Influence of Boron Oxide on the Physicomechanical Properties of Glasses in the Li2O–B2O3–P2O5 System

The mechanical properties of glasses in the Li2O–B2O3–P2O5 system are investigated as a function of the boron oxide content in the range from 5 to 30 mol % at a constant lithium oxide content of 45 mol %. It is demonstrated that, as the B2O3 content increases, the density of glasses passes through a maximum at 20 mol % B2O3 and the molar volume decreases gradually. The elastic modulus and the hardness of glasses monotonically increase with an increase in the B2O3 content. An increase in the B2O3 content leads to a decrease in the structural strength (measured using the method of three-point bending of fibers) and the fracture toughness (determined by the microindentation technique). The assumption is made that the decrease in the strength characteristics is caused by the phase separation developed in the structure of lithium phosphate glass with an increase in the B2O3 content.