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Reducing the mid-infrared attenuation loss due to absorption of hydroxyl (OH) groups and scattering of metallic Pb species for lead-germanate glass is essential to pave the way for their applications as low-loss mid-infrared fiber optics. In the first part of this study, we report the understanding of the factors that determine dehydration efficiency and metallic Pb formation during the lead-germanate glassmelting process. Combining a dry O 2-rich atmosphere containing ultra-dry N 2 together with the use of chloride dehydration agent and nitrate oxidation agent compound was found to enable efficient dehydration effect and absence of metallic Pb scattering sources in the dehydrated glasses. This glassmelting procedure overcomes previous limitations on the preparation of similar kinds of heavy-metal oxide glasses, where only pure O 2 atmosphere was used and/or use of fluoride dehydration agent deteriorated the glass thermal stability. This work provides guidance for developing other low-loss mid-infrared glasses/fibers containing multivalent heavy-metal ions such as Pb, Bi, Te, Sb, etc K E Y W O R D S dehydration, lead-germanate glass, metallic Pb, mid-infrared fiber optics, scattering loss Note: The sample ID (ie V#-W#-X#-Y#-Z) include glass composition (type and content of chloride dehydration agent), melting conditions and melting atmospheres, and their detailed definitions are as follows: V: S = no NaCl, no PbCl 2 ; P = with PbCl 2 ; N = with NaCl; with #: molar concentration (mol%) of the dehydration agent, PbCl 2 or NaCl. W = Batch-in-temperature: (A) 650°C; (B) 1250°C; (C) 650°C without chlorides, then added PbCl 2 /NaCl at 1250°C; with # = melting time at 1250°C: (1) 40 min; (2) 80 min; (3) 120 min. X = dry gas type: (O) O 2 ; (ON) O 2 + N 2 ; (N) N 2 ; (A) Ar; with # = dry gas flow rate: (2) 1.6 L/min, (4) 4 L/min, (10) 10 L/min, (16) 16 L/min. Y = N * : use of ultra-dry N 2 ; with # = (1) 35 min, (2) 70 min, (3) 105 min GBP time. Z = O * : release of super-dry O 2 in the glass melt via use of NaNO 3 instead of Na 2 CO 3 in glass batch.

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