Hydrated calcium oxalates: Crystal structures, thermal stability and phase evolution

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19 Scopus citations


Thermal stability, structural evolution pathways, and phase transition mechanisms of the calcium oxalates whewellite (CaC 2O 4·H 2O), weddellite (CaC 2O 4·(2+x)H 2O), and caoxite (CaC 2O 4·3H 2O) have been analyzed using single crystal and powder X-ray diffraction (XRD). During single crystal XRD heating experiments, α-CaC 2O 4 and the novel calcium oxalate monohydrate have been obtained and structurally characterized for the first time. The highest thermal expansion of these compounds is observed along the direction of the hydrogen bonds, whereas the lowest expansion and even contraction of the structures occur due to the displacement of neighbor layered complexes toward each other and to an orthogonalization of the monoclinic angles. Within the calcium oxalate family, whewellite should be regarded as the most stable crystalline phase at ambient conditions. Weddellite and caoxite transform to whewellite during dehydration-driven phase transition promoted by time and/or heating.

Original languageEnglish
Pages (from-to)5465–5478
Number of pages14
JournalCrystal Growth and Design
Issue number9
StatePublished - 5 Sep 2018

Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics


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