Controlling superstructural ordering in the clathrate-I Ba8M16P30 (M = Cu, Zn) through the formation of metal–metal bonds
Order–disorder–order phase transitions in the clathrate-I Ba8Cu16P30 were induced and controlled by aliovalent substitutions of Zn into the framework. Unaltered Ba8Cu16P30 crystallizes in an ordered orthorhombic (Pbcn) clathrate-I superstructure that maintains complete segregation of metal and phosphorus atoms over 23 different crystallographic positions in the clathrate framework. The driving force for the formation of this Pbcn superstructure is the avoidance of Cu–Cu bonds. This superstructure is preserved upon aliovalent substitution of Zn for Cu in Ba8Cu16–xZnxP30 with 0 < x < 1.6 (10% Zn/Mtotal), but vanishes at greater substitution concentrations. Higher Zn concentrations (up to 35% Zn/Mtotal) resulted in the additional substitution of Zn for P in Ba8M16+yP30–y (M = Cu, Zn) with 0 ≤ y ≤ 1. This causes the formation of Cu–Zn bonds in the framework, leading to a collapse of the orthorhombic superstructure into the more common cubic subcell of clathrate-I (Pmn). In the resulting cubic phases, each clathrate framework position is jointly occupied by three different elements: Cu, Zn, and P. Detailed structural characterization of the Ba–Cu–Zn–P clathrates-I via single crystal X-ray diffraction, joint synchrotron X-ray and neutron powder diffractions, pair distribution function analysis, electron diffraction and high-resolution electron microscopy, along with elemental analysis, indicates that local ordering is present in the cubic clathrate framework, suggesting the evolution of Cu–Zn bonds. For the compounds with the highest Zn content, a disorder–order transformation is detected due to the formation of another superstructure with trigonal symmetry and Cu–Zn bonds in the clathrate-I framework. It is shown that small changes in the composition, synthesis, and crystal structure have significant impacts on the structural and transport properties of Zn-substituted Ba8Cu16P30.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
- DOE Contract Number:
- SC0008931; AC02-06CH11357; AC05-00OR22725
- OSTI ID:
- 1368265
- Journal Information:
- Chemical Science, Vol. 8, Issue 5; ISSN 2041-6520
- Publisher:
- Royal Society of Chemistry
- Country of Publication:
- United States
- Language:
- ENGLISH
High-efficiency thermoelectric Ba 8 Cu 14 Ge 6 P 26 : bridging the gap between tetrel-based and tetrel-free clathrates
|
journal | January 2017 |
Phonon glass behavior beyond traditional cage structures: synthesis, crystal and electronic structure, and properties of KMg 4 Sb 3
|
journal | January 2018 |
Synthesis, structure, and transport properties of Ba 8 Cu 16 – x Au x P 30 clathrate solid solution
|
journal | February 2020 |
Similar Records
Unconventional Clathrates with Transition Metal–Phosphorus Frameworks
Chemical Bonding and Transport Properties in Clathrates-I with Cu–Zn–P Frameworks