Neutron scattering and diffraction investigations of proton glass state in system (K,NH₄)H₂PO₄

A.V. Beluskin (Frank Laboratory of Neutron Physics, JINR, 141980 Dubna, Russia) and L.A. Shuvalov (Institute of Crystallography, 117333 Moscow, Russia)

The results of neutron diffraction, inelastic and quasielastic neutron scattering studies on mixed crystals K_1-x(NH₄)_xH₂PO₄ will be presented. The anomalous behaviour of the proton glass system which is formed for ammonium concentration 0.2<x<0.8 is compared with the relevant properties parent ferroelectric KH₂PO₄ and antiferroelectric NH₄H₂PO₄ crystals. The following effects to be discussed:
a) influence of the proton glass transition on crystal structure;
b) the effect of random bonds and random fields on proton dynamics;
c) anomalous increase of mean square displacements of protons in hydrogen in the glass phase;
d) gradual freezing of the rotational dynamics of ammonium ions in the paraelectric phase of the glass composition samples and an order parameter of NH₄ groups.
The results of present studies will be compared with the data obtained by experimental techniques: dielectric susceptibility, NMR, EPR, X-ray diffraction, optical spectroscopy.