Structural perfection and residual resistivity of tungsten single crystals

A study was done of the residual resistivity ratio (RRR) and structural perfection of 99.98 wt % and 99.9995 wt % pure tungsten single crystals grown by the electron-beam floating zone method on seeds of (100), (110), (111), and (112) orientations. The RRR was found to depend on the crystallographic orientation of the growth axis of single crystals and to correlate with their structural perfection. The RRR of tungsten single crystals differing in purity showed a behavior that varied with their orientation. The correlation hetween the RRR and structural perfection of crystals is shown to be mainly determined by the scattering of conduction electrons at the boundaries of single-crystal substructural blocks (the internal size effect).