Structural, thermal and electrical studies of a novel rubidium phosphite tellurate compound

Structural, thermal and electrical properties studies of rubidium phosphite tellurate, RbH(PO 3 H)·Te(OH) 6 , were performed. An endothermic peak, which reached a completion at about 315 °C 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 °C to 317 °C for 135 h. Pellet C was first investigated from room temperature to 176 °C 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 °C, 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 × 10 −8 S cm −1 and 6.6 × 10 −7 S cm −1 at 317 °C, respectively, and an unexpected rise in the conductivity (9.89 × 10 −6 S cm −1 at 317 °C) was seen with pellet C. Dehydration of RbH(PO 3 H)·Te(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)·Te(OH) 6 apparently became diprotic (Rb 2 H 2 P 2 O 5 ) part of Rb 2 H 2 P 2 O 5 ·[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 × 10 −5 S cm −1 at 317 °C and showed a good stability over-each-run time and temperatures measurement up to 317 °C. The dehydrated compound, Rb 2 H 2 P 2 O 5 ·[Te(OH) 6 ] 2 , has also a higher hydrogen density relative to the starting compound, RbH(PO 3 H)·Te(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)·Te(OH) 6 . This unusual case is important for studies in solid acid proton conductors.