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  New Li -Mg phosphates with 3D framework : experiment and ab initio calculations

Kellerman, D. G., Tyutyunnik, A. P., Medvedeva, N. I., Chufarov, A. Y., Fortes, A. D., Gibbs, A., et al. (2020). New Li -Mg phosphates with 3D framework: experiment and ab initio calculations. Dalton Transactions, -. doi:10.1039/D0DT01963A.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-AA9C-B Version Permalink: http://hdl.handle.net/21.11116/0000-0006-AA9D-A
Genre: Journal Article

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Kellerman, Dina Georgievna, Author
Tyutyunnik, Alexander P., Author
Medvedeva, Nadezhda Ivanovna, Author
Chufarov, Aleksandr Yu., Author
Fortes, Andrew Dominic, Author
Gibbs, Alexandra, Author
Tarakina, Nadezda V.1, Author              
Kalinkin, Mikhael, Author
Zhuravlev, Nickolai, Author
Leonidova, Olga, Author
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1Nadezda V. Tarakina, Kolloidchemie, Max Planck Institute of Colloids and Interfaces, Max Planck Society, ou_2522693              

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 Abstract: Two new lithium-magnesium phosphates LiMg6(PO4)3(P2O7) and Li(Mg5.62Sc0.19Li0.19)(PO4)3(P2O7) were synthesized by the solid-phase method. Using high-resolution time-of-flight neutron powder diffraction (TOF NPD) and X-ray powder diffraction (XRPD), we established that these phosphates have Pnma orthorhombic structure with the cell parameters a=9.14664(5) Å, b=18.83773(8) Å, c=8.27450(4) Å, V=1425.71(1) Å3 and a=9.14516(5) Å, b=18.84222(9) Å, c= 8.28204(4) Å, V=1427.12(1) Å3, respectively. The crystal structures can be described by stacking of the [Mg6O18] or [Mg5.62Sc0.19Li0.19O18] wavy layers, which are parallel to the (100) direction and interconnected through PO4 tetrahedra and P2O7 groups to a 3D-framework. Li atoms are located in large tunnels formed in a 3D lattice, which contributes to lithium diffusion. AC impedance spectroscopy shows that LiMg6(PO4)3(P2O7) and Li(Mg5.62Sc0.19Li0.19)(PO4)3(P2O7) have Li ion conductivity of 3.6 10-4 S/cm and 1.7 10-4 S/cm at 950 °C, with activation energy of 1.28 eV and 1.55 eV, respectively. NMR MAS studies confirmed a coexistence of pyro- and orthogroups in the structure of both phases and two lithium positions in Li(Mg5.62Sc0.19Li0.19)(PO4)3(P2O7). The first- principles method was used to study the electronic structure and stability of the two phases. The calculated formation enthalpies demonstrated that Sc is a stabilizing impurity in LiMg6(PO4)3(P2O7), while there exists a strong destabilization of olivine LiMgPO4 upon doping with Sc. This explains the failure to synthesize the Sc-doped olivine. The new phosphate LiMg6(PO4)3(P2O7) is a dielectric with band gap of 5.35 eV, which decreases to 4.85 eV due to a localized Sc 3d peak upon doping with Sc. These findings are consistent with the results obtained from UV-Vis spectroscopy. The new phase may be a good optical matrix similar to LiMgPO4.

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Language(s): eng - English
 Dates: 2020-06-30
 Publication Status: Published online
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 Rev. Method: -
 Identifiers: DOI: 10.1039/D0DT01963A
BibTex Citekey: D0DT01963A
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Title: Dalton Transactions
  Abbreviation : Dalton Trans.
Source Genre: Journal
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Publ. Info: Cambridge, UK : Royal Society of Chemistry
Pages: - Volume / Issue: - Sequence Number: - Start / End Page: - Identifier: ISSN: 1477-9226