Hydrogen impurity effects. A(5)Tt(3)Z intermetallic compounds between A = Ca, Sr, Ba, Eu, Yb and Tt = Sn, Pb with Cr(5)B(3)-like structures that are stabilized by hydride or fluoride (Z).

Abstract

The binary systems Ca-Sn, Ba-Sn, Eu-Sn, Yb-Sn, Sr-Pb, Ba-Pb, and Eu-Pb do not contain Cr(5)B(3)-like A(5)Tt(3) phases when care is taken to exclude hydrogen from the reactions (Tt = tetrel, Si-Pb). All form ternary A(5)Tt(3)H(x)() phases (x < or = 1) with "stuffed" Cr(5)B(3)-like structures instead, and all of those tested, Ca-Sn, Ba-Sn, Sr-Pb, and Ba-Pb, also yield the isostructural A(5)Tt(3)F. The structures and compositions of Ca(5)Sn(3)H(x), Ca(5)Sn(3)F(0.89), Eu(5)Sn(3)H(x), and Sr(5)Pb(3)F have been refined from single-crystal X-ray diffraction data and of Ca(5)Sn(3)D from powder neutron data. The interstitial H, F atoms are bound in a tetrahedral (A(2+))(4) cavity in a Cr(5)B(3)-type metal atom structure. Nine previous reports of binary "Ba(5)Sn(3)", "Yb(5)Sn(3)", "Sr(5)Pb(3)", and "Ba(5)Pb(3)" compounds were wrong and presumably concerned the hydrides. The new ternary phases are generally Pauli-paramagnetic, evidently with pi electrons from the characteristic tetrelide dimers in this structure type at least partially delocalized into the conduction band. The Sn-Sn bonds appear correspondingly shortened on oxidation. Other new phases reported are CaSn (CrB type), Yb(5)Sn(4)H(x) (Sm(5)Ge(4)), YbSn ( approximately TlTe), Ba(5)Pb(3) ( approximately W(5)Si(3)), and Yb(31)Pb(20) (Ca(31)Sn(20)).