COMPOUNDS OF ALKALINE-EARTH AND DIVALENT RARE-EARTH-METALS STABILIZED BY HYDROGEN IMPURITIES - THE YB5SB3 AND MN5SI3 STRUCTURE TYPES FOR PNICTIDES

All eight reported examples of the orthorhombic (beta-)Yb5Sb3-type structure are ternary hydrides, namely, A5(Sb,Bi)3H for A=Ca, Sr, Eu, Yb. One additional example is Sm5Bi3H. These may be obtained in quantitative yields through the inclusion of AH2 in the syntheses. On the contrary, heating these products or the elementary reactants at 900-1100-degrees-C in high vacuum while sealed in Ta regularly affords only hexagonal Mn5Si3-type products, i.e., A5Pn3 for A=Ca, Sr, Ba, Sm, Eu or Yb, Pn=As, Sb or Bi, except for As with Ba or Sm. The examples with Ca5Bi3, Eu5(Sb,Bi)3 and Yb5Bi3 are new. Several problems with supposedly dimorphic phases are thus clarified. The hydrogen content of the typical sublimed or distilled alkaline-earth metals is often particularly serious (approximately 6-20 at.% H). The A5Pn3 phases with either structure type take up variable amounts of hydrogen and thereby exhibit significant variations in their individual lattice constants.