Synthesis, reversibility and mechanism of the dehydration of monoclinic CaZn{sub 2}(PO{sub 4}){sub 2}·2H{sub 2}O

Journal Article · Sat Sep 15 04:00:00 EDT 2018 · Journal of Solid State Chemistry (Print)

DOI:https://doi.org/10.1016/J.JSSC.2018.06.022· OSTI ID:22890217

Sharma, S.; Trettin, R. ^[1]

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1. University of Siegen, Paul-Bonatz-Str. 9-11, Siegen, 57076 (Germany)

Highlights: • Reversibility of dehydration of synthetic monoclinic CaZn{sub 2}(PO{sub 4}){sub 2}·2H{sub 2}O to CaZn{sub 2}(PO{sub 4}){sub 2}·H{sub 2}O is proven. • Morphological changes upon dehydration to mono- and anhydrate are investigated. • The diffraction pattern of the monohydrate is presented and indexed. • Lattice constants up to the monohydrate are derived from in-situ XRD measurements. • A topotactic dehydration mechanism is deduced. - Abstract: The reversibility of the dehydration of monoclinic CaZn{sub 2}(PO{sub 4}){sub 2}·2H{sub 2}O to the corresponding monohydrate is proven and the dehydration enthalpy determined by combination of thermal analysis and X-ray diffraction. The mechanism of the monohydrate formation is investigated by scanning electron microscopy (SEM) and temperature dependent in situ X-ray powder diffraction. Mechanistic impact on the powder bulk properties are deduced. As for the orthorhombic dimorph, a crystalline monohydrate species is identified and firstly indexed. Thermal induced changes of the lattice parameters up to the formation of the monohydrate are analyzed. A linear elongation of the lattice parallel to the directions [100] and [001] is found. The corresponding elongation coefficients and the volumetric expansion of the unit cell are determined. With regard to the option of synthetic production of the compound, a possible application of the material for thermochemical energy storage and conversion is conceivable. The relevance of fundamental mechanistic features on the bulk behaviour upon cyclic de- and rehydration is discussed.

• OSTI ID: 22890217
• Journal Information: Journal of Solid State Chemistry (Print), Journal Name: Journal of Solid State Chemistry (Print) Vol. 265; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: Netherlands
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CALCIUM PHOSPHATES
DEHYDRATION
HYDRATES
LATTICE PARAMETERS
MONOCLINIC LATTICES
ORTHORHOMBIC LATTICES
SCANNING ELECTRON MICROSCOPY
TEMPERATURE DEPENDENCE
THERMAL ANALYSIS
WATER
X-RAY DIFFRACTION
ZINC PHOSPHATES