Bond Switching in Densified Oxide Glass Enables Record-High Fracture Toughness

Abstract

Humans primarily interact with information technology through glass touch screens, and the world would indeed be unrecognizable without glass. However, the low toughness of oxide glasses continues to be their Achilles heel, limiting both future applications and the possibility to make thinner, more environmentally friendly glasses. Here, we show that with proper control of plasticity mechanisms, record-high values of fracture toughness for transparent bulk oxide glasses can be achieved. Through proper combination of gas-mediated permanent densification and rational composition design, we increase the glasses’ propensity for plastic deformation. Specifically, we demonstrate a fracture toughness of an aluminoborate glass (1.4 MPa m0.5) that is twice as high as that of commercial glasses for mobile devices. Atomistic simulations reveal that the densification of the adaptive aluminoborate network increases coordination number changes and bond swapping, ultimately enhancing plasticity and toughness upon fracture. Our findings thus provide general insights into the intrinsic toughening mechanisms of oxide glasses.

High-entropy R2O3-Y2O3-TiO2-ZrO2-Al2O3 glasses with ultrahigh hardness, Young's modulus, and indentation fracture toughness

“…Notably, the fracture toughness of R = La, Sm, and Gd glass is 1.21 MPa$m 0.5 , 1.39 MPa$m 0.5 , and 1.52 MPa$m 0.5 , respectively, which is much larger than the values of current commercially available oxide glasses, such as silicates, borates, borosilicate, etc., which is reported to be lower than 1 MPa$m 0.5 (Quinna and Swab, 2013;To, 2019;Østergaard et al, 2019;Rouxel and Yoshida, 2017;Yao, 2016;Scannell et al, 2017;Vullo and Davis, 2004;Wiederhorn et al, 1974;Mezeix, 2017;Kato et al, 2010;Reddy et al, 1988), as shown in Figure 5C (areas below the gray short dash line). Currently, the highest fracture toughness of oxide glasses is reported to be 1.36 MPa m 0.5 using the single-edge pre-cracked beam method (To et al, 2021). In this work, the measured fracture toughness of R = Sm and Gd glass exhibits an almost comparable value to that of maximum record.…”

“…Among metallic oxides, alumina (Al 2 O 3 ) possesses the highest dissociation energy (G Al2O3 = 133.8 kJ/cm 3 ) (Makishima, 1973). Hence, it is reasonable that the glasses with high hardness, high Young's modulus, and high fracture toughness contain a great quantity of Al 2 O 3 , as reported in R 2 O 3 -Al 2 O 3 -SiO 2 glasses (R = rare earth ion, Y, or Sc) and 25Li2O-20Al2O3-55B2O 3 glass (Stevensson and Edé n, 2013;Johnson et al, 2005;Du, 2009;Inaba et al, 2000;To et al, 2021). The atomic packing density of glass increases with the coordination number of Al and decreases with the ionic volume of oxide components.…”

“…As exhibited in Figure 6D, the fractions of Al [4] , Al [5] , and Al [6] are estimated to be 55.3%, 31.0%, and 13.7%, respectively, which are much higher than the values of commercial oxide glasses. Figure 7A shows the effect of entropy on the fracture toughness (K IC ) of oxide glasses (To et al, 2021;Yao, 2016;Scannell et al, 2017;Vullo and Davis, 2004;Wiederhorn et al, 1974;Mezeix, 2017;Kato et al, 2010;Reddy et al, 1988). Interestingly, although there are differences in composition, the fracture toughness values of glasses show a tendency of increases with the increase of entropy, which indicates that the fracture toughness of oxide glass may be related to entropy.…”

“…As presented in Figure 5C, the prepared high-entropy glasses exhibit extraordinary fracture toughness compared with the commercial oxide glasses (borates, silicates, borosilicates, etc. [To et al, 2021;Yao, 2016;Scannell et al, 2017;Vullo and Davis, 2004;Wiederhorn et al, 1974;Mezeix, 2017;Kato et al, 2010;Reddy et al, 1988]) and the current high fracture toughness oxide glasses (To et al, 2021;Dé riano et al, 2004). The dissociation energy of the widely used oxides on conventional glasses, such as B 2 O 3 , SiO 2 , P 2 O 5 , and alkali metal oxides, is 77.8 kJ/cm 3 , 64.4 kJ/cm 3 , 62.7 kJ/cm 3 , and 23.4-83.6 kJ/cm 3 , (23.4 kJ/cm 3 for K 2 O, 37.2 kJ/cm 3 for Na 2 O, 40.5 kJ/cm 3 for BaO, 48.5 kJ/cm 3 for SrO, 64.8 kJ/cm 3 for CaO, and 83.6 kJ/cm 3 for MgO) respectively (Makishima, 1973).…”

“…Interestingly, although there are differences in composition, the fracture toughness values of glasses show a tendency of increases with the increase of entropy, which indicates that the fracture toughness of oxide glass may be related to entropy. The increased fracture toughness in a constant entropy on the areas where the upward arrows are located is due to the increased pressure during the preparation process, which translate the low coordinated B (B [3] ) and Al (Al [4] ) to high coordinated B (B [4] ) and Al (Al [5] , Al [6] ), respectively (To et al, 2021). The improved fracture toughness by entropy may be speculated to the bending growth of cracks due to the complex interaction between atoms.…”