Large Positive Thermal Expansion and Small Band Gap in Double-ReO3-Type Compound NaSbF6

C Yang; B Y Qu; S S Pan; L Zhang; R R Zhang; P Tong; R C Xiao; J C Lin; X G Guo; K Zhang; H Y Tong; W J Lu; Y Wu; S Lin; W H Song; Y P Sun

doi:10.1021/acs.inorgchem.7b00002

Large Positive Thermal Expansion and Small Band Gap in Double-ReO₃-Type Compound NaSbF₆

Inorg Chem. 2017 May 1;56(9):4990-4995. doi: 10.1021/acs.inorgchem.7b00002. Epub 2017 Apr 13.

Authors

C Yang^{1

2}, B Y Qu³, S S Pan¹, L Zhang⁴, R R Zhang⁴, P Tong¹, R C Xiao^{1

2}, J C Lin¹, X G Guo^{1

2}, K Zhang^{1

2}, H Y Tong^{1

2}, W J Lu¹, Y Wu¹, S Lin¹, W H Song¹, Y P Sun^{1

4

5}

Affiliations

¹ Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences , Hefei 230031, People's Republic of China.
² University of Science and Technology of China , Hefei 230026, People's Republic of China.
³ Laboratory of Amorphous Materials, School of Materials Science and Engineering, Hefei University of Technology , Hefei 230009, People's Republic of China.
⁴ High Magnetic Field Laboratory, Chinese Academy of Sciences , Hefei 230031, People's Republic of China.
⁵ Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, People's Republic of China.

PMID: 28406625
DOI: 10.1021/acs.inorgchem.7b00002

Abstract

Double-ReO₃-type structure compound NaSbF₆ undergoes a low-temperature rhombohedral to high-temperature cubic phase between 303 and 323 K, as revealed by temperature-dependent X-ray diffractions. Although many double-ReO₃-type fluorides exhibit either low thermal expansion or negative thermal expansion (NTE), NaSbF₆ exhibits positive thermal expansion (PTE) with a large volumetric coefficient of thermal expansion, α_v = 62 ppm/K, in its cubic phase. Raman spectroscopy reveals that the low-frequency transverse vibration of fluorine atoms is stiffened in NaSbF₆, compared with the typical NTE compound CaZrF₆ with the same structure. The related weak contraction associated with the polyhedral rocking would be overcome by the notable elongation of the Na-F bond length on heating, thus leading to the large volumetric PTE. Unlike ScF₃ and CaZrF₆ which are insulators with a wide band gap, a relative small band gap of 3.76 eV was observed in NaSbF₆. The small band gap can be attributed to the hybridization between the Sb 5s and F 2p orbitals.