Structural Studies of Technetium and Rhenium Oxides*

The oxide chemistry of technetium$-99$ (t$1/2 = 2.12\times~10^{5}$ y) has not been investigated to any significant extent and presents an opportunity to explore new structural, electronic and magnetic regimes. The chemistry of rhenium broadly resembles that of technetium, and although ReO$_{3}$ is a widely studied material with a prototypic structure, it exhibits an unusual thermal expansion evolution that we have studied using neutron powder diffraction. The results of the thermal expansion study will be presented. The structural study of TcO$_{2}$ and of a new ternary oxide containing technetium and bismuth Bi$_{2}$Tc$_{2}$O$_{7}$ will be also presented and discussed. Some new reactions of TcO$_{2}$ and other oxides of heavy elements will be described.