An ionic conductor resembles a crowded bus where passengers (ions) try to squeeze toward the exit. Previously, it was thought that fast exit could be achieved either by a gently swaying bus (soft lattice) or by passengers standing in chaotic order (geometric disorder). The new work shows these are not two different tricks but the same one. The bus swaying and passenger jostling are parts of a single mechanism.
The authors took a mathematical model where ions and lattice atoms interact and eliminated the fast motion of the atoms themselves. The result is a correction to the energy that depends on how the forces between ions project onto the lattice stiffness. In simplified form, this correction splits into two parts: a local "sticking" of the ion to its site and a nonlocal influence of some ions on others through deformation of the entire lattice. Together, they reshape the energy landscape, as if the elevation map for passengers suddenly changed because the bus floor slightly sagged.
Calculations for two real materials — cubic lithium lanthanum zirconium oxide (Li7La3Zr2O12) and silver chromium selenide (AgCrSe2)—confirmed the picture. In both cases, the included correction lowered energy barriers and made ions move more coherently, in groups. It turned out that softness, disorder, and collective motion are not separate phenomena but three projections of the same reshaped landscape.
Such a unified view changes the approach to finding new conductors. Instead of separately selecting a soft material and separately a suitable disorder, one can look for substances where the crystal structure itself naturally creates both effects. It is like designing a bus where the floor is specially springy, helping passengers exit faster.
In cubic Li7La3Zr2O12, lithium ions can jump between neighboring sites up to a billion times per second at room temperature — about as fast as a mosquito's wings beat in flight.
In Peter Watts's novel Blindsight, aliens use solid superconductors with tunable internal structures — much like the materials with "reshaped" energy landscapes described here.