Intermetallic Compounds with Near Zintl Phase Behavior:  RE₂Zn₃Ge₆ (RE = La, Ce, Pr, Nd) Grown from Liquid Indium

Abstract

A series of compounds has been discovered while investigating reactions of rare earth, transition metals, and Ge in excess indium. These compounds, RE2Zn3Ge6 (RE = La, Ce, Pr, Nd), are isostructural, crystallizing in the orthorhombic space group Cmcm with lattice parameters a = 5.9691(9) angstroms, b = 24.987(4) angstroms, and c = 5.9575(9) angstroms for La2Zn3Ge6, a = 5.9503(5) angstroms, b = 24.761(2) angstroms, and c = 5.9477(5) angstroms for the Ce analogue, a =5.938(2) angstroms, b = 24.708(8) angstroms, and c = 5.936(2) angstroms for Pr2Zn3Ge6, and a = 5.9094(7) angstroms, b = 24.619(3) angstroms, and c = 5.9063(5) angstroms for the Nd analogue. The structure is composed of PbO-like ZnGe layers and ZnGe4 cage layers and is related to the Ce4Zn8Ge(11-x) structure type. The bonding in the system can be rationalized using the Zintl concept resulting in a material that is expected to be a valence precise semiconductor, although its behavior is more consistent with it being a semimetal, making it an intermediate case. The results of band structure calculations and magnetic measurements of these compounds are discussed.

Eleven new compounds in the RE–Cd–Ge systems (RE=Pr, Nd, Sm, Gd–Yb; Y): Crystal chemistry of the RE2CdGe2 series

“…Some examples include REZnGe (YPtAs structure type) [31], RE 2 Zn 15 Ge 2 (Th 2 Zn 17 structure type) [32], RE 2 Zn 6 Ge 3 [33], RE 2 Zn 3 Ge 6 [34], and RE 4 Zn 5 Ge 6 [35]. The latter three series crystallize in own structure types.…”

SrZn2Sn2 and Ca2Zn3Sn6 — two new Ae–Zn–Sn polar intermetallic compounds (Ae: alkaline earth metal)

“…63), with lattice constants a ¼6.340(1)Å, b¼26.782(2)Å, c¼ 6.333(1)Å. The phase is isotypic to the R 2 Zn 3 Ge 6 (R ¼La, Ce, Pr, Nd) compounds [41]. As for SrZn 2 Sn 2 , the Zn-Sn structure part can be described as built of two types of layers which are alternatingly stacked and …”

“…Ca 2 Zn 3 Sn 6 is isotypic to the R 2 Zn 3 Ge 6 (R¼La, Ce, Pr, Nd) compounds [41], indicating that this structure type can also accommodate different electron counts. The R 2 Zn 3 Ge 6 compounds with R 3 þ rare earth ions have been described as ''intermetallic compounds with near Zintl phase behavior'': Assuming R 3 þ and Zn 2 þ cations, (3b-Ge À ) atoms in {Ge 4 Zn} layers since they each participate in three Ge-Ge bonds, and (0b-Ge 4 À ) atoms in {ZnGe 4/4 } layers because they are not involved in Ge-Ge bonds, leads to the charge balanced formulation (R 3 þ ) 2 (Zn 2 þ ) 3 (3b-Ge À ) 4 (0b-Ge 4 À ) 2 , while DFT calculations (for La 2 Zn 3 Ge 6 ) show a non-zero but low DOS at the Fermi level, indicating that the phases are (semi)metallic, and also experimental tests for each of the R 2 Zn 3 Ge 6 phases did not show band gaps [41].…”

The new series of RZnGe compounds (R=rare earth element) with the YPtAs structure type

“…In particular, the following phases are known: EuZnGe and YbZnGe (ZrBeSi and CeCu 2 type, respectively) [4,5]; YbZn 2 Ge 2 (BaAl 4 type) [6]; EuZn 2 Ge 2 , reported with both the CaBe 2 Ge 2 structure [7] and the ThCr 2 Si 2 type [8]; R 2 Zn 6 Ge 3 with R ¼ La, Ce, Pr, Sm, Gd (Ce 2 Zn 6 Ge 3 type) [9]; R 4 Zn 5 Ge 6 with R ¼ Gd, Tm and Lu [10] and Tb 4 Zn 5 Ge 6 [11] (Gd 4 Zn 5 Ge 6 type), R 4 Zn 8 Ge w10 with R ¼ Ce, Nd, Gd (Ce 4 Zn 8 Ge 11Àx type) [12]; R 2 Zn 15 Ge 2 with R ¼ Ce, Nd (Th 2 Zn 17 type) [13,14]; RZn 1.5 Ge 0.5 (R ¼ La-Sm), belonging to the AlB 2 type (or some AlB 2 derivative) [15], La 5 ZnGe 3 (La 5 CrGe 3 type) [16]. More recently, the crystal structure of the novel ytterbium zinc germanide (Yb 2 Zn 3 Ge 3.1 ) [17] and of the Re 2 Zn 3 Ge 6 compounds (Re ¼ La, Ce, Pr, Nd [18]) have been also elucidated.…”