Hexapraseodymium heptanickel tetrasilicide, Pr6Ni7Si4, an intergrowth of ThSi2- and Y3Rh2Si2-type slabs

Abstract

Abstract. Mr= 1368.76, oP68, orthorhombic, Pbcm, a = 5.888 (1), b = 7.4265 (9), c = 29.558 (8) A, V= 1292.6 (2) A 3, Z=4, D x=7.033gcm -3, MoK~t, 2 = 0.7107 A, g = 32.24 mm -~, F(000) = 2424, room temperature, final R =0.026 for I011 contributing reflections. The Pr6Ni7Si 4 structure can be consideredSi (1) 8 (e) as an intergrowth of ThSi z-and Y3Rh2Si2-type slabs. It Pr(l) 8(e) is built up exclusively of trigonal prisms formed by Pr Ni(l) 8(e) atoms and centered by Ni or Si atoms. Apart from the Ni(2) 8(e)Si (2) 8(e) central part of the ThSi 2 slab, the structure obeys the Pr(2) 8(e) waist-contact restriction rule. Ce6Ni7Si 4 [a = 5.942 (2), Ni(3) 8 ( with Pr6NivSi 4.

Preparation, Crystal Structure, and Physical Properties of the Rare-Earth Metal Palladium Silicides LnPdSi (Ln = La, Ce, Pr) and the a-ThSi2 Type Compounds LaPd0.787(2)Si1.213(2) and CePd0.758(5)Si1.242(5)

“…The two-dimensionally infinite cutout of puckered 4-and 8-membered rings shown in D of Fig. 4 is also found in the EuNiGe type structure of the compounds EuPdGe [17] and CaPdSi [18], as well as in Pr 6 Ni 7 Si 4 [19], in Ce 3 Rh 3 Si 2 [20], and in the Nd 4 Rh 4 Ge 3 type palladium silicides Ca 4 Pd 4 Si 3 [21] and Sm 4 Pd 4 Si 3 [22]. In BaPdP [23] this net with the Schla È fli symbol 4.8 2 [24] is found in planar form.…”

The Ce–Ni–Si System Revisited: More Homologue Compounds?

“…Thus, one must explore the lower-temperature region to inspect the formation of those phases. For example, La 3 Ni 4 Si 2 was reported to be stable below 750 °C while single crystals of Ce 3 Ni 4 Si 2 and RE 6 Ni 7 Si 4 were obtained at 800 °C or higher . Preference of formation with specific RE atoms can be seen from the fact that there are no reported isotypic RE 3 Ni 4 Si 2 compounds with RE atoms other than La and Ce.…”

“…Search for binary and ternary Ce−Ni-containing compounds with such interatomic distances in Pearson's Crystal Data 6 resulted in 33 entries, one of which, Ce 6 Ni 7 Si 4 is a neighboring phase in the Ce−Ni−Si system. Ce 6 Ni 7 Si 4 crystallizes in a primitive orthorhombic unit cell, isotypic with Pr 6 Ni 7 Si 4 with a unit cell volume of 1.29231 nm 3,11 , which is almost twice as big than that of Ce (see Figure 10). The removal of the nickel chain, which corresponds to half a Ni atom per formula unit of Ce 3 Ni 4 Si 2 (5.56 at.…”

Four ternary silicides in the La–Ni–Si system: from polyanionic layers to frameworks

“…Both of them crystallize in the orthorhombic system with the space groups Pnma ( oP 32) and Pbcm ( oP 68), respectively, and show complex polyanionic nets. La 3 Ni 3 Si 2 belongs to the Ce 3 Rh 3 Si 2 structure type, 35 while La 6 Ni 7 Si 4 to Pr 6 Ni 7 Si 4 , 21 both being quite underrepresented.…”

“…La 6 Ni 7 Si 4 and La 3 Ni 3 Si 2 instead are characterized by polyanionic networks. The former one belongs to the Pr 6 Ni 7 Si 4 structure type with Ce and Nd homologues reported as other representatives, 21 while the latter has been observed only with Rh and Ir. 2 The investigation has been performed employing X-ray diffraction, microscopy analysis and first-principle calculations.…”