phenomena in materials in the last 20 years. Although we may have missed some important discoveries, the trends discussed here are accurate. Having examined the key elements in a discovery and where and how it took place, we looked for recent changes in these patterns that may portend further change. The following summary is in two parts, the first of which deals with bulk materials, and the second with artificially structured materials.

BULK MATERIALS

The table on page 163 lists some materials in which new phenomena have been discovered or in which a particular property has been considerably enhanced in the last decade or two. Also included are some materials in thin-film form. These can also be prepared in bulk form, but their usefulness arises from the ability to make films or wires (e.g., NbN and Nb3Sn). Since the compounds are stable in bulk form, they are included here. It is immediately evident from this table that the new compounds—that is, their composition and crystal structure—were often discovered by one group, usually not in the United States, and that the new phenomena were discovered by another group, most often in the United States. In a few cases the compounds were discovered as a result of seeking the particular property (e.g., Fe14Nd2B or RbAg4I5). In some cases the structure type has been known for a long time, but the particular compound had never been examined in a way that revealed something new. In those cases the table shows the structure type rather than a reference to its discovery. The discovery of metal insulator transitions in 1946 did not trigger immediate worldwide interest; rather, that field blossomed in the mid-1950s and again in the late 1960s, and important advances are continuing today.

The organization of the table is somewhat misleading in the following ways. First, the understanding and the synthesis method to discover particular materials have most often been developed in programs that produced materials with rather ordinary properties.

Second, by focusing on properties, we ignore the most common motivations for the original synthesis, which are usually to develop a new chemistry, or to make materials with new or unusual structures, or to elucidate reaction mechanisms particularly when new preparative conditions or techniques are discovered. The purpose for such studies is usually to understand the relation between chemical bonding and crystal structure. Indeed, many of the compounds listed in the table were discovered by “accident” rather than by design, while researchers were examining the phases that result from new combinations of elements. These searches were often empirical, motivated by the expectation that new structures would result, the exact nature of which was not certain. Since there is as much art as science in the consistent discovery of new materials, the scientists who most frequently find new



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