Nonlocal protons and deuterons opposed to disorder: a single-crystal neutron diffraction study of KH0.76D0.24CO3 and a theoretical framewok

Abstract

We show with neutron diffraction that a single-crystal of potassium hydrogen deuterium carbonate at room temperature, namely KH${}_{0.76}$D${}_{0.24}$CO${}_3$, is isomorphous with the KHCO${}_3$ and KDCO${}_3$ derivatives. Protons and deuterons are not disordered particles located at definite sites and Bragg peaks are best fitted with separate H and D sublattices. We propose a theoretical framework for nonlocal observables and macroscopic states compatible with the crystal field.