Shoko, Elvis, Dang, Yun 
ORCID: 0000-0002-0140-0140, Han, Guopeng, Duff, Benjamin B ORCID: 0000-0002-7398-5002, Dyer, Matthew S ORCID: 0000-0002-4923-3003, Daniels, Luke M ORCID: 0000-0002-7077-6125, Chen, Ruiyong ORCID: 0000-0002-5340-248X, Blanc, Frederic ORCID: 0000-0001-9171-1454, Claridge, John B ORCID: 0000-0003-4849-6714 and Rosseinsky, Matthew J ORCID: 0000-0002-1910-2483
(2021)
Polymorph of LiAlP<sub>2</sub>O<sub>7</sub>: Combined Computational, Synthetic, Crystallographic, and Ionic Conductivity Study.
INORGANIC CHEMISTRY, 60 (18).
pp. 14083-14095.
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Abstract
We report a new polymorph of lithium aluminum pyrophosphate, LiAlP<sub>2</sub>O<sub>7</sub>, discovered through a computationally guided synthetic exploration of the Li-Mg-Al-P-O phase field. The new polymorph formed at 973 K, and the crystal structure, solved by single-crystal X-ray diffraction, adopts the orthorhombic space group <i>Cmcm</i> with <i>a</i> = 5.1140(9) Å, <i>b</i> = 8.2042(13) Å, <i>c</i> = 11.565(3) Å, and <i>V</i> = 485.22(17) Å<sup>3</sup>. It has a three-dimensional framework structure that is different from that found in other LiM<sup>III</sup>P<sub>2</sub>O<sub>7</sub> materials. It transforms to the known monoclinic form (space group <i>P</i>2<sub>1</sub>) above ∼1023 K. Density functional theory (DFT) calculations show that the new polymorph is the most stable low-temperature structure for this composition among the seven known structure types in the A<sup>I</sup>M<sup>III</sup>P<sub>2</sub>O<sub>7</sub> (A = alkali metal) families. Although the bulk Li-ion conductivity is low, as determined from alternating-current impedance spectroscopy and variable-temperature static <sup>7</sup>Li NMR spectra, a detailed analysis of the topologies of all seven structure types through bond-valence-sum mapping suggests a potential avenue for enhancing the conductivity. The new polymorph exhibits long (>4 Å) Li-Li distances, no Li vacancies, and an absence of Li pathways in the <i>c</i> direction, features that could contribute to the observed low Li-ion conductivity. In contrast, we found favorable Li-site topologies that could support long-range Li migration for two structure types with modest DFT total energies relative to the new polymorph. These promising structure types could possibly be accessed from innovative doping of the new polymorph.
| Item Type: | Article |
|---|---|
| Divisions: | Faculty of Science and Engineering > School of Physical Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 13 Sep 2021 09:09 |
| Last Modified: | 17 Oct 2023 20:24 |
| DOI: | 10.1021/acs.inorgchem.1c01396 |
| Related URLs: | |
| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3136936 |
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