Formation and crystal growth of needle-like rutile in glass- ceramics

Glass-ceramic, which has negligible dielectric loss, high mechanical strength, excellent drop resistance, low CTE, and low density for lightweight design, is the best option for the back cover of mobile devices in the 5 G era. Herein, the effect of P 2 O 5 on the phase separation and crystallization of MgO–Al 2 O 3 –SiO 2 -TiO 2 glass-ceramics is studied. The incorporation of P 2 O 5 in the glass structure leads to phase separation, in which the P and Mg-enriched phase was formed in the glass matrix, and promotes the increase of T g . With the increase of P 2 O 5 content, the precipitated crystals change significantly. First, the silicate crystals (Mg 2 SiO 4 ) disappear, whereas the phosphate crystals (LiMgPO 4 ) emerge when 2 mol% P 2 O 5 is introduced. Second, titanate crystal (MgTi 2 O 5 ) can not be observed when 4 mol% P 2 O 5 is introduced. The Ti 5 O 9 crystals appear simultaneously with LiMgPO 4 crystals and transform to rutile TiO 2 crystals at high temperature. Interestingly, the needle-like rutile TiO 2 crystals, which is 300 nm long and 20 nm wide, have been found in a glass with 4 mol% P 2 O 5 . The large L/D ratio of needle-like crystals increases the hardness significantly from 6.08 GPa to 7.14 GPa. Similar to other fiber reinforced composites, this needle-like crystals provide a new strategy to improve the mechanical properties of glass ceramics.