Volume-corrected isomer shifts of transition-metal impurities: An orbital electronegativity scale

It is shown that, once volume effects are accounted for, a universal curve describes the M\"ossbauer isomer shifts of ⁵⁷Fe, ⁹⁹Ru, ¹⁸¹Ta, ¹⁹³Ir, ¹⁹⁵Pt, and ¹⁹⁷Au impurity nuclei in a variety of hosts. The curve defines an "orbital" electronegativity associated with non-d electron charge flow on or off these transition-metal atoms in alloys. The shape of the curve is remarkable in the extent to which it agrees with the "total" electronegativity scales of Pauling, Gordy-Thomas, and others. This agreement suggests that d and non-d charge flow are simply proportional to one another to an extent we find surprising.