Large Negative Thermal Expansion and Anomalous Behavior on Compression in Cubic ReO ₃ -Type A ^II B ^IV F ₆ : CaZrF ₆ and CaHfF ₆

Journal Article · Tue Jun 09 00:00:00 EDT 2015 · Chemistry of Materials

DOI:https://doi.org/10.1021/acs.chemmater.5b00662· OSTI ID:1391823

Hancock, Justin C.; Chapman, Karena W.; Halder, Gregory J.; Morelock, Cody R.; Kaplan, Benjamin S.; Gallington, Leighanne C.; Bongiorno, Angelo; Han, Chu; Zhou, Si; Wilkinson, Angus P.

CaZrF6 and CaHfF6 display much stronger negative thermal expansion (NTE) (alpha(L100 K) similar to -18 and -22 ppm K-1, respectively) than ZrW2O8 and other corner-shared framework structures. Their NTE is comparable to that reported for framework solids containing multiatom bridges, such as metal cyanides and metal-organic frameworks. However, they are formable as ceramics, transparent over a wide wavelength range and can be handled in air; these characteristics can be beneficial for applications. The NTE of CaZrF6 is strongly temperature-dependent, and first-principles calculations show that it is largely driven by vibrational modes below similar to 150 cm(-1). CaZrF6 is elastically soft with a bulk modulus (K-300K) of 37 GPa and, upon compression, starts to disorder at similar to 400 MPa. The strong NTE of CaZrF6, which remains cubic to <10 K, contrasts with cubic CoZrF6, which only displays modest NTE above its rhombohedral to cubic phase transition at similar to 270 K. CaZrF6 and CaHfF6 belong to a large and compositionally diverse family of materials, A(II)B(IV)F(6), providing for a detailed exploration of the chemical and structural factors controlling NTE and many opportunities for the design of controlled thermal expansion materials.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science - Office of Basic Energy Sciences - Scientific User Facilities Division; Georgia Institute of Technology
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1391823
• Journal Information: Chemistry of Materials, Vol. 27, Issue 11; ISSN 0897-4756
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English