In one aspect the disclosure is directed to a binary silica-titania blank having a CTE of 0 ± 30 ppb/°C or less and a insert made of silica-titania-dopant(s) glass in the critical zone, wherein the dopants are selected from the group consisting of aluminum oxide, selected transition metal oxides, and amount of the dopants is in the range of 0.05 wt.% to 8 wt.% and the insert is fusion bonded to the blank with or without a frit. In various embodiments the dopants are selected from the group consisting of 0.25 wt.% to 8 wt.% Al 2 O 3 , 0.05 wt.% to 3 wt.% Nb 2 O 5 , and 0.25 wt.% to 6 wt.% Ta 2 O 5 .