Nano- and micro-indentation studies on lithium borate–barium bismuth niobate glasses

The structure and mechanical properties of multifunctional lithium tetra-borate based glasses and glass–ceramics of the system $(100-x) Li_2B_4O_7-x(Bao-Bi_2O_3-Nb_2O_5)$ with x = 10, 20 and 30 in molar ratio, have been characterized. Nano- and micro-indentation techniques were employed to evaluate the elastic modulus, hardness and toughness of the as-cast and annealed glasses. These were complemented with detailed structural investigations using X-ray diffraction, microscopy (optical, scanning electron and high resolution transmission electron microscopies) and nuclear magnetic resonance spectroscopy. These investigations reveal a smooth variation of the mechanical properties with composition except for the composition corresponding to x=20. This deviation has been attributed to subtle changes in the glass structure due to amorphous phase-separation and heat-treatment-assisted nano-crystallization.