Structure and phase transition of Sn-substituted Zr_(1−x)Sn_xW₂O₈

Abstract

A conventional solid state reaction between ZrO 2 , SnO 2 and WO 3 was used to prepare the negative thermal expansion material Zr (12x) Sn x W 2 O 8 . The strong negative thermal expansion over a broad temperature range, which is well known for the pure zirconium tungstate compound, is also demonstrated in this substituted material. However, the order-disorder phase transition of the cubic materials was shown to shift towards lower temperatures, dependent on the degree of Sn 41 -substitution, by dilatometry and temperature variable X-ray diffraction. This is attributed to the lower bond strength of the Sn-O bond in comparison to the Zr-O bond. The unit cell parameters of the material are significantly smaller due to the insertion of smaller Sn 41 -cations on the Zr 41 -position in the structure. For one composition (x ~0.3), the structure of Zr (12x) Sn x W 2 O 8 was studied by neutron diffraction at two temperatures, 293 K and 473 K, corresponding to respectively the low temperature a-, and high temperature b-polymorph of Zr (12x) Sn x W 2 O 8 . The refined structures were found to be similar to that of ZrW 2 O 8 at the same temperatures. Variable temperature X-ray diffraction of the same sample was used to establish the phase transition temperature, by refining the fractional occupancy of the possible tungstate orientations with temperature.

Neutron diffraction study of Levantine Middle Bronze Age cast axes

“…These lines are strongest on both edges of the studied axes (close to the edge of the blade, and in the handle). The intensities and positions of the impurity lines are in agreement with the CuCl [7], Cu 2 O [10], SnO 2 [8], and Pb [9] phases for the tin bronze axes. Except for SnO 2 the same impurity lines appear in the diffraction patterns of the arsenical copper axes.…”

“…Data (d-range between 1.25 Å -2.9 Å) were analyzed in detail using the Rietveld refinement method with the GSAS (EXPGUI) code [5,6]. The refined model contained between 16 and 22 variables including phases weight fraction values, cell parameters (with starting values taken from the corresponding literature [7][8][9][10]), background, and scale factors. For peak-shape modeling we used the time-of-flight function #3 available in the GSAS code ( [5], and references therein), usually used for ENGIN-X data analysis, by refining only σ 1 for the main solid solution phases.…”

Effect of Yb substitution on microstructure, physical and mechanical properties of negative thermal expansion Zr1−xYbxWMoO8−x/2 (x=0–0.05) ceramic

“…Significant efforts have been made to shift T c by adjusting compound composition without changing the NTE property. The most extensively studied is Zr 1−x A x W 2 O 8 family of compounds, in which A could be tetravalent or trivalent cations such as Hf 4+ [2,4], Sn 4+ [5], Ti 4+ [6], Sc 3+ , In 3+ , Y 3+ [7], Lu 3+ [8], Eu 3+ , Er 3+ and Yb 3+ [9]. Substitution of W 6+ is also widely studied, where the best known case is ZrMo 2 O 8 .…”

Synthesis, structure and negative thermal expansion of cubic zrw2−xvxo8−x/2 solid solutions

“…To overcome this phase transition and improve thermal stability for potential material applications, cation substituted solid solutions have been researched. It is known that the Zr 4+ can be substituted by such lower valent cations as In 3+ and RE 3+ (RE = Sc, Y, Eu, Er, Yb, Lu) and by equivalent cations Ti 4+ , Sn 4+ and Hf 4+ , though solid solubility of these elements is below 5% except for Sn 4+ which is 20%, and for the same group element Hf 4+ which is 100% [7][8][9][10][11][12][13]. As for W 6+ , successful substitution was previously limited to the same group element Mo 6+ only [14].…”