The remarkable crystal chemistry of the Ca14AlSb11 structure type, magnetic and thermoelectric properties

Yufei Hu,Giacomo Cerretti,Elizabeth L Kunz Wille,Sabah K Bux,Susan M Kauzlarich

doi:10.1016/j.jssc.2018.12.037

Abstract

Yb14MnSb11 is a member of a remarkable structural family of compounds that are classified according to the concept of Zintl. This structure type, of which the prototype is Ca14AlSb11, provides a flexible framework for tuning structure-property relationships and hence the physical and chemical properties of compounds. Compounds within this family show exceptional high temperature thermoelectric performance at temperatures above 300 K and unique magnetic and transport behavior at temperatures below 300 K. This review provides an overview of the structure variants, the magnetic properties, and the thermoelectric properties. Suggestions for directions of future research are provided.

Highlights

Introduction to Zintl Phase CompoundsNamed after Eduard Zintl, Zintl phases are salt-like intermetallic compounds in which electrons can be considered as completely transferred from cations to anions.[1, 2] In Zintl phases, electronic configurations of both cations and anions usually follow valence rules to have stable electronic configurations
Two recent examples of Mg containing compounds are Sr14MgSb11 and Eu14MgSb11.47 Sr and Eu are similar in charge and size, the two compounds present some crystallographic differences. They both crystalize in the tetragonal crystal group I41/acd, but the Sr analog shows disorder of the Sb3 atom, which results in a long Sb-Sb interaction, similar what has been described for Sr14ZnSb11.35 From the Zintl perspective, the Sr14MSb11 M = Mg, Zn is one electron deficient compared to Ca14AlSb11, due to the difference between the oxidation states of Mg2+, Zn2+ and Al3+
Zintl phases with the Ca14AlSb11 structure type, providing a foundation for future directions

Summary

Introduction to Zintl Phase Compounds

Named after Eduard Zintl, Zintl phases are salt-like intermetallic compounds in which electrons can be considered as completely transferred from cations to anions.[1, 2] In Zintl phases, electronic configurations of both cations and anions usually follow valence rules to have stable electronic configurations. One active research area is to systematically explore more complex compositions such as Ca11Sb10, K4Pb9, Na8Si46, Ca14AlSb11 and KBa2InAs3.3-7 The other direction is to replace the alkaline earth metals with divalent rare earth elements (Sm, Eu and Yb) along with the introduction of transition metals into structures, typically replacing the less electronegative metalloid in the anionic framework.[8,9,10] Combinations of these two directions led to compounds such as Yb14MnSb11, Pr4MnSb9, Eu10Mn6Sb13, Yb9Zn4+xBi9 and Cs13Nb2In6As10.11-16 The complexity of compositions can be combined with a small flexibility in electron counting. With the introduction of transition elements, new electronic properties are possible, but complete transfer of electrons and clear counting of valence electrons remains a criterion for describing transition and rare earth metal containing Zintl phase compounds. Their presence may be important to the electronic bands near Fermi-level as Zintl phase compounds containing these high degeneracy orbitals have dramatically different properties from the analogs without d- and f-orbitals in the structures

A14MPn11 Structure Type

Properties of A14MPn11 Compounds

Findings

Thermoelectric Properties