Role of Anion Site Disorder in the Near Zero Thermal Expansion of Tantalum Oxyfluoride

详细信息    查看全文

• 作者：Cody R. Morelock ; Benjamin K. Greve ; Mehmet Cetinkol ; Karena W. Chapman ; Peter J. Chupas ; Angus P. Wilkinson
• 刊名：Chemistry of Materials
• 出版年：2013
• 出版时间：May 14, 2013
• 年：2013
• 卷：25
• 期：9
• 页码：1900-1904
• 全文大小：293K
• 年卷期：v.25,no.9(May 14, 2013)
• ISSN：1520-5002

文摘

Materials with the cubic ReO₃-type structure are, in principle, excellent candidates for negative thermal expansion (NTE). However, many such materials, including TaO₂F, do not display NTE. It is proposed that local distortions away from the ideal structure, associated with the need to accommodate the different bonding requirements of the disordered O/F, contribute to the occurrence of near zero thermal expansion rather than NTE. The local structure of TaO₂F is poorly described by an ideal cubic ReO₃-type model with O and F randomly distributed over the available anion sites. A supercell model featuring 鈭扵a鈥揙鈥揟a鈥揙鈥揟a鈥揊鈥?chains along 1 0 0, with different Ta鈥揙 and Ta鈥揊 distances and O/F off-axis displacements, gives much better agreement with pair distribution functions (PDFs) derived from total X-ray scattering data for small separations (<8 脜). Analyses of PDFs derived from variable temperature measurements (80 to 487 K), over different length scales, indicate an average linear expansion coefficient of close to zero with similar contributions from the geometrically distinct Ta鈥揙鈥擳a and Ta鈥揊鈥擳a links in TaO₂F.

Keywords:

anion site disorder; tantalum oxyfluoride; near zero thermal expansion; pair distribution functions