“Free” Volume Expansion and Formation Enthalpy of Defects as Key Parameters Tuning the Oxide Ionic Conductivity in Derivatives of β-La2Mo2O9

• Published in: Chemistry of Materials
• Main Authors: Corbel, Gwenaël, Selmi, Ania, Suard, Emmanuelle, Lacorre, Philippe
• Other Authors: Institut des Molécules et Matériaux du Mans (Le Mans), Institut Laue-Langevin (ILL)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2014
• Subjects: Neutron powder diffraction; Free volume expansion; Oxide ion conduction; Frenkel defects; Dienes-Macedo-Litovitz equation; Vogel-Tammann-Fulcher equation; LAMOX; [CHIM.MATE]Chemical Sciences/Material chemistry; [CHIM.CRIS]Chemical Sciences/Cristallography; [CHIM.INOR]Chemical Sciences/Inorganic chemistry; DML
• Online Access: https://hal-univ-lemans.archives-ouvertes.fr/hal-01952292; https://hal-univ-lemans.archives-ouvertes.fr/hal-01952292/document; https://hal-univ-lemans.archives-ouvertes.fr/hal-01952292/file/Manuscript_Corbel_DML%20structure-conductivity%20relationship%20in%20LAMOX_2014.pdf; https://doi.org/10.1021/cm503461x

International audience The crystal structure of fast oxide-ion conductor β-La1.85Ba0.15Mo2O8.925 and its thermal evolution have been studied using neutron powder diffraction, and compared to those already published [G. Corbel et al., Chem. Mater. 2011, 23, 1288] of a bismuth counterpart in the LAMOX family, β-La1.7Bi0.3Mo2O9. Comparable evolutions have a tendency to suggest that the observed behavior, a specific combination of rotation and distortion of cationic building units, is a common feature of La-substituted β-LAMOX compounds. For the first time in crystallized solids, a quantitative link is made for both compounds between the high-temperature (high-T) conductivity increase relative to Arrheniusbehavior and the volume expansion of the voids, through consecutive fits to crystallographic and conductivity data of the Dienes−Macedo−Litovitz (DML) equation. Both the expansion of the “free” volume (VF) and the formation enthalpy of the Frenkel defects (ΔHf) are the key parameters tuning the conductivity of LAMOX compounds above T0 = 400−450 °C. A substitution strategy of La in La2Mo2O9 is proposed in order to optimize anionic conductivity, based on crystallographic grounds.