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zirconium tungstate is an interesting material that exhibits negative thermal expansion (NTE) due to correlated motion of its polyhedral structure units, also called rigid unit modes. This property, coupled with the cubic crystal structure, makes it isotropic and highly stable over its entire stability range.
Cubic ZrW2O8
A cubic form of zirconium tungstate, known as alpha-ZrW2O8, has been shown to exhibit continuous negative thermal expansion over an exceptionally broad temperature range, spanning from 0.3 to 1050 degC. The NTE is based on correlated motions of the corner-sharing ZrO6 octahedral and WO4 tetrahedral structural units that make up this phase.
Synthesis of this phase was a complex process. The basic reaction involved heating stoichiometric quantities of a zinc-free binary oxide, ZrO2, to about 1200 degC. A subsequent step of rapid cooling of the solid to about 900 degC resulted in a crystalline ZrW2O8 phase.
This phase was characterized by X-ray diffraction, CuKa X-ray spectroscopy and Raman scattering analysis. Its crystal structure is P213 space group symmetry with a centre of inversion introduced by disordered tungstate groups.
Obtained through a one-pot reaction of Cr III and ZrIII, these heteropoly-16-tungstates are Cr III-containing tungstates that consist of a tungstic acid unit
The soluble salts of zirconium and its oxidatively converted tungstates are inert to the human body, and the dietary intake of these products is less than 50 microg per day. Soluble forms of zirconium and its salts have a mild systemic toxicity, although the absorbed concentration may be lower in land plants than in water-loving aquatic organisms.