Superprotonic Transitions

Electrons are the charge carriers in most electronic transactions. Sometimes, in semiconductors, holes, the moving voids recently vacated by an electron, constitute a usable current flow.

But positive ions can also act as an important current. Lead-acid batteries in cars are a prominent application of this principle.

A particularly interesting phenomenon in this regard is the “superprotonic” transition, an effect discovered in the 1980s by Russian scientists, in which the proton conductivity jumps by several orders of magnitude at a certain temperature, when a structural rearrangement of some of the molecular oxyamion groups (such as SO₄) occurs.

Sossina M. Haile and her colleagues at Caltech (smhaile@caltech.edu, 626-395-2958) have performed new experiments which have expanded the roster of superprotonic materials, or cleared up past mysteries. For example, they have cleared up any doubt that the solid-form acid CsH₂PO₄, whose chemistry and conducting properties are especially promising as a candidate for the electrolyte in fuel cells, can undergo the superprotonic transition.

The new results were reported at last month’s meeting of the American Crystallographic Association in Chicago (also see Caltech website).