Hydrogen impurity effects.A_5Tt_3Z intermetallic comounds between A=Ca,Sr,Ba,Eu,Yb=and Tt-Sn,Pb with Cr_5B-3-like strucures that are stabilized by hydride or fluoride (Z)

摘要

The binary systems Ca-Sn,Ba-Sn,Eu-Sn,Yb-Sn,Sr-Pb,Ba-Pb,and Eu-Pb do not contain Cr_5B_3-like A_5Tt_3 phases when care is taken toexclude hydrogen from the reactions(Tt=tetrel,Si-Bb).All form ternary A_5Tt_3H_x phases (x<=1) with "stuffed"Cr_5B_3-like structures instead,and all of those tested,Ca-Sn,Ba-Sn,Sr-PB,and Ba-Pb,also yield the isostructural A_5Tt_3F.The structures and compositions of Ca_5Sn_3H_x,Ca_5Sn_3F_(0.89),Eu_5Sn_3H_x,and Sr_5Pb_3F have been refined from single-crystal X-ray diffraction data and of Ca_5Sn_3D from powder neutron data.Teh interstitial H,F atoms are bound in a tetrahedral (A~(2+)_4 cavity in a Cr_5B_3-type metal atom structure.Nine previous reports of binary"Ba_5Sn_3","Yb_5Sn_3",and "Ba_5Pb_3" compounds were wrong and presumable concerned the hydrides.Tehnew 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.Teh Sn-Sn bonds appear correspondingly shortened on oxidation.Other new phases reported are conduction band.The Sn-Sn bonds appear corespondingly shortened on oxidation.Other new phases reported are CaSn(CrB type),Yb_5Sn_4H-x(Sm_5Ge_4),YbSn (approx TlTe0,Ba_5Pb_3(allproxW_5Si_3),and Yb_(31)Pb_(20)(Ca_(31)Sn_(20).