Synthesis and structure of anisotropic borosilicate glasses under differential stress at high pressure and temperature

Abstract Deformation experiments were performed on borosilicate glasses, 20Na 2 O‐50B 2 O 3 ‐30SiO 2 (labeled 253NBS) and 10Na 2 O‐80B 2 O 3 ‐10SiO 2 (labeled 181NBS), under confining pressure condition at sub‐ T g conditions. Anisotropy in the glass decreased as the temperature approached T g due to the enhanced mobility of the glass structure. The 181NBS, which has a highly polymerized network mainly consisting of three‐coordinated boron (B III ), exhibited a high birefringence value comparable to that of quartz. Boron K‐edge XANES suggests that B III is oriented perpendicular to the principal stress direction. Furthermore, high‐energy X‐ray total scattering analysis indicated a layer‐like structure composed of B III interconnected by tetrahedral units, SiO 4 and/or BO 4 .