Structure and electrical properties of the new pyrochlore-type protonic solid electrolyte K(0.88)Nb2O(7.58)H(4.28).

Single-crystal, synchrotron powder X-ray diffraction and neutron powder diffraction studies of the novel pyrochlore-type compound with the structural formula K(0.88)(OH)(0.54)H(1.66)(H(2)O)(1.04)Nb(2)O(6) suggests that the water molecules are located in 32e sites, and the hydroxide ions and potassium ions are located in 16d sites with a significant amount of 'free' protons in 96g sites. The total weight loss at temperatures up to 773 K is only about 8%, suggesting the oxygen escape from 48f sites can be excluded and 'free' protons must be preserved in the structure. The bulk conductivity in ambient air reaches 10(-2) S cm(-1) at 623 K. Owing to the extended stability range and resistance to water solubility, the compound can be considered as a candidate for intermediate temperature solid-oxide fuel-cell applications.