Copper oxide content dependence of crystallization behavior, glass forming ability, glass stability and fragility of lithium borate glasses

Differential thermal analysis (DTA) and X-ray diffraction (XRD) have been employed to investigate the copper oxide content dependence of the glass transition temperatures data, activation energy for the glass transition E(t), glass stability GS, fragility index F(i), the glass-forming ability (GFA) and crystallization behavior of {(100-x)mol% Li(2)B(4)O(7)-xmol% CuO} glass samples, where x=0-40 mol% CuO. From the dependence of the glass transition temperature T(g) on the heating rate beta, the fragility, F(i), and the activation energy, E(t), have been calculated. It is seen that F(i) and E(t) are attained their minimum values at 0 < x < 15 mol% of CuO. The addition of CuO above 15 mol% causes a decrease in the glass-forming ability and the supercooled liquid region SCL. Thermal stability has been monitored through the calculation of the temperature difference T(x)-T(g), SCL region and the GS. The GFA has been investigated on the basis of Hruby parameter K(H), which is a strong indicator of GFA, and the relaxation time. Results of GFA are in good agreement with the fragility index, F(i), calculations indicating that {90Li(2)B(4)O(7) center dot 10CuO} is the best glass former. The stronger glass forming ability has decreasing the fragility index. XRD result indicates that no fully amorphous samples but a mixture of crystalline and amorphous phases are formed in the samples containing x > 25 mol% CuO and below it composed of glassy phase. Increasing the CuO content above 25 mol% helps the crystallization process, and thus promotes a distinct SCL region. XRD suggests the presence of micro-crystallites of remaining residual amorphous matrix by increasing the CuO content. (C) 2009 Elsevier B.V. All rights reserved.