size are all factors which strongly influence the metastable retention of the HPZ phase of zirconia. Discrepancies reported earlier on the P-T phase diagram of ZrOz based on results obtained from retrieved products'" can be explained by the relevant effects mentioned above.(2) The results obtained here support the idea that the transformation involving the monoclinic and HPZ phases in zirconia is initiated at nucleation centers whose potency can be minimized by appropriate annealing thermal treatments.(3) Finally, the results point out the importance of high pressure as a source of controllable driving force to induce the martensitic-type transformation, thus permitting the use of thermal annealing treatments as a means of solely changing the population of defects involved in nucleating the transition. A more systematic and quantitative study of these defects is necessary, mainly to uncover the precise nature of the defects acting as nucleation centers as well as to understand similar effects in other systems.

A cover glass that is capable of having a deep ion exchange compression layer enables one to tailor the glass to the intended device application. Key to this effort is having a glass mechanics framework that includes resistance to visible and strength‐limiting contact damage as well as maintaining sufficient strength to survive localized glass flexing during contact events.

As optical fiber penetrates further into the communications infrastructure and comes closer to the home or business, higher optical power levels are expected. Several studies have shown that sharply bent optical fiber will fail prematurely when exposed to high optical power levels. In an extreme case, where the fiber is bent to a maximum bend stress on the order of 2 GPa and subjected to a power level of 1–2 W in the near‐infrared wavelength window, optical fiber will fail in minutes. Time to failure decreases with increasing bend stress and optical power. A recent report suggests that power levels in the range of a few hundred milliwatts may be enough to induce delayed failure in bent fiber. This study explores the progression of events leading to failure. Light that escapes the core of bent fiber passes into the coating, where a small amount is absorbed and converted to heat. The coating heats to a stable temperature and visually darkens with time. This is followed by an abrupt rise in temperature, which occurs as the coating transforms to a highly absorptive material, consistent with thermal runaway. The abrupt rise in coating temperature stimulates viscoelastic deformation of the glass. Glass deformation is explained in terms of the ability of highly quenched glass to experience viscous flow at temperatures well below the glass transition range (i.e. sub‐Tg aging or relaxation). As the glass portion of the fiber moves toward a “kinked” configuration, it concentrates more power on a smaller region of coating, resulting in further temperature increase. There is no evidence of the fiber fuse effect in the lower viscosity glass core. The final kinked configuration of the glass fiber leads to complete attenuation of the light and failure is complete. Coating decomposition is self‐limiting with no visible flame. A coating with a refractive index near or below that of silica was found to virtually eliminate this failure mode.

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