A novel clathrate phase, Ba8Au16P30, was synthesized from its elements. High-resolution powder X-ray diffraction and transmission electron microscopy were used to establish the crystal structure of the new compound. Ba8Au16P30 crystallizes in an orthorhombic superstructure of clathrate-I featuring a complete separation of gold and phosphorus atoms over different crystallographic positions, similar to the Cu-containing analogue, Ba8Cu16P30. Barium cations are trapped inside the large polyhedral cages of the gold–phosphorus tetrahedral framework. X-ray diffraction indicated that one out of 15 crystallographically independent phosphorus atoms appears to be three-coordinate. Probing the local structure and chemical bonding of phosphorus atoms with 31P solid-state NMR spectroscopy confirmed the three-coordinate nature of one of the phosphorus atomic positions. High-resolution high-angle annular dark-field scanning transmission electron microscopy indicated that the clathrate Ba8Au16P30 is well-ordered on the a...

Clathrate Ba8Au16P30: the "gold standard" for lattice thermal conductivity.

Several efficient thermoelectric materials have been found among the ternary Zintl antimonides. If the band structure is highly asymmetric around the band gap, the efficiency as either n- or p-type may differ significantly. The Zintl antimonides have generally been found to be p-type. Surprisingly, this also holds true for the narrow band gap binary ZnSb and Zn4Sb3. Using ab initio calculations, we investigate intrinsic point defects in ZnSb as a possible origin of the p-type conductivity. Only Zn vacancies are found to be present in significant amounts at room temperature. The low formation energy of negatively charged Zn defects pins the electronic chemical potential to the lower part of the band gap leading to intrinsic ZnSb being p-type. We discuss this finding as a general explanation of p-type conductivity in Zintl antimonides, and how to overcome the doping limits in these materials.

Ab initio Calculations of Intrinsic Point Defects in ZnSb

Zintl phases with group 15 elements and the transition metals: A brief overview of pnictides with diverse and complex structures

The first arsenide clathrates A_8Zn_(18)As_(28) (A = K, Rb, Cs) and Cs_8Cd_(18)As_(28) have been synthesized in high yields via a two-step route. These compounds adopt the type-I structure and exhibit structural characteristics different from the recently reported antimonide clathrates Cs_8Zn_(18)Sb_(28) and Cs_8Cd_(18)Sb_(28). In arsenide clathrates, Zn (or Cd) and As atoms are statistically mixed at the three framework sites: 6c, 16i, and 24k; the alkali metals reside inside the cages at the 2a and 6d sites, with the 2a site being only partially filled. Single-crystal X-ray diffraction studies confirm that the Cd atoms preferably occupy the 6c and 24k sites over the 16i site, with more than 80% of Cd found at the former two positions. A unique structural feature is a framework disorder coupled with the partial occupancy of the cage’s 2a site. Optical absorption measurements and electronic property measurements reveal a semimetallic-like behavior for Cs_8Cd_(18)As_(28) and semiconductor-like behavior for A_8Zn_(18)As_(28) (A = Rb, Cs).

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Synthesis, Structural Characterization, and Physical Properties of the Type‑I Clathrates A_8Zn_(18)As_(28) (A = K, Rb, Cs) and Cs_8Cd_(18)As_(28)

ConspectusIn this Account, we focused on a unique class of inclusion compounds, intermetallic clathrates, which exist in a variety of structures and exhibit diverse physical properties. These compounds combine covalent tetrahedral frameworks with rattling guest atoms situated inside their framework cages. Tetrels, the group 14 elements, are the basis for conventional clathrates because they fulfill the bonding requirement of four electrons per framework atom. In analogy to the replacement of Ge with GaAs in semiconductors, we focused on unconventional tetrel-free clathrates with frameworks composed of phosphorus and late transition metals. Compared to tetrels, these elements exhibit greater flexibility in their local coordinations and bonding. Tetrel elements cannot tolerate high deviations from regular tetrahedral coordinations. Thus, they exile a number of theoretically predicted framework topologies that are composed of a single type of polyhedral cage with square faces, such as the truncated octahedro...

https://pubs.acs.org/doi/pdf/10.1021/acs.accounts.7b00469

Unconventional Clathrates with Transition Metal-Phosphorus Frameworks.

A novel ternary antimonide Rb16Cd25.39(3)Sb36 has been synthesized by a solid-state reaction of the appropriate amount of elements in a welded niobium tube at 530 °C. The compound crystallizes in orthorhombic space group Cmcm (No. 63) with a = 16.499(5) A, b = 12.391(4) A, c = 12.400(4) A, and Z = 1. The structure features a new 3D network constructed of chains of Rb+-centered dodecahedra running along [001]. The atomic distribution of the Cd8Sb12 dodecahedron presents an energetically favored pattern without any Cd−Cd bonding. The formation of the phase and the occurrence of a very narrow phase width of Rb16Cd24+xSb36 [0.94(2) ≤ x ≤ 1.47(3)] have been studied in detail. The Fermi level of the title compound is expected to be located between those of the hypothetical models of “[Rb16Cd24Sb36]0” (I, poor metallic) and “[Rb16Cd24Sb36] + 4e” (II, narrow-band-gap semiconductor), which agrees well with the experimental measurements. In the temperature range of 300−473 K, the as-synthesized Rb16Cd25.39(3)Sb36 e...

Rb16Cd25.39(3)Sb36: An Electron-Deficient Zintl Phase Containing Infinite Dodecahedron Chains

A new caged Cu-rich antimonide, BaCu7.31(3)Sb5, was obtained from a direct combination of the elements in a graphite crucible under a high vacuum by a solid state reaction, and the structure was determined by the single-crystal X-ray diffraction method to be hexagonal P63/mmc (No.194), with a = 7.0154(4) A, c = 12.5423(14) A, V = 534.58(7) A3, and Z = 2. BaCu7.31(3)Sb5 is the first antimonide member of the BaNi9P5-type barium copper pnictides with a Cu2 site occupancy of 43.7(9)%, and the structure building unit is a 30-vertex Cu18Sb12 cage centered by a Ba atom. The Cu18Sb12 cages form chains along the c axis by sharing the opposite hexagonal (Cu2)3(Sb2)3 faces. Such a cage chain shares (Cu1)2(Sb1)2 rhomboidal faces with six neighboring chains along the [100], [010], and [110] directions to generate a 3D condensed metallic network. The electronic structure calculations by CASTEP indicate the metallic nature, which matches well with the metallic electrical conductivity, small Seebeck coefficient, and Paul...

Synthesis, Crystal and Electronic Structures, and Physical Properties of Caged Ternary Cu-Rich Antimonide: BaCu7.31(3)Sb5

The invention discloses a novel Zintl-phase thermoelectric compound and a preparation method thereof, and belongs to the field of inorganic materials. The compound is synthesized by a one-step synthesis method. The synthetic condition is that the reaction is performed for 6 days at the temperature of 530 DEG C. In the invention, the compound Rb16Cd25.39(3)Sb36 is structurally characterized by containing infinite dodecahedron cage chains along the c-axis direction, one 10-ring channel is enclosed by every four adjacent cage chains, and alkali metal Rb is filled into the centers and channels of dodecahedrons. The electron-deficient Zintl-phase material has the advantages that: the chemical purity is high, the uniformity is high, and components are controllable. The electron-deficient Zintl-phase Rb16Cd25.39(3)Sb36 containing the infinite cage chains successfully expands the range of experimental and theoretical research of Sb-containing cage compounds. In the invention, the thermoelectric figure of merit (ZT) value of the undoped compound Rb16Cd25.39(3)Sb36 reaches 0.04 at the temperature of 466K, and is equivalent to that of a skutterudite compound, which indicates that the compound highly possibly realizes a higher ZT value through structural modification and doping and has potential application value.

Novel Zintl-phase thermoelectric compound and preparation method thereof

The new title compound is synthesized by solid state reaction of the elements (Nb tube, 530 °C, 160 h) and characterized by single crystal XRD, electrical and thermal transport measurements, and LAPW electronic structure calculations.

Rb16Cd25.39(3)Sb36: An Electron-Deficient Zintl Phase Containing Infinite Dodecahedron Chains.

The title compound is prepared by solid state reaction of the elements (graphite crucible, 950 °C, 80 h) and characterized by single crystal XRD, electrical conductivity and magnetic susceptibility measurements, and CASTEP electronic band structure calculations.

Wu-Zui Zheng

Papers

Rb16Cd25.39(3)Sb36: An Electron-Deficient Zintl Phase Containing Infinite Dodecahedron Chains

Synthesis, Crystal and Electronic Structures, and Physical Properties of Caged Ternary Cu-Rich Antimonide: BaCu7.31(3)Sb5

Novel Zintl-phase thermoelectric compound and preparation method thereof

Rb16Cd25.39(3)Sb36: An Electron-Deficient Zintl Phase Containing Infinite Dodecahedron Chains.

Synthesis, Crystal and Electronic Structures, and Physical Properties of Caged Ternary Cu-Rich Antimonide: BaCu7.31(3)Sb5.