Published: September 30, 2018
Beekman Mathew, James A. Kaduk, Winnie K. Wong-Ng, George S. Nolas
The low-density clathrate-II modification of silicon, Si136, contains two distinct cage-like voids large enough to accommodate various types of guest atoms which influence both the host structure and its properties. Although the linear coefficient of thermal expansion of Si136 (293 K < T < 423 K) is only about 20% larger than that of the ground state alpha-Si (diamond structure), the coefficient of thermal expansion monotonically increases by more than 150% upon filling the framework cages with Na atoms in NaxSi136 (0 < x < 24), ranging from alpha = 2.6 x 10-6 K- 1 (x = 0) to 6.75 x 10-6 K-1 (x = 24) by only varying the Na content, x. Taken together with the available heat capacity and bulk modulus data, the dramatic increase in thermal expansion can be attributed almost entirely to an increase in the mode-averaged Grüneisen parameter by a factor of more than 2 from x = 0 to x = 24. The results highlight a potential mechanism for tuning thermal expansion, whereby guest atoms are incorporated into the voids of rigid, covalently bonded inorganic frameworks to influence the lattice dynamics.
Citation: Applied Physics Letters
Pub Type: Journals
Type-II clathrate, thermal expansion, Grüneisen parameter, NaxSi136 (x = 1.1, 5.5, 12.6, 17.3, and 21.9)
Created September 30, 2018, Updated March 25, 2019