Neutron diffraction study of the monoclinic to tetragonal structural transition in LaNbO4 and its relation to proton mobility

• The fergusonite-scheelite structural transition of LaNbO4 was characterized by high-intensity variable temperature neutron powder diffraction in an effort to link structural changes to proton transport in the low temperature monoclinic and high temperature tetragonal polymorphs. The pronounced decrease in enthalpy of proton mobility with increasing temperature in monoclinic LaNbO4, identified by Field et al. [1], was found to coincide with the decrease in a key inter-tetrahedral oxygen separation. At temperatures above the transition, this oxygen to oxygen distance remains constant, behavior that is consistent with the invariant nature of the calculated enthalpy of mobility for the tetragonal phase. This oxygen separation is therefore proposed as the key structural parameter determining the success rate of proton transfer and ultimately the proton diffusion in LaNbO4. Infrared measurements performed on acceptor-doped LaNbO4 show an absorption in the region 2500 to 3700 cm(-1) attributed to the O-H stretching motion influenced by hydrogen bonding.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

Proton conductors

Neutron diffraction

Structural phase transition

Fuel cell electrolytes

rare-earth orthoniobate

phase-transitions

domain boundary

oxides

conduction

transformation

solubility

niobates

conduction

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)