Rb85, Rb87, and O17 nuclear-quadrupole-resonance study of Rb(H1−xDx)2PO4

Abstract

The Rb85, Rb87, and O17 nuclear-quadrupole-resonance frequencies and line shapes have been measured in RbH2PO4 and in Rb(H1−xDx)2PO4 (x=0.5,0.7) with the nuclear-quadrupole double-resonance technique. The results show that in the paraelectric phase the Rb+ ions move in a single-site potential, whereas the protons are dynamically disordered between two sites in the O-H...O hydrogen bonds. The ferroelectric phase transition in RbH2PO4 is associated with the freezing out of the proton motion in the O-H...O hydrogen bonds that induces a shift of the Rb+ ions along the ferroelectric axis. In the partially deuterated compounds the O-H...O hydrogen bonds are practically identical to the ones in pure RbH2PO4 and are thus only weakly influenced by the surrounding O-D...O bonds. The O-D...O bonds are, however, significantly more asymmetric and presumably longer than the O-H...O bonds.