Synthesis, Structure, and Electrical Properties of the Single Crystal Ba₈Cu₁₆As₃₀

Abstract

Single crystals of clathrate-I BaCuAs have been synthesized and their structure and electronic properties determined using synchrotron-based X-ray diffraction and first-principles calculations. The structure is confirmed to be Pm3̅ n (No. 223), with lattice parameter a = 10.4563(3) Å, and defined by a tetrahedrally bonded network of As and Cu that forms two distinct coordination polyhedra, with Ba residing inside these polyhedra. All crystallographic positions are fully occupied with no vacancies or superstructure with the Cu atoms, while occupying all framework sites in the network, exhibiting a preference for the 6c site. Agreement between the experimental and theoretically predicted structures was achieved after accounting for spin-orbit coupling. Our calculated Fermi surface, electron localization, and charge transfer, as well as a comparison with the results for elemental As, provide insight into the fundamental properties of this clathrate-I material.

III–V Clathrate Semiconductors with Outstanding Hole Mobility: Cs8In27Sb19 and A8Ga27Sb19 (A = Cs, Rb)

“…Conventional clathrates, with frameworks composed of tetrel elements of group 14 (Si, Ge, or Sn), can be partially replaced with group 13 triel elements (Al, Ga, or In) to realize the electron-balanced composition, i.e., four electrons per framework atom in the clathrate to achieve tetrahedral 41 We hypothesized that clathrate frameworks could be composed solely from triels and pnictogens, similar to replacing Ge with GaAs in simple semiconductors. To create a Si-or Ge-free clathrate, two criteria must be met: (i) an electron balance for the composition and (ii) a cation/ framework size match.…”

“…For example, the excess of electrons from K, Cs, or Ba guest cations is compensated with the replacement of tetrel with triel atoms, such as Ba 8 Ga 16 Sn 30 , Cs 8 Ga 8 Si 38 , K 8 In 8 Sn 38 , and Ba 8 Al 16‑x Si 30+ x . Clathrate frameworks can be made tetrel-free, using transition metals and phosphorus frameworks {Ni,Cu,Zn,Au}–P with Ba, Sr, and La as guest cations, e.g., Ba 8 Cu 16 P 30 , Ba 8 Au 16 P 30 , BaNi 2 P 4 , or SrNi 2 P 4 . − To date, few examples of As- or Sb-containing tetrel-free clathrates have been reported: Cs 8 Zn 18 Sb 28 , Rb 8 Zn 18 As 28 , and Ba 8 Cu 16 As 30 . We hypothesized that clathrate frameworks could be composed solely from triels and pnictogens, similar to replacing Ge with GaAs in simple semiconductors.…”

Clathrate XI K58Zn122Sb207: A New Branch on the Clathrate Family Tree

“…[19] There is as mall group of inorganic clathrates whose framework does not contain aGroup 14 element but is based on ametal and pnictogen (P,As, Sb). [20][21][22][23][24][25][26][27][28] Among these tetrelfree clathrates,those containing Pexhibit structural diversity adopting at least three structure types, [13,[20][21][24][25][26] however they are metals,thus not suitable as thermoelectric materials.…”

Clathrate XI K58Zn122Sb207: A New Branch on the Clathrate Family Tree

“…On the contrary,a ll seven clathrates based on heavier pnictogens (As or Sb) belong to the clathrate type Ia nd are narrow-gap semiconductors with fascinating transport properties. [22,23,27,28] Discovery of clathrates of anew type,aswell as anon-tetrel clathrate is exceedingly rare.…”