Étude cristallographique de sulfures de terres rares et de sodium

Abstract

On décrit deux catégories de sulfures de terres rares et de sodium. Dans les deux cas, la terre rare T et l'ion Na ont la coordinence six. La première catégorie comprend les terres rares T = La, Ce, Pr, Nd. La structure peut être considérée comme étant du type NaCl, lacunaire et désordonnée. Les anions S forment un paquetage cubique compact tandis que les cations occupent au hasard les sites des Na de la même façon que dans BiNaS₂. A la deuxième catégorie, appartiennent les terres rares T = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er et Y. La structure est rhomboédriquement déformée, mais encore apparentée au type NaCl. Le groupe d'espace est R ˗3m˗ (D⁵3d). Dans le paquetage compact, presque cubique des anions S en 6c) les cations T occupent les sites 3a) et les cations Na les sites 3 b), formant ainsi un type de structure de formule TNaS₂ analogue à celle de CrNaS₂.

Electronic Structure, Elastic and Optical Properties of AEuS2 (A = Na, K, Rb, and Cs) Ternary Sulfides: First‐Principles Study

“…Because the lattice parameter c characterizes the distance between the parallel layers that varies with the ionic alkali metal radius, the variation of c is larger than the variation of a when going from NaEuS 2 to CsEuS 2 (see Table ). This trend was also noted in other compounds similar to the studied compounds: a (NaLaSe2) = 4.34 Å, a (KLaSe2) = 4.40 Å, a (RbLaSe2) = 4.43 Å; c (NaLaSe2) = 20.79 Å, c (KaLaSe2) = 22.78 Å, c (RbaLaSe2) = 23.71 Å . The results are in line if we take into account the difference of ionic radius: R (Na + ) = 1.09 Å < R (K + ) = 1.38 Å < R (Rb + ) = 1.54 Å < R (Cs + ) = 1.72 Å .…”

“…This feature gives the possibility of studying the changes in physical and chemical properties of these compounds across the alkali metals series. Thier structures have been completely determined …”

ALnS 2 :RE (A=K, Rb; Ln=La, Gd, Lu, Y): New optical materials family

“…The unit cell symmetry operations in the R3m space group produce other symmetrically equivalent locations of these atoms [47]. In the literature, the swapped cation positions (Ln 3+ at 3a, A + at 3b) are common as well [48] -in this case, the reported z' for sulfur at the 6c site (0,0,z') is related to z by z = ½ -z'. All atoms in this structure have a coordination number 6 -both A and Ln are surrounded by six sulfur atoms (AS 6 and LnS 6 octahedra, see figure 1), while sulfur is surrounded by three A and three Ln atoms.…”

Na2ZrS3: Ein ternäres Sulfid des Zirconiums mit aufgefüllter AlCl3-Struktur

“…Na + kann dabei durch den Einbau in ein terna È res sulfidisches Nebenprodukt der Zusammensetzung NaMS 2 (M = La±Lu) abgefangen werden. Findet man fu È r M = La±Sm [2] noch eine ungeordnete Steinsalzstruktur mit einer Na + /M 3+ -Statistik auf der Kationenlage vor, so wird fu È r M = Eu±Lu [3] eine Ausordnung der Kationen im Sinne der α-NaFeO 2 -Struktur [4] realisiert. Versucht man diese pra È parativen Erkenntnisse auch auf die Kristallchemie des Zirconiums zu u È bertragen, so erha Èlt man, neben einem nitridhaltigen Hauptprodukt der Zusammensetzung NaZr 2 N 2 SCl [5] (isotyp mit z.…”