Hygroscopicity and bulk thermal expansion Y2W3O12

Negative thermal expansion material, Y2W3O12 has been synthesized by the solid-state method and bulk thermal expansion of the material has been investigated from 300 to 1100 K. The material reversibly forms a trihydrate composition whose X-ray diffraction pattern can be indexed to an orthorhombic unit cell with a = 10.098(1) Angstrom, b = 13.315(3) Angstrom, c = 9.691(4) Angstrom. The cell volume of the hydrated pattern is 7% smaller than the unhydrated cell volume. According to the dilatometric studies, the material shows a 3-6% increase in the linear strain at about 400 K, which can be attributed to the removal of water. Sintering the material at 1473 K leads to large grain size of > 100 mum, which results in a large hysteresis in the bulk thermal expansion behavior. Hot pressing at 1273 K under a uniaxial pressure of 25 MPa results in a fine-grained (2-5 mum) ceramic. Glazing the ceramic prevents moisture pick up and a linear thermal expansion over the entire temperature range 1100-300 K and an average linear thermal expansion co-efficient of -9.65 x 10(-6)/K is observed. The effect of water on the thermal expansion behavior of this system is discussed. (C) 2004 Elsevier Ltd. All rights reserved.