YIH n : A New Family of Metal‐rich Hydride Halides

The graphite‐like yttrium hydride halides, YIH n (0.8 ⩽ n ⩽ 1.0), have been prepared in quantitative yields by heating either YI 3 , YH 2 (1:2) or stoichiometric YI 3 , YH 2 , Y mixtures in sealed Ta ampoules at 900°C. A lower limit of the homogeneity range, n ≈ 2/3, has been determined from dehydrogenation experiments. All YIH n phases adopt the ZrBr‐type heavy‐atom structure. The hydrogen variation is accompanied by a change in the c lattice constant from 31.162(3) to 31.033(1) Å for n = 0.61(3) to 1.02(3). The YIH n phases reversibly react with hydrogen at 400‐600°C to form the light green transparent compound YIH 2 . However, increasing the reaction temperature above 700°C causes decomposition to an unidentified phase being in equilibrium with YH 2 and YI 3 . The arrangement of the heavy atoms in YIH 2 ( P $\bar 3$ m 1; a = 3.8579(3) Å, c = 10.997(1) Å) corresponds to a four‐layer I‐Y‐Y‐I slab with the stacking sequence (AbaB) as was found by x‐ray powder diffraction data refinement with the Rietveld method. A miscibility gap exists between YIH and YIH 2 . Samples YIH n ( n ⩽ 1.0) show metallic conductivity at room temperature, which changes into semiconducting behavior with decreasing temperature as n approaches its lower value ≈ 2/3.