Sumithra, S and Umarji, AM (2004) Role of crystal structure on the thermal expansion of $Ln_2W_3O_1_2$ (Ln =La, Nd, Dy, Y, Er and Yb). In: Solid State Sciences., 6 (12). pp. 1313-1319.
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The negative thermal expansion material $Y_2W_3O_1_2$ belongs to $Ln_2W_3O_1_2$ family of compositions. The thermal expansion behavior of $Ln_2W_3O_1_2$ (Ln = La, Nd, Dy, Y, Er and Yb) members synthesized by the solid-state reaction have been studied and correlated to their crystal structure. The lighter rare earth tungstates (Ln = La, Nd and Dy) crystallize in monoclinic structure (C2/c) whereas the heavy rare earth tungstates (Ln = Y, Er and Yb) form the trihydrate orthorhombic $Ln_2W_3O_1_2·3H_2O$ at room temperature and above 400 K transforms to unhydrated orthorhombic structure (Pnca). The hot pressed (1273 K and 25 MPa) ceramic pellets have been studied for thermal expansion property by dilatometry and high temperature X-ray diffraction. The heavy rare earth tungstates show a large initial expansion up to 400 K, followed by a thermal contraction. The light rare earth tungstates, on the other hand, show thermal expansion. The difference in the thermal expansion behavior in $Ln_2W_3O_1_2$ series is attributed to the difference in the structural features. The heavy rare earth tungstates have corner sharing of $LnO_6$ octahedra with $WO_4$ tetrahedra, where the now well established mechanism of transverse vibrations operate. The light rare earth tungstates have edge sharing of $LnO_8$ polyhedra where in such a mechanism is absent.
|Item Type:||Journal Article|
|Additional Information:||The copyright of this article belongs to Elsevier.|
|Keywords:||Rare earth tungstates;Thermal expansion;Crystal structure|
|Department/Centre:||Division of Chemical Sciences > Materials Research Centre|
|Date Deposited:||03 Apr 2006|
|Last Modified:||19 Sep 2010 04:25|
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