Quasi-periodic Crystals are unique in their atomic structure, a fact that intrigued an enthusiastic scientific community since 1984.  In addition to the determination of precise atomic positions in QCs, a challenging task by itself, the nature of defects and interfaces has also been researched.  New materials with QC structures have been discovered in unrelated metallic systems, and structures, which in the pre-QC era were labeled “complex”, are now well defined.  In addition, as new materials and large QC single crystals became available, there has been a dedicated ongoing effort to determine the physical properties of QC. These properties depend only partially on the atomic structure, and other factors may be just as important.  Thus the physical properties of QC in many cases resembles these of periodic intermetallics. However, in several cases, the physical properties of QC were found to be unique, and thus carry the promise of commercial applications.

This colloquium will detail the experiments that led to the discovery of quasi-periodic materials, and outline several  practical applications of their unusual properties.