High-temperature transformation was studied by using impedance spectroscopy, differential thermal analysis, and thermogravimetry. Complex alternating-current impedance spectra revealed an impedance in 2 regions of measuring frequency. A low-frequency region was attributed to the formation and migration of H2O molecules at the surface. The conduction mechanism of a high-frequency region seemed to be of Cole-Cole type and was attributed to proton migration in the bulk. The results supported the suggestion that the phase above 230C was not a superionic conductor caused by a transition from monoclinic to cubic, but rather a polymeric state which was caused by partial thermal decomposition. A possible cause of proton conduction was suggested to be partial thermal decomposition of the crystal surface; because the polymeric transition tended to increase breakage and re-forming of H bonds at the surface.

Possible Origin of the Proton Conduction Mechanism of CsH2PO4 Crystals at High Temperatures. J.H.Park: Physical Review B, 2004, 69[5], 054104 (6pp)