Lukachuk Mar'yana, Kremer Reinhard K, Mattausch Hansjürgen, Simon Arndt
Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
Inorg Chem. 2007 Apr 16;46(8):3231-5. doi: 10.1021/ic062425d. Epub 2007 Mar 21.
The title compounds were synthesized from RE, REX3, and Ge under an Ar atmosphere at 1200-1370 K. Y2GeI2 and Gd2GeI2 crystallize in space group Rm with lattice constants a = 4.2135(3) and 4.2527(1) A and c = 31.480(2) and 31.657(1) A, respectively. Gd2GeBr2 crystallizes in two modifications, the 1T-type (space group Pm1; a = 4.1668(2) A, c = 9.8173(6) A) and the 3R-type (space group Rm; a = 4.1442(9) A, c = 29.487(7) A). The structural motifs of RE2GeX2 compounds are Ge-centered slightly distorted RE6 octahedra connected via their common edges and extending in the a and b directions. The resulting close-packed double layers are separated by halogen atoms. The electrical resistivity measurements revealed semiconductor behavior for Y2GeI2 and Gd2GeI2 and a metal-semiconductor transition for 1T-Gd2GeBr2. Magnetic susceptibility and heat capacity measurements show long-range magnetic ordering for Gd2GeI2 and 1T-Gd2GeBr2 at approximately 15 and approximately 13 K, respectively.
标题化合物是在氩气气氛下，于1200 - 1370 K温度下由稀土元素（RE）、REX₃和锗合成的。Y₂GeI₂和Gd₂GeI₂分别以空间群Rm结晶，晶格常数a = 4.2135(3) Å和4.2527(1) Å，c = 31.480(2) Å和31.657(1) Å。Gd₂GeBr₂有两种变体结晶，1T型（空间群Pm1；a = 4.1668(2) Å，c = 9.8173(6) Å）和3R型（空间群Rm；a = 4.1442(9) Å，c = 29.487(7) Å）。RE₂GeX₂化合物的结构单元是以锗为中心的略微扭曲的RE₆八面体，它们通过公共边相连并在a和b方向上延伸。由此形成的密堆积双层被卤素原子隔开。电阻率测量表明Y₂GeI₂和Gd₂GeI₂具有半导体行为，而1T - Gd₂GeBr₂具有金属 - 半导体转变。磁化率和热容测量表明，Gd₂GeI₂和1T - Gd₂GeBr₂分别在约15 K和约13 K时出现长程磁有序。
