Phase equilibria in the La-Mg-Ge system at 500 degrees C and crystal structure of the new ternary compounds La11Mg2Ge7 and LaMg3-xGe2

作者：De Negri S^*; Solokha P; Skrobanska M; Proserpio D M; Saccone A

来源：Journal of Solid State Chemistry, 2014, 218: 184-195.

DOI：10.1016/j.jssc.2014.06.036

• Germanides
• Phase equilibria
• Crystal structure
• Single-crystal X-ray diffraction
• Group-subgroup relation

The whole 500 degrees C isothermal section of the La-Mg-Ge ternary system was constructed. The existence and crystal structure of three ternary compounds were confirmed: La2+xMg1-xGe2 (tau(2), P4Imbm, tP10-Mo2FeB2, 0 <= x <= 0.25), La4Mg5Ge6 (tau(3), Cmc2(1), oS60-Gd4Zn5Ge6) and La4Mg7Ge6 (tau(4), C2/m, mS34, own structure type). Five novel compounds were identified and structurally characterized: La11Mg2Ge7 (tau(1), P4(2)/ncm, tP88-8, own structure type, a=1.21338(5), c=1.57802(6) nm), LaMg3-xGe2 (tau(5), P<(3)over bar1c> hP34-0.44, own structure type, x=0.407(5), a=0.78408(4), c=1.45257(7) nm), La6Mg23Ge (tau(6), <fm(3)over barm>, cF120-Zr6Zn23Si, a=1.46694(6) nm), La4MgGe10-x (tau(7), x=0.37(1), C2/m, mS60-1.46, own structure type, a=0.88403(8), b=0.86756(8), c=1.7709(2) nm,) beta=97.16 degrees(1) and La2MgGe6 (tau(8), Cmce, oS72-Ce-2(Ga0.1Ge0.9)(7), a=0.8989(2), b=0.8517(2), c=2.1064(3) nm). Disordering phenomena were revealed in several La-Mg-Ge phases in terms of partially occupied sites. The crystal structures of La11Mg2Ge7 and LaMg3-xGe2 are discussed in details. The latter is a root 3a x root 3a x 2c superstructure of the LaLi3Sb2 structure type; the symmetry reduction scheme is shown in the Barnighausen formalism terms. 0 2014 Elsevier Inc.

• 出版日期2014-10