR indicates that the Te site distribution did not change with increased concentrations of M+, M2+, and M3+ cations, but rather is controlled by the Te/Pb molar ratio. The 207Pb NMR shows that two Pb species exist and their relative concentration changes monotonically with the addition of mixed chlorides, indicating that the additives to the TeO2?PbO glass are accommodated by changing the Pb species. The 23Na and 35Cl NMR indicate that Na and Cl are distributed in the single-phase glass up to the critical point and, at higher concentrations, partition to crystalline phases. At the 14 mass% loading, transmission electron microscopy shows that the sample contains ?10 nm seed nuclei that increase in size and concentration with exposure to the electron beam.