E. Karabudak; "Superprotonic phase.."

Superprotonic phase transition

in Cs_xRb_y H(PO3) solutions

Engin Karabudak

Summer Undergraduate Research Fellowship

California Institute of Technolgy

2002

Abstract:

A superprotonic phase transition is a structural transformation in a crystalline material at which the protonic conductivity increases by several orders of magnitute. Understanding these transitions and those compounds that undergo superprotonic phase transition may help develop a successful electrolyte for AUTOMATIVE FUEL cell. CsH(PO₃H) is known to have a superprotonic phase transition at 137^o C with a large heat of transformation, ∆H = 58 J / g.

RbH(PO₃H) is isostructural to CsHPO₃H but does not exhibit superprotonic behavior.

Large cation radii facilitate superprotonic phase transitions. The goal of this work is to synthesize the solid solution series Cs_xRb_1-xH(PO₃) and determine the minimum effective cation radius for which a superprotonic phase transition is not precluded.

Samples have been obtained from aqueous crystal growth. Thermal, microprobe analysis and powder x-ray diffraction have been performed on selected samples. The complete solid solution series is obtainable and preliminary results indicate that minimum effective cation radius for which a superprotonic pahse transition occurs in the MHPO₃H

system, is approximately 1.71 A which correspond to M = Cs_.25Rb_.75

January 7, 2005, 13:30, L047