New molybdo-sulfates and molybdo-phosphates of LAMOX type : transitions mechanisms and anionic conduction
type: Dataset
description: A new ionic conductor of the solid solutions La2Mo2-yPyO9-y/2 (y ? 0.05) and La2Mo2-ySyO9 (y ? 0.6) has been prepared with conventional solid-state reaction method. The resultant oxide powders were characterized by X-ray diffraction. These two series of lanthanum molybdates, which belong to the LAMOX family of fast oxide-ion conductors, exhibits a different structural behavior depending on the substituting element. The effect of substituting P for Mo reveals that the phase transition which occurs in La2Mo2O9 around 560°C disappears when y > 0.02. Substituting P in some degree (y > 0.02) for Mo6+ can suppress the phase transition and stabilizing the cubic phase of ?- La2Mo2O9. The sulfur series (up to around 30 %) suppress the phase transition which occurs in La2Mo2O9 around 580°C from a low temperature ? form to a high temperature ?, and stabilize the ? form at room temperature.Thermogravimetric analysis showed that the substitution of molybdenum by sulfur greatly decreased the thermal stability of phases making their characterization by X-ray diffraction and impedance spectroscopy difficult. For the series La2Mo2-yPyO9-y/2, a partial segregation of phosphorus was demonstrated by NMR spectroscopy. Electrical measurements performed on the two sets of samples showed significant conductivity, but still less than that observed at high temperature for the parent compound La2Mo2O9.The infrared and Raman spectra of the low- and high-temperature phases of LAMOX were performed at ambient temperature. All theoretically predicted vibrations have been observed, and assignments have been given for the internal vibrations of the MoO42-, SO42- and PO43- ions as for the external vibrations. It is interesting to study the vibrational spectra of these two phases (? and ?) in order to obtain more conclusive data regarding the internal vibrations of the XO4 (X= Mo, P, S).
identifier: NNT: 2012LEMA1015
issued: 2026-05-15T13:17:30.969697
language: fr
modified: 2026-05-15T13:17:30.969702
contact point: Organization
  fn: CCSD
keyword: calcul-ab-initio
keyword: chimothechemical-sciencesother
keyword: conducteurs-ioniques
keyword: infoeu-reposemanticsdoctoralthesis
keyword: infrared
keyword: la2mo2-ypyo9-y2
keyword: la2mo2-ysyo9
keyword: la2mo2o9
keyword: nmr-spectroscopy
keyword: oxide-ion-conductors
keyword: phase--et
keyword: phase-transition
keyword: raman
keyword: sofc
keyword: spectres-de-phonons
keyword: spectroscopie-raman
keyword: spectroscopie-rmn
keyword: theses
keyword: x-ray-diffraction
landing page: https://theses.hal.science/tel-00770659

New molybdo-sulfates and molybdo-phosphates of LAMOX type : transitions mechanisms and anionic conduction
type: Distribution
format: HTML
issued: 2026-05-15T13:17:30.976073
modified: 2026-05-15T13:17:30.905840
access URL: https://theses.hal.science/tel-00770659

test_moissonnage_selune
type: Agent