We show with neutron diffraction that a single-crystal of potassium hydrogen
deuterium carbonate at room temperature, namely KH0.76D0.24CO3, is
isomorphous with the KHCO3 and KDCO3 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