| Zirconium Tungstate |
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CUBIC PHASE Cubic Zirconium Tungstate (alpha-ZrW2O8), one of the several known Phase s of Zirconium Tungstate (ZrW2O8) is perhaps one of the most studied materials to exhibit Negative Thermal Expansion . It has been shown to contract continuously over a previously unprecedented Temperature range of 2-1050 K. This phase is Thermodynamically Unstable at Room Temperature with respect to the binary Oxides ZrO2 and WO3 , but may be Sythesised by heating these oxides together and then quenching the material by rapidly cooling it from approximately 900 C to room temperature. The structure of Cubic Zirconium Tungstate consists of corner-sharing ZrO6 Octahedral and WO4 Tetrahedral structural units. Its unusual expansion properties are due to vibrational modes known as 'Rigid Unit Modes' (RUMs), which involve the coupled rotation of the polyhedral units that make up the structure, and lead to contraction. HIGH PRESSURE FORMS At High Pressure , zirconium tungsate undergoes a series of Phase Transitions , first to an Amorphous phase, and then to a U3O8-type phase, in which the zirconium and tungsten atoms are disordered. EXTERNAL LINKS |
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