High-pressure synthesis of rare-earth metal disulfidesand diselenides LnX ₂ (Ln = Sm, Gd, Tb, Dy, Ho, Er and Tm; X = S, Se)

Abstract

A series of rare-earth metal disulfides LnS 2 and diselenides LnSe 2 (Ln ¼ Sm, Gd, Tb, Dy, Ho, Er and Tm) has been prepared by high-pressure high-temperature synthesis at 8(1) GPa. The dichalcogenides LnX 2 (X ¼ S, Se) are found to crystallize in the a-LaS 2 type with the monoclinic space group P12 1 /a1 (no. 14). The crystal structure is a twofold superstructure of the ZrSSi aristotype and consists of puckered cationic [LnX] þ double slabs which are sandwiched by planar chalcogen sheets containing X 2À 2 dumbbells.

Rare Earth Metal PolytelluridesRETe1.8(RE= Gd, Tb, Dy) – Directed Synthesis, Crystal and Electronic Structures, and Bonding Features

“…Although CeTe 2 and PrTe 2 crystallize isotypically, the interatomic differences in the Te layers differ from each other, especially for the Te 4 squares at z ≈ 1/2 , . This is in remarkable contrast to the disulfides and diselenides REX 2 , where the planar chalcogenide layers contain only dinuclear X 2 2– dumbbells . Tellurium seems more prone to distribute the anionic charges over larger units, which is not only observed in rare earth metal compounds …”

Transport Properties of GdTe1.8–xAsx (x = 0, 0.04)

“…This results in shorter interatomic distances in the X 2 2– anions and larger distances between them. The sulfides and selenides have been intensively investigated, for example high‐temperature high‐pressure experiments have been employed to reach pressure stabilized phases of the smaller rare earth metals in REX 2 ( RE = Sm, Gd–Tm, X = S, Se) and REX 1.9 ( RE = Gd–Tm, X = S, Se) . The corresponding tellurides have been investigated less and the reported structures of the stoichiometric RE Te 2 ( RE = La, Ce, Pr) compounds differ from those of the analogous rare‐earth metal sulfides and selenides,, , although CeTe 1.9 crystallizes in the CeSe 1.9 structure type that is common to the corresponding sulfides and selenides …”

Microwave‐Assisted Synthesis, Characterization, and Thermal Decomposition of Rare‐Earth Metal Disulfides RES2 (RE = La, Pr, Nd)

“…Polysulfides RE S 2– δ ( RE = Y, La–Nd, Sm, Gd–Lu; 0 ≤ δ < 0.3) of trivalent rare‐earth metals have been intensively studied in the last years with focus on synthesis, crystal structures, thermal properties, and thermodynamic data 1–7. The structures of these compounds generally consist of puckered [ RE S] + double slabs and planar [S] 1– δ layers and can be related to the tetragonal ZrSSi type ( P 4/ nmm , a 0 ≈ 3.8 Å, c 0 ≈ 8 Å8).…”

“…The planar sulfide layers in the rare‐earth metal disulfides RE S 2 consists of S$\rm^{2&#x02013;}_{2}$ dinuclear anions arranged in a herringbone‐like pattern. Two polymorphs are known for these disulfides: The monoclinic α‐ RE S 2 type (space group P 2 1 / a , lattice parameters a ≈ 8 Å, b ≈ 4 Å, c ≈ 8 Å, β ≈ 90°)3,5,7,9 and the orthorhombic β‐type ( Pnma ; a ≈ 8 Å, b ≈ 16 Å, c ≈ 3 Å) 3,10. The chalcogen layers of the compounds RE S 2– δ with δ > 0 exhibit defects and isolated S 2– anions besides dinuclear S$\rm^{2&#x02013;}_{2}$ anions.…”

“…To prepare stoichiometric disulfides of the lighter rare‐earth metals and to overcome the increasing decomposition pressure, two general approaches seem possible: the application of high‐pressure synthesis conditions or a considerable reduction of the reaction temperature. The first possibility has recently proven its capability again 5,7. The general obstacle for the low‐temperature routes is the allocation of a sufficient amount of activation energy.…”