Defect structure and its nomenclature for mixed conducting lanthanum tungstates La28–xW4+xO54+3x/2

Based on results from experimental and theoretical studies of the crystal structure of lanthanum tungstate (La28−xW4+xO54+32xv2−32x), we present a defect model comprising an inherently disordered and partially occupied oxide ion sublattice, which rationalizes hydration and ionic conduction of the materials in the undoped state. Applying the model to experimental conductivity data enables extraction of defect thermodynamics and transport parameters of protons, oxide ions and electronic defects. The standard enthalpy and entropy changes of the hydration of inherent oxygen vacancies are estimated to be −83 kJ/mol and −125 J/mol K (per mole of H2O), respectively.

► We present a new defect model of mixed conductor LWO53–LWO57.
► Defect structure is based on inherent disorder and partial occupancy.
► Defect structure rationalizes hydration in the undoped state.
► We extract thermodynamics of hydration by fitting to conductivity data.