Hydrogen ordering pattern of K₃D(SO₄)₂ in low temperature phase

Abstract

K₃D(SO₄)₂ undergoes a phase transition at T_c = 85 K associated with cell doubling (ax2bx2c) with decreasing temperature. Structure analysis of K₃D(SO₄)₂ was performed by X-ray diffraction experiments at 20 K in order to investigate the structure of the low temperature phase. The excess electrons in the hydrogen-bond were studied by differential fourier synthesis. The excess electrons at room temperature were symmetrically double peaks along the hydrogen-bond while they changed to become asymmetrical along the hydrogen-bond. If we define a dipole moment induced by the deuteron shift patterns in the unit cell, the sum of the dipole moment is almost zero in a larger unit cell, which is consistent with the mode condensation model at the zone boundary point in a reciprocal cell.

Key Words:

• Isolated hydrogen-bonded system
• K₃D(SO₄)₂
• X-ray structure analysis
• hydrogen ordering pattern