Patent ID: 7189668

Claim:
A process for manufacturing glass-ceramic materials in the BaO—La 2 O 3 —SiO 2 system that possess a softening temperature above 1000° C. and a thermal expansion coefficient in excess of 10×10 −6 ° C. −1 when measured over the range 20–1000° C., comprising manufacturing said materials by thermal treatment of a precursor glass powder at a temperature in excess of 900° C. and converting said powder to a substantially crystalline glass ceramic material wherein said powder comprises, on a weight percent basis, 10–55% BaO, 3–50% La 2 O 3 −25–48% SiO 2 , less than 5% Al 2 O 3 and less than 1% B 2 O 3 .