biostudies-literatureDolyniuk JBasic Energy Sciences3650-3659https://www.ebi.ac.uk/biostudies/studies/S-EPMC5437377biostudies-literatureUnknown8(5)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 (<i>Pbcn</i>) 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 <i>Pbcn</i> superstructure is the avoidance of Cu-Cu bonds. This superstructure is preserved upon aliovalent substitution of Zn for Cu in Ba₈Cu_16-<i>x</i> Zn _<i>x</i> P₃₀ with 0 < <i>x</i> < 1.6 (10% Zn/M_total), but vanishes at greater substitution concentrations. Higher Zn concentrations (up to 35% Zn/M_total) resulted in the additional substitution of Zn for P in Ba₈M_16+<i>y</i> P_30-<i>y</i> (M = Cu, Zn) with 0 ≤ <i>y</i> ≤ 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 (<i>Pm</i>3<i>n</i>). 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 <i>via</i> 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.Chemical scienceControlling superstructural ordering in the clathrate-I Ba₈M₁₆P₃₀ (M = Cu, Zn) through the formation of metal-metal bonds.PMC5437377DE-AC02-06CH11357DE-SC0008931Dolyniuk JKovnir KLee KWhitfield PSLebedev OIfalseControlling 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 (<i>Pbcn</i>) 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 <i>Pbcn</i> superstructure is the avoidance of Cu-Cu bonds. This superstructure is preserved upon aliovalent substitution of Zn for Cu in Ba₈Cu_16-<i>x</i> Zn _<i>x</i> P₃₀ with 0 < <i>x</i> < 1.6 (10% Zn/M_total), but vanishes at greater substitution concentrations. Higher Zn concentrations (up to 35% Zn/M_total) resulted in the additional substitution of Zn for P in Ba₈M_16+<i>y</i> P_30-<i>y</i> (M = Cu, Zn) with 0 ≤ <i>y</i> ≤ 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 (<i>Pm</i>3<i>n</i>). 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 <i>via</i> 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 Ba₈Cu₁₆P₃₀.2017-01-01T00:00:00Z2017 May2026-05-05T20:28:54.107Z2019-03-27T02:45:25ZS-EPMC54373772858010310.1039/c7sc00354d