Nuclear qadrupole resonance study of the molecular dynamics in KH2AsO4 under high hydrostatic pressure

Potassium dihydrogen arsenate (KDA) belongs to the highly relevant group of hydrogen bonded ferroelectrics the properties of which are the subject of intense study, both theoretically and experimentally. KDA crystal consists of tetrahedral AsO4 groups, connected by O-H...O bonds. The proton dynamics in the bonds plays an essential role in the description of the phenomena occurring in these crystals. We have used NQR spectroscopy for the determination of the influence of pressure on the molecular dynamics in KH2AsO4. Using the disappearance of NQR frequency in the Curie temperature as a monitor of the phase transition, we elucidated the Curie point versus pressure dependence, determined the change in crystal volume in the transition and laid stress on the essential role of the hydrogen bonds in the dynamical properties of the crystal. (author)