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Table 3 Properties comparison of F2, SF6 glass (Schott), and NC-21A (ITME)

From: Modification of borosilicate glass composition for joint thermal processing with lead oxide glasses for development of photonic crystal fibers

Parameter NC-21A F2 SF6
Refractive index \(\hbox {n}_\mathrm{{d}}\) 1.526 1.620 1.805
Linear thermal expansion coefficient for the range of 20–250  \(^{\circ }\hbox {C}\, \alpha \,[10^{-7}\, \hbox {K}^{-1}]\) 87.2 91.9 90.3
Lower annealing temperature \(\hbox {t}_{d}\,[^{\circ }\hbox {C}]\, \hbox {log}\upeta =14.6\) 462 400 405
Transformation temperature \(\hbox {T}_{g}\, [^{\circ }\hbox {C}]\, \hbox {log}\upeta =13.4\) 487 431 442
Upper annealing temperature \(\hbox {t}_{g}\, [^{\circ }\hbox {C}]\, \hbox {log}\upeta =13\) 496 440 450
Dilatometric softening point DTM \([^{\circ }\hbox {C}]\, \hbox {log}\upeta =11.0\) 527 480 463
Characteristic temperatures determined in Leitz heating microscope \([^{\circ }\hbox {C}]\)
   Oval of the sample \(\hbox {T}_\mathrm{{z}}\quad \hbox {log}\upeta =9.0\) 580 520 520
   Sphere creation \(\hbox {T}_\mathrm{{k}} \quad \hbox {log}\upeta =6.0\) 670 620 600
   Hemisphere creation \(\hbox {T}_\mathrm{{pk}} \quad \hbox {log}\upeta =4.0\) 740 820 665
   Spread of the sample \(\hbox {T}_\mathrm{{r}}\quad \hbox {log}\upeta =2.0\) 860 1,130 880