Unusual Indentation Behavior of Alkali Metaphosphate Glass Above Glass Transition Temperature

Abstract

The mixed alkali metaphosphate glass 12.5Li2O–12.5Na2O–12.5K2O–12.5Cs2O–50P2O5 (mol%) compressed under uniaxial stress shows unusually large recovery of its shape during heating above its glass transition temperature (Tg). To clarify the mechanism, the viscous, elastic, and plastic behavior of the metaphosphate glass was investigated with the depth‐sensing indentation method. From the load‐displacement (P–h) curves of the glass, a large recovery of the depth displacement was found during unloading above Tg. By analyzing the P–h curves with a viscous–elastic–plastic model, the large recovery was concluded to be due to larger elastic deformation than viscous deformation even above Tg. The phenomenon can be attributed to relaxation to the randomly oriented ‐P–O–P– chain structure from the oriented chain structure formed under stress in the metaphosphate glass.