Synthesis and characterization of new ternary transition metal Zintl compounds

A series of new ternary manganese Zintl compounds A{dollar}sb{lcub}14{rcub}{dollar}MnX{dollar}sb{lcub}11{rcub}{dollar} (A = Ca, Sr, Ba; X = As, Sb, Bi) have been synthesized by high temperature routes. These compounds are isostructural to the main group Zintl compounds Ca{dollar}sb{lcub}14{rcub}{dollar}AlSb{dollar}sb{lcub}11{rcub}{dollar} and (Ca,Sr){dollar}sb{lcub}14{rcub}{dollar}GaAs{dollar}sb{lcub}11{rcub}{dollar}, as determined by single crystal and powder X-ray diffraction. The structures are described using the Zintl concept as containing MnX{dollar}sb4sp{lcub}9-{rcub}{dollar} tetrahedra, X{dollar}sb3sp{lcub}7-{rcub}{dollar} linear chains, isolated X{dollar}sp{lcub}3-{rcub}{dollar} anions and isolated A{dollar}sp{lcub}2+{rcub}{dollar} cations.; Temperature dependent magnetic susceptibility measurements indicate that (Ca,Sr){dollar}sb{lcub}14{rcub}{dollar}MnBi{dollar}sb{lcub}11{rcub}{dollar}, (Ca,Sr,Ba){dollar}sb{lcub}14{rcub}{dollar}MnSb{dollar}sb{lcub}11{rcub}{dollar} and Ca{dollar}sb{lcub}14{rcub}{dollar}MnAs{dollar}sb{lcub}11{rcub}{dollar} are ferromagnets at low temperatures. Ba{dollar}sb{lcub}14{rcub}{dollar}MnBi{dollar}sb{lcub}11{rcub}{dollar} is an antiferromagnet and (Sr,Ba){dollar}sb{lcub}14{rcub}{dollar}MnAs{dollar}sb{lcub}11{rcub}{dollar} are paramagnets. All the compounds obey the Curie-Weiss law at high temperatures. The paramagnetic moments for each compound indicate that each Mn has 4 unpaired electrons and therefore, possess a charge of +3. The ordered magnetic moments (2-3 {dollar}musb{lcub}rm B{rcub}{dollar}) are less than the 4 {dollar}musb{lcub}rm B{rcub}{dollar} expected for four unpaired electrons. The magnetic coupling is attributed to interactions between the localized moments and the conduction electrons which is referred to as the Rudderman-Kasuya-Kittel-Yoshida (RKKY) interaction.; Temperature dependent resistivity measurements indicate that (Ca,Sr,Ba){dollar}sb{lcub}14{rcub}{dollar}MnBi{dollar}sb{lcub}11{rcub}{dollar} are metals with a sharp drop in their slopes at the magnetic ordering temperatures. The resistivity curve for Ba{dollar}sb{lcub}14{rcub}{dollar}MnBi{dollar}sb{lcub}11{rcub}{dollar} also displays a minimum in the resistivity curve slightly above the ordering temperature, which si characteristic of the Kondo effect. The Sb compounds display resistivity curves which are intermediate between the metallic Bi compounds and the semiconducting As compounds. The sharp drop in the resistivity curve is also observed in the Sb compounds. The resistivity results agree with the presence of an RKKY interaction.; The synthesis of Ca{dollar}sb{lcub}14{rcub}{dollar}NiBi{dollar}sb{lcub}11{rcub}{dollar}, Ca{dollar}sb3{dollar}MnBi{dollar}sb3{dollar}, Ca{dollar}sb3{dollar}MnBi{dollar}sb3{dollar}, and Ca{dollar}sb9{dollar}Mn{dollar}sb4{dollar}Bi{dollar}sb9{dollar} was also attempted. It appears that new structure types may have been synthesized but X-ray diffraction quality crystals were not obtained.; Neutron diffraction measurements were performed on Sr{dollar}sb{lcub}14{rcub}{dollar}MnBi{dollar}sb{lcub}11{rcub}{dollar}. They indicate that this compound is a normal ferromagnet and not a canted ferromagnet. Although, the magnitude of the ordered Mn moments are not available, the direction of the ordered Mn moments appear to be towards the (1 2 1) direct of the unit cell.; These results are discussed in relation to the bonding within these compounds and to the Zintl concept.