Gd 3 Ru 4+x All2-x [x = 0.13 (2)], Mr = 1209.44, hexagonal, hP38, P6 3 /mmc – kh 2 g f ba (No. 194), a = 8.8142 (6), c = 9.5692 (9) A, V= 643.8 (1) A 3 , Z = 2, D x =6.239Mgm -3 , A(Mo Ka)=0.71073A, u= 20.330 mm -1 , F(000) = 1056 (1), T= 293 K, wR=0.023 for 338 contributing unique reflections. Gd 3 Ru 4 AI 12 is a substitution variant of the Sc 3 Ni 11Ge 4 structure which is a partly disordered variant of the Sc 3 Ni 11 Si 4 type, all three structures being ternary substitution derivatives of the EuMg 5.2 or ErZn 5 types. Contrary to the related structure types, in Gd 3 Ru 4 AI 12 both Wyckoff sites 2(a) and 2(b) have full occupation, i.e. an ordered arrange- ment of alternate Ru and AI atoms is observed along the c axis. The structure of Gd 3 Ru 4 AI 12 is built up of two kinds of layers perpendicular to [001]: planar layers of composition Gd 3 Al 4 and puckered layers of composition Ru 4 AI 5 . Similar layers are found in cubic Hf 6 Ni 7 AI 16 , a ternary substitution variant of Th 6 Mn 23 , as well as in hexagonal Sr 9 Mg 38 and BaLi 4 .
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Gladyshevskii et al. (1993) studied this question.