It is well known that lattice parameters of most alloyed solids can be interpolated almost linearly with the composition between those of the two end-members. This, confirmed within a reasonable degree of accuracy by a huge body of structural investigations over many decades using the x-ray diffraction technique, is the celebrated Vegard's Law. In fact, many properties, such as the bandgap of an alloyed semiconductor, are also known to show a similar linear behaviour between the end-members with composition. These observations form the basis of the vast literature aimed at tuning of properties by making solid solutions. There is a closely associated concept of chemical pressure achieved by the substitution of typically a cation in a solid with another ion of dissimilar size defining a dilute alloy. This technique not only allows to exert a positive pressure by doping a smaller cation akin to the physical pressure, but also makes it feasible to explore of the negative pressure regime inaccessible otherwise with the help of a larger sized dopant. While these concepts are universally accepted and much used in designing new compounds with tailor-made properties, a closer, microscopic inspection reveals many surprises not fully appreciated in the past. Based on some of our recent studies, I shall illustrate the limits of these concepts and provide a rationale for their apparent success in spite of several conceptual difficulties.
D. D. Sarma (Indian Institute of Science, Bangalore)
Date & Time
13 February 2017, 15:00 to 16:00
Emmy Noether Seminar Room, ICTS Campus, Bangalore