Zirconium Tingstate – A New Approach to NTE Synthesis

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zirconium tungstate is a material that behaves counterintuitively – it shrinks on heating, unlike the majority of materials that expand. This negative thermal expansion (NTE) property is maintained over a temperature range of 0.31050 K and is isotropic.

NTE materials have numerous applications in precision engineering, optics and structural materials, but they can be difficult to work with, particularly at low temperatures. This article introduces a new approach to synthesis of nanosized zirconium tungstate that overcomes this challenge. Using a combination of electrospinning and pyrolysis, it is possible to produce a highly disperse, amorphous, nano-sized zirconium tungstate with NTE properties. The material is also soluble in a number of organic solvents, which opens the door to the preparation of NTE composites with other materials such as carbon fiber.

The NTE behavior of zirconium tungstate can be explained by the atomic structure and vibrational modes of the material. The cubic zirconium tungsstate structure is comprised of corner-sharing ZrO6 octahedral and WO4 tetrahedral structural units. The structure has P213 space group symmetry at low temperatures. At higher temperatures, a centre of inversion is introduced by the disordering of the orientation of tungstate groups. This leads to the contraction of the unit cell.

The hydration of zirconium tungstate is characterized by a linear decrease in the lattice constant from 9.14 A in the non-hydrated state to 8.84 A in the fully hydrated state. This change is attributed to rotations of the tetrahedral tungsten coordination sites. The resulting structural changes can be described by a vibrational model that includes Rigid Unit Modes.