Hard Science from Hard Materials
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Letter from the President
Hard Science from Hard Materials Okay, it’s time for a break from politics, funding, visas, and “issues” in general. This letter is about science, all science, nothing but science. I would like to take the opportunity to simply call attention to four recent, remarkable papers. They have only two things in common. First, they came to my attention through random browsing during a single three-hour Amtrak ride (as opposed to a literature search). Second, they report dramatic observations and achievements on prototypical, almost old-fashioned materials. With all the attention devoted lately to fancy “bio” materials and infinitesimal “nano” objects, I found it refreshing to read of major advances in some of the bread-and-butter materials of our field. The first article1 describes the activity of a finely dispersed silicate clay in controlling the phase and enhancing the mechanical strength of poly(vinylidene fluoride). This polymer is useful both for bulk engineering applications and also as a piezo/pyroelectric. When the clay is in the form of small enough platelets, it induces a preference for the otherwise less stable β phase of the polymer at the expense of the α phase, and simultaneously produces order-of-magnitude increases in toughness, with stiffness also increasing, a very unusual occurrence. The role of the clay is as much to change the domain structure and energy dissipation mechanism of the polymer as it is to add a theoretically “less deformable” component. While most of the paper deals with the properties of the polymer, it struck me that such profound effects were due to a “lowly” clay. The next article2 concerns strontium titanate (SrTiO3). Mobile charge carriers can be introduced into this material through the omission of some of the oxygen from the ideal stoichiometric formula. The oxygen vacancies act as dopants, much as do impurity atoms in semiconducting silicon. The amazing thing about the present study is not the nonstoichiometric composition, but rather the atomicscale definition of the position of the vacancies and, furthermore, the ability to image these vacancies with a resolution of just a few unit cells in the interior of the sample. The imaging depends on observing strain fields that distort adjacent cation sites. Fascinating and techno-
“I found it refreshing to read of major advances in some of the bread-and-butter materials of our field.”
logically relevant questions can be addressed with this newly available capability: How far do vacancies migrate, to what extent do they associate, and what are the thermodynamic limits to their distributional possibilities? It is difficult enough to find individual heavy atoms on a surface; here, the observation is that of missing light atoms in the bulk. We thus come closer to defining oxide physics with the precision of conventional semiconductor physics. The third article3 reports the realization of a holy grail in the field of oxide glasses. Aluminum oxide, certainly an ancient material, has long been attractive as a po
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