A large family of filled skutterudites stabilized by electron count

Abstract

The Zintl concept is important in solid-state chemistry to explain how some compounds that combine electropositive and main group elements can be stable at formulas that at their simplest level do not make any sense. The electronegative elements in such compounds form a polyatomic electron-accepting molecule inside the solid, a 'polyanion', that fills its available energy states with electrons from the electropositive elements to obey fundamental electroncounting rules. Here we use this concept to discover a large family of filled skutterudites based on the group 9 transition metals Co, Rh, and Ir, the alkali, alkaline-earth, and rare-earth elements, and Sb 4 polyanions. Forty-three new filled skutterudites are reported, with 63 compositional variations-results that can be extended to the synthesis of hundreds of additional new compounds. Many interesting electronic and magnetic properties can be expected in future studies of these new compounds.

Effects of partial La filling and Sb vacancy defects on CoSb3 skutterudites

“…Table I summarizes the filling fraction, Sb vacancy, lattice constant, conductivity type, and carrier concentration from a limited number of experimental studies on La-filled CoSb 3 [43,44,45]. For simplicity, a few experimental studies on La-filled CoSb 3 with simultaneous doping at the Co or Sb sites are excluded [24,29,32]. Note that all of the experimental samples have a partial La filling that is lower than the experimental filling fraction limit (FFL) of 23% found by Nolas et al [45].…”

“…While the high mobility is thermoelectrically favorable, the high lattice thermal conductivity is not. To improve the performance of CoSb 3 toward state-of-the-art mid-temperature thermoelectric materials, extensive experimental and theoretical investigations have focused on filling the naturally formed nanosized cages with alkali metals, alkaline earth metals, or rare earth filler atoms [17,18,19,20,21], or doping at the Co and/or Sb sites [22,23], or implementing both measures simultaneously [24,25,26,27,28,29]. In the context of phonon-glass electron-crystal paradigm [3,30], the filler atoms rattle in the cage and strongly scatter the heat-carrying phonons towards a phonon-glass behavior [31], while the dopants optimize the electronic band structure towards an electron-crystal behavior [32].…”

Arsenic chemistry of iron-based superconductors and strategy for novel superconducting materials

“…This can be seen in the BaCu 2 As 2 shown in Figure 1(c), or in the collapsed tetragonal structure of the 122-type iron-based superconductor CaFe 2 As 2 [7][8][9][10][11][12][13][14]. Furthermore, in As 3-(4p 6 ) with an additional electron, the 4p orbital becomes a closed shell, and arsenic does not form a covalent bond. As a result, arsenic becomes the isolated anion As 3-.…”

“…Zigzag chains appear in the 112-type iron-based superconductor Ca 1-x La x FeAs 2 (space group P2 1 , C 2 2 , #4), as shown in Figure 1(b) [1][2][3][4][5]. Tetramers appear in CoAs 3 and other Skutterudites [6]. Since As 2-(4p 5 ) has a single unpaired electron, arsenic makes a single chemical bond.…”

“…That is, arsenic, as seen with As 0 (4p 3 ), As -(4p 4 ), As 2-(4p 5 ), and As 3-(4p 6 ), takes various valence states (electron configurations).…”