Preparation and Structures of Lanthanoid Germanides, PrGe3.36, NdGe3.25, and TmGe3 with Double Square Ge-Mesh Structures

Abstract

A series of lanthanoid trigermanides of Pr, Nd, and Tm has been prepared by high-pressure (35 GPa) and hightemperature (1200°C) reactions. TmGe 3 crystallizes in an orthorhombic unit cell (Cmcm, No. 63) with a = 3.990(1) ¡, b = 20.488(5) ¡, c = 3.8794(8) ¡, and V = 317.2(1) ¡ 3. It is isotypic with the DyGe 3 structure composed of Ge zig-zag chains and Tm situated between double square Ge-meshes. PrGe 3.36 crystallizes in an orthorhombic unit cell (Cmmm, No. 65) with a = 4.062(4) ¡, b = 21.43(3) ¡, c = 4.212(6) ¡, and V = 366.6(8) ¡ 3 . The structure is principally the same to the DyGe 3 structure but contains an additional Ge site. The site is partially occupied, and is situated on the square mesh. Each Ge atom in the site is coordinated by five Ge atoms in the chain and in the mesh. , Tb 3+ , and Gd 3+ form the DyGe 3 structure. 16 The structure contains two types of Ge subunits as shown in Figure 1.1 One is a zig-zag chain and the other is a layer composed of double square meshes. Dy ions and the Ge chains are situated between the layers. The space group is Cmcm and the double meshes are stacked along the b axis. The chains extend along the c axis corresponding to the diagonal direction of the meshes. The lattice constants of the a (4.0278(5) ¡) and c (3.8997(5) ¡) axes of DyGe 3 are very similar but not the same, because the mesh is slightly distorted from the regular square net.Light lanthanoid elements do not form the DyGe 3 structure. For these elements, only the compounds with compositions of LnGe x with x¯2 have been reported by reactions under ambient pressure. However, in our recent studies, Ge rich compounds were obtained by high-pressure and high-temperature reactions, such as LnGe 5 , Ln = La, Ce, Pr, Nd, and Sm with the LaGe 5 structure, and CeGe 3 with the Cu 3 Au structure. 79 The former has a tunnel structure composed of GeGe covalent network containing uncommon 8-coordinated Ge atoms.We are interested in the structures of Ge networks in lanthanoid germanides formed under high pressure. In the present study, we have investigated the reactions of Pr, Nd, and Tm with Ge and successfully prepared three new germanides PrGe 3.36 , NdGe 3.25 , and TmGe 3 with the aid of high-pressure and high-temperature conditions. They have the DyGe 3 structure (for Tm), and its closely related structures (for Pr and Nd). ExperimentalThe new lanthanoid germanides were prepared as follows: Pr (Nilaco 99.9%) and Tm (Nilaco 99.7%) were reacted with Ge (Mitsuwa Pure Chemical 99.999%) in a molar ratio of 1:3 in an arc Figure 1. The crystal structure of DyGe 3 . The yellow and green balls represent Dy and Ge atoms, respectively. It has a layer structure composed of Dy 3+ ions, double square Ge-meshes, and Ge-chains.

High-pressure synthesis of SmGe3

“…Within the series of rare earth metal trigermanides MGe 3 (M = La, Ce, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) [12][13][14][15][16][17][18][19][20][21][22] and their variants MGe 3−x (M = Tb, Dy, Yb) [34,35] and MGe 3+x (M = Nd, Pr) [21], different structural motifs are observed. The overview (Figure 9) illustrates that the selected parameters do not allow for a clear separation, but Figure 7: Group-subgroup schemes for the structures of htand lt-Cu 3 Au [43,33], CuPt 7 [44,45], SrPb 3 [46] and SmGe 3 .…”

Stabilization of CeGe$_3$ with Ti and O featuring tetravalent Ce ions: (Ce$_{0.85}$Ti$_{0.15}$)Ge$_3$O$_{0.5}$

“…The specific atomic volume per atom of the title compound is 18.52 A 3 (20.83 A 3 if ignore oxygen), smaller than 21.78 A 3 , 20.89 A 3 and 21.36 A 3 for the high pressure phase of LaGe 3 , PrGe 3 and NdGe 3 prepared under similar pressure conditions ( 3 ∼ 12 GPa, 500 ∼ 1200 °C), respectively [19,20]. The value for high pressure CeGe 3 is 20.64 A 3 , and for high pressure SmGe 3 is 20.38 A 3 .…”

“…For larger rare earth elements, RGe 3 phases mostly form in an orthorhombic structure, and some of them are reported only from high pressure synthesis. LaGe 3 [19], PrGe 3.36 and NdGe 3.25 [20] do not adopt Cu 3 Au type but hp-CeGe 3 does [17]. That is probably because of the smaller compressibility of the La, Pr and Nd compared with Ce atoms, due to the lack of valence change.…”

“…The high pressure and high temperature synthesis (3 ∼ 12 GPa, 500 ∼ 1200 °C) of LaGe 3 lead to the formation of a compound with a BaPb 3 -type instead of Cu 3 Au-type structure [19] with specific atomic volume of 21.78 A 3 , larger than hp-CeGe 3 . PrGe 3 and NdGe 3 form a new type of structure [20] with specific atomic volume 20.89 A 3 and 21.36 A 3 respectively, also larger than hp-CeGe 3 . The superconducting compounds of LaSn 3 and LaPb 3 were found to crystallize in the Cu 3 Au-type structure, similar to CeSn 3 and CePb 3 [21][22][23][24].…”

High-Pressure Synthesis and Chemical Bonding of Barium Trisilicide BaSi3

“…A systematic study of tetrel connectivities in polyanions revealed a variety of motifs with composition MT 3 ( M = Ca, Sr, Ba, Y, La, Ce, Eu, Gd, Tb, Ho, Er, Tm, Yb, Lu; T = Si, Ge) [8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]. All of these exceed the scope of the 8- N rule and show interesting physical properties such as superconductivity.…”