Dehydration, polymorphism and ionic conductivity of sodium hypodiphosphates

A series of 12 compounds: Na(H<sub>3</sub>P<sub>2</sub>O<sub>6</sub>) (1 and 2), Na(H<sub>3</sub>P<sub>2</sub>O<sub>6</sub>)·H<sub>2</sub>O (3), Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>) (4 and 5), Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>)·2H<sub>2</sub>O (6), Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>)·6H<sub>2</sub>O (7 and 8), Na<sub>5</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>)(HP<sub>2</sub>O<sub>6</sub>)·21H<sub>2</sub>O (9), Na<sub>3</sub>(HP<sub>2</sub>O<sub>6</sub>) (10 and 11) and Na<sub>3</sub>(HP<sub>2</sub>O<sub>6</sub>)·9H<sub>2</sub>O (12) has been characterized by variable-temperature optical microscopy, thermogravimetry, single-crystal and powder X-ray diffraction. Crystalline salts 1-4, 6-10 and 12 have been obtained in typical solution crystallization processes. Dehydrations of Na(H<sub>3</sub>P<sub>2</sub>O<sub>6</sub>)·H<sub>2</sub>O (3), Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>)·6H<sub>2</sub>O (both 7 and 8) and Na<sub>3</sub>(HP<sub>2</sub>O<sub>6</sub>)·9H<sub>2</sub>O (12) were monitored by TGA, variable-temperature microscopy and powder or microsample powder X-ray diffraction, and turned out to be one-step, destructive transformations, resulting in almost pure triclinic form of Na(H<sub>3</sub>P<sub>2</sub>O<sub>6</sub>) (1), α-Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>) (4) and α-Na<sub>3</sub>(HP<sub>2</sub>O<sub>6</sub>) (10), respectively. Sodium ionic conductivity was calculated using the bond valence sum method for all obtained anhydrous substances and measured for the best candidate, compound 4 in the temperature range 300-420 K, reaching 10<sup>-4</sup> S m<sup>-1</sup>.

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Publication Details

Journal
Acta Crystallographica Section B Structural Science Crystal Engineering and Materials
Published
2026-03-24
DOI
https://doi.org/10.1107/s2052520626001514
Primary Topic
Advanced Battery Materials and Technologies
Type
article
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article

Dehydration, polymorphism and ionic conductivity of sodium hypodiphosphates

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials
Advanced Battery Materials and Technologies
article

Dehydration, polymorphism and ionic conductivity of sodium hypodiphosphates

article en

Abstract

A series of 12 compounds: Na(H<sub>3</sub>P<sub>2</sub>O<sub>6</sub>) (1 and 2), Na(H<sub>3</sub>P<sub>2</sub>O<sub>6</sub>)·H<sub>2</sub>O (3), Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>) (4 and 5), Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>)·2H<sub>2</sub>O (6), Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>)·6H<sub>2</sub>O (7 and 8), Na<sub>5</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>)(HP<sub>2</sub>O<sub>6</sub>)·21H<sub>2</sub>O (9), Na<sub>3</sub>(HP<sub>2</sub>O<sub>6</sub>) (10 and 11) and Na<sub>3</sub>(HP<sub>2</sub>O<sub>6</sub>)·9H<sub>2</sub>O (12) has been characterized by variable-temperature optical microscopy, thermogravimetry, single-crystal and powder X-ray diffraction. Crystalline salts 1-4, 6-10 and 12 have been obtained in typical solution crystallization processes. Dehydrations of Na(H<sub>3</sub>P<sub>2</sub>O<sub>6</sub>)·H<sub>2</sub>O (3), Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>)·6H<sub>2</sub>O (both 7 and 8) and Na<sub>3</sub>(HP<sub>2</sub>O<sub>6</sub>)·9H<sub>2</sub>O (12) were monitored by TGA, variable-temperature microscopy and powder or microsample powder X-ray diffraction, and turned out to be one-step, destructive transformations, resulting in almost pure triclinic form of Na(H<sub>3</sub>P<sub>2</sub>O<sub>6</sub>) (1), α-Na<sub>2</sub>(H<sub>2</sub>P<sub>2</sub>O<sub>6</sub>) (4) and α-Na<sub>3</sub>(HP<sub>2</sub>O<sub>6</sub>) (10), respectively. Sodium ionic conductivity was calculated using the bond valence sum method for all obtained anhydrous substances and measured for the best candidate, compound 4 in the temperature range 300-420 K, reaching 10<sup>-4</sup> S m<sup>-1</sup>.

Acta Crystallographica Section B Structural Science Crystal Engineering and MaterialsVol. 82(2)
University of Wrocław (PL), Polish Academy of Sciences (PL)
Openalex Percentile: Top 9%
Advanced Battery Materials and Technologies
DOISourceOpenAlex
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