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Synthesis and Characterization of Na4Si2Se6-tP24 and Na4Si2Se6-oP48, Two Polymorphs with Different Anionic Structures
Franziska Kamm1, Florian Pielnhofer1, Marc Schlosser1
1Institut für Anorganische Chemie, Universität Regensburg, 93053 Regensburg, Germany.
Inorganic Chemistry
|June 29, 2023
Summary
Two new polymorphs of sodium selenosilicate (Na4Si2Se6) were synthesized, exhibiting distinct crystal structures and similar energies. The low-temperature phase shows promising ionic conductivity for solid-state applications.
Area of Science:
- Solid-state chemistry and materials science.
- Crystallography and structural characterization.
- Computational materials modeling and ionic conductivity.
Background:
- Exploration of novel inorganic compounds with potential applications in energy storage.
- Understanding structure-property relationships in complex chalcogenides.
Purpose of the Study:
- Synthesize and characterize new polymorphs of sodium selenosilicate (Na4Si2Se6).
- Investigate the structural, energetic, and conductive properties of these new materials.
Main Methods:
- Solid-state synthesis reactions.
- Single-crystal and powder X-ray diffraction for structural determination.
- Density functional theory (DFT) modeling for energetic comparisons.
- Impedance spectroscopy for ionic conductivity measurements.
Main Results:
- Two novel polymorphs, Na4Si2Se6-tP24 (tetragonal) and Na4Si2Se6-oP48 (orthorhombic), were successfully synthesized.
- Both polymorphs represent new structure types, with distinct structural motifs (isolated Si2Se6 units vs. 1D chains).
- DFT calculations indicate the polymorphs are energetically very close (ΔE = 3.4 kJ/mol).
- The Na4Si2Se6-oP48 phase exhibits ionic conductivity (σspec up to 6.8 × 10-6 S/cm at 200°C) with an activation energy of 0.54 eV.
Conclusions:
- The synthesis and characterization of two new Na4Si2Se6 polymorphs expand the known structural diversity of selenosilicates.
- The close energetic proximity suggests potential for interconversion or discovery of other related phases.
- The observed ionic conductivity in the Na4Si2Se6-oP48 polymorph highlights its potential as a solid electrolyte material.
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