Publications by authors named "Pascale Armand"

3 Publications

  • Page 1 of 1

Structural and Vibrational Study of CsSbGeO, a New Germanate in the SbGeO Family ( = Alkali Metal).

Inorg Chem 2021 Jul 30;60(14):10361-10370. Epub 2021 Jun 30.

ICGM, Université Montpellier, CNRS, ENSCM, Montpellier 34095, France.

The germanate CsSbGeO, grown spontaneously via the high-temperature solution method from CsMoO used as a flux, crystallizes in the orthorhombic system with = 12.3636(2), = 13.8521(2), = 31.4824(5) Å, and = 5391.73(2) Å. Its structure, determined from single-crystal X-ray diffraction data, is most probably noncentrosymmetric despite our choice to report it in the centrosymmetric maximal supergroup (no. 62) in which agreement factors 1 0.0371 and w2 = 0.0706 (all data) were obtained. The unit cell contains 24 formulas CsSbGeO. The three-dimensional network is built up with regular germanate tetrahedra at nine crystallographically independent Ge sites. The Sb atoms (four independent positions) adopt octahedral coordination with O atoms, and the Cs cations are located in the channels of the 3-D network. A more in-depth analysis of the structure of CsSbGeO is carried out in the light of the structures previously determined for the compounds SbGeO ( = K, Rb) having the same chemical formula but significantly different atomic arrangements. The structural characteristics are discussed related to literature and the nature of the monovalent cation .
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http://dx.doi.org/10.1021/acs.inorgchem.1c00747DOI Listing
July 2021

High-temperature elastic moduli of flux-grown α-GeO2 single crystal.

Chemphyschem 2014 Jan 2;15(1):118-25. Epub 2013 Dec 2.

Institut Charles Gerhardt Montpellier, UMR 5253, CNRS-UM2-ENSCM-UM1, C2M, Université Montpellier 2, CC 1504, Place Eugène Bataillon, 34095 Montpellier Cédex 5 (France), Fax: (+33) 467144290.

From high-precision Brillouin spectroscopy measurements, six elastic constants (C11, C33, C44, C66, C12, and C14) of a flux-grown GeO2 single crystal with the α-quartz-like structure are obtained in the 298-1273 K temperature range. High-temperature powder X-ray diffraction data is collected to determine the temperature dependence of the lattice parameters and the volume thermal expansion coefficients. The temperature dependence of the mass density, ρ, is evaluated and used to estimate the thermal dependence of its refractive indices (ordinary and extraordinary), according to the Lorentz-Lorenz equation. The extraction of the ambient piezoelectric stress contribution, e11, from the C'11-C11 difference gives, for the piezoelectric strain coefficient d11 , a value of 5.7(2) pC N(-1), which is more than twice that of α-quartz. As the quartz structure of α-GeO2 remains stable until melting, piezoelectric activity is observed until 1273 K.
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http://dx.doi.org/10.1002/cphc.201300793DOI Listing
January 2014

Vibrational origin of the thermal stability in the highly distorted α-quartz-type material GeO2: an experimental and theoretical study.

Inorg Chem 2013 Jun 4;52(12):7271-9. Epub 2013 Jun 4.

Institut Charles Gerhardt Montpellier (ICGM), UMR 5253 CNRS-UM2-ENSCM-UM1, équipe C2M, Université Montpellier II, Place Eugène Bataillon, 34095 Montpellier cedex 5, France.

We report an experimental and theoretical vibrational study of the high-performance piezoelectric GeO2 material. Polarized and variable-temperature Raman spectroscopic measurements on high-quality, water-free, flux-grown α-quartz GeO2 single crystals combined with state-of-the-art first-principles calculations allow the controversies on the mode symmetry assignment to be solved, the nature of the vibrations to be described in detail, and the origin of the high thermal stability of this material to be explained. The low-degree of dynamic disorder at high-temperature, which makes α-GeO2 one of the most promising piezoelectric materials for extreme temperature applications, is found to originate from the absence of a libration mode of the GeO4 tetrahedra.
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http://dx.doi.org/10.1021/ic4009416DOI Listing
June 2013