Pressure Effect on Phase Transition in Partially Deuterated Rb(H_1-xD_x)₂PO₄

Abstract

Measurement of the dielectric constant along the polar axis for tetragonal and monoclinic Rb(H_1-x D _x )₂PO₄ crystals was carried out under the hydrostatic pressure using by an LCR mater. The values of the pressure derivative of the transition temperature, dT _C/dp, hardly depend on the deuterium concentration for the monoclinic Rb(H_1-x D _x )₂PO₄ crystal. In the tetragonal crystals, the values of dT _C/dp are −87 K/GPa for the tetragonal RbH₂PO₄ crystal and −38 K/GPa for the crystal with x = 0.74. The absolute value of dT _C/dp for tetragonal RbH₂PO₄ decreases extremely on deuteration. The deuteration effect on dT _C/dp in tetragonal RbH₂PO₄ crystals is large, though it is hardly observed in monoclinic RbH₂PO₄ crystals.

Keywords:

• RbH₂PO₄
• phase transition
• pressure effect
• dielectric constant
• isotope effect