Symmetrieverwandtschaften bei Varianten des Perowskit-Typs

Abstract

The relationships among the huge number of derivative structures of the perovskite type are rationalized in a concise manner using group-subgroup relations between space groups. One family tree of such relations is given for perovskites having tilted coordination octahedra. Further group-subgroup relations are concerned with distortions of the octahedra, such as Jahn-Teller distortions or with atoms shifted from the octahedron centres. In these cases, the space-group symmetry reductions must allow site symmetry reductions of the occupied sites in the perovskite structure. On the other hand, subgroups in which the perovskite sites split into different independent sites are necessary for derivative structures with atom substitutions, such as in the elpasolites A(2)EMX(6). In addition, substitutions and distortions can be combined in adequate subgroups. Substitutions may also involve the occupation of atom sites of perovskite by molecular groups such as N(CH(3))(4)(+) or other organic cations, or by molecules like acetonitrile. If they are ordered, their molecular symmetry requires further space-group symmetry reductions. The anions can be replaced by cyanide ions or by NO(2)(-) ions; space-group symmetry then depends on the temperature-dependent degree of order. The relationships can be used to predict if and what kind of twinning may occur in phase transitions and whether second-order phase transitions are possible.

Synthesis, crystal structure and magnetism of the mixed metal hydrides Eu1−xSrxMg2H6 (0≤x≤0.6)

“…A notable exception to this structure analogy is EuMg 2 H 6 [8] for which no strontium or other alkaline earth analogue has been found so far. The structure of this hydride is unique in the sense that it shows a novel vacancy derivative of the cubic perovskite type [8] in spite of the plethora of oxide and fluoride perovskite type variants already known [14,15]. Furthermore, its magnesium-deuterium distance of 177 pm is the shortest one ever reported in a metal hydride [8].…”

Ln3[SiON3]O (Ln = La, Ce, Pr) – Three Oxonitridosilicate Oxides with Crystal Structures Derived from the Anti‐Perovskite Structure Type

“…Supporting Information: Anisotropic displacement parameters for the three compounds 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Ln (2)-N/O(1) [1] (4x) 2.734(5) 2.712(4) 2.699 (3) Si (1)-N/O(1) [1] (4x) 1.728 (6) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 …”

“…Oxonitridosilicates are intermediates between classical oxosilicates and nitridosilicates and can be formally derived by partial substitution of O for N. While oxygen in classical oxosilicates usually occur in a terminal O [1] or simply bridging O [2] function, nitrogen atoms can additionally act as a triply (N [3] ) or even quadruply (N [4] ) bridging atom, leading to a manifold of additional structural possibilities. Consequently, nitridosilicates exhibit a more variable degree of condensation in the range 1 : 4 ≤ κ ≤ 3 : 4 (i.e.…”

“…[1] In this context, the oxonitridosilicate oxide Gd 3 [SiON 3 ]O [2] has been investigated which is isotypic to Ba 3 [SiO 4 ]O [3,4] and Cs 3 [CoCl 4 ]Cl. [5] All three compounds can be derived from the anti-perovskite structure type in a hierarchical sense with tetrahedral building blocks (SiON 3 , SiO 4 , CoCl 4 ) substituting the large alkaline earth ions in perovskite.…”

PbO / PbF2 Flux Growth of YScO3 and LaScO3 Single Crystals – Structure and Solid-State NMR Spectroscopy

“…The four longer Y-O and La-O distances are all above 335 pm. A compact and concise overview on the many distortion variants within the family of perovskite-related structures is given in [33,34].…”