Structural, thermal and electrical studies of a novel rubidium phosphite tellurate compound (original) (raw)

Abstract

Structural, thermal and electrical properties studies of rubidium phosphite tellurate, RbH(PO 3 H)ÁTe(OH) 6 , were performed. An endothermic peak, which reached a completion at about 315 8C accompanied with a weight loss of 4.6 wt.%, was attributed to dehydration. Four types of pellets were produced, namely pellets A, B, C and D. Pellet A was tested with platinum-carbon paper electrode, and pellets B, C and D were tested with gold electrodes. Both pellets A and B were studied from 113 8C to 317 8C for 135 h. Pellet C was first investigated from room temperature to 176 8C for 360 h. After cooling down to room temperature, a second measurement with pellet C was carried out under the same conditions as used for pellets A and B. Pellet D, on the other hand, was heated up to 450 8C, kept at that temperature for 2 h and then cooled down to room temperature prior to the conductivity measurements. It was observed that the conductivities of pellets A and B decreased to values of 5.2 Â 10 À8 S cm À1 and 6.6 Â 10 À7 S cm À1 at 317 8C, respectively, and an unexpected rise in the conductivity (9.89 Â 10 À6 S cm À1 at 317 8C) was seen with pellet C. Dehydration of RbH(PO 3 H)ÁTe(OH) 6 might be responsible for this unexpected rise in the conductivity of pellet C. The monoprotic part RbH(PO 3 H) of RbH(PO 3 H)ÁTe(OH) 6 apparently became diprotic (Rb 2 H 2 P 2 O 5) part of Rb 2 H 2 P 2 O 5 Á[Te(OH) 6 ] 2 after dehydration. The measured conductivity of pellet D, which was dehydrated prior to the measurement, reached a value of 5.41 Â 10 À5 S cm À1 at 317 8C and showed a good stability over-each-run time and temperatures measurement up to 317 8C. The dehydrated compound, Rb 2 H 2 P 2 O 5 Á[Te(OH) 6 ] 2 , has also a higher hydrogen density relative to the starting compound, RbH(PO 3 H)ÁTe(OH) 6. It is deduced that completion of the dehydration can be responsible for the unexpected rise in the conductivity of RbH(PO 3 H)ÁTe(OH) 6. This unusual case is important for studies in solid acid proton conductors.

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