The Intermetallic Zirconium Compounds ZrNiAl, ZrRhSn, and ZrPtGa - Structural Distortions and Metal-Metal Bonding in Fe₂P Related Compounds

Abstract

Intermetallic Compounds, Crystal Structure, Superstructure, Chemical Bonding ZrNiAl, ZrPtGa, and ZrRhSn have been prepared by reacting the elements in an arc-melting furnace and subsequent annealing at 970 K. These compounds have previously been investigated only by use of X-ray powder data for ZrPtGa and ZrRhSn and single crystal film data for ZrNiAl. Precise single crystal diffractometer data are reported in the present paper. The structure of ZrNiAl is confirmed. It adopts a substitution variant of the FeiP type: P62m, a = 691.5(2), c = 346.6(1) pm, Z = 3, wR2 = 0.0538, 320 F2 values, 14 parameters. The structure refinement reveals a large displacement parameter U 33 for one nickel position, indicative of a slight nickel dislocation. Weak superstructure reflections could be found on Guinier powder patterns for ZrPtGa and ZrRhSn. These compounds crystallize with the HfRhSn type structure (Z = 6 , space group P62c), a superstructure of the Fe2P type: a = 714.5(1), c = 706.3(2) pm, w/?2 = 0.0651, 594 F2 values, 18 parameters for ZrPtGa and a = 734.2(2), c = 721.8(2) pm, wR2 = 0.0349, 355 F2 values, 18 parameters for ZrRhSn. Structural motifs of these compounds are transition metal centered trigonal prisms formed by the zirconium, aluminium, gallium, and tin atoms. While these trigonal prisms are regular in ZrNiAl, significant distortions occur in the structures of ZrPtGa and ZrRhSn. Due to the distortions of the trigonal prisms in the superstructures, some platinum and rhodium atoms are dislocated from the subcell mirror planes towards Pt-Pt and Rh-Rh pairs with distances o f 310 and 313 pm, respectively. The formation of the superstructure is most likely due to packing reasons. Chemical bonding in ZrRhSn was investigated on the basis of an extended Hückel calculation.

Structure and Properties of Dimorphic CePdZn

“…The isotypy of α-CePdZn with the hexagonal ZrNiAl type [27] and β-CePdZn with the orthorhombic TiNiSi type [28] was already evident from the Guinier powder data.…”

“…So far, only X-ray powder data have been reported for the hexagonal modification by Iandelli [11]. The corresponding structure types ZrNiAl [27] for α-CePdZn and TiNiSi [28] for β-CePdZn have repeatedly been discussed in literature [32][33][34][35][36][37][38]. For further details we refer to these overviews and 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 the recent work on dimorphic CePtSn [2] and YbPdSn [39,40].…”

Crystal structures of titanium palladium germanium, TiPdGe, two polymorphic modifications

“…TiPdGeexhibits temperature polymorphism adopting the ZrNiAl [1,2] or TiNiSi[3] structure type for the high-(ht) and the lowtemperature (lt) modification, respectively. Due to the very narrow temperature interval in which ht-TiPdGeisstable (transition temperature~1240°C,melting point~1280°C)weare not successful to synthesize the high temperaturemodification as pure bulk material.…”

Crystal structure of hafnium palladium gallium, HfPdGa

“…The new ternary equiatomic compound HfPdGaisisostructural with HfRhSn[2] which represents adistorted and ordered variety of the well-known Fe 2 Pstructure type [3] andits ternary derivative ZrNiAl [4,5]. Aklassengleiche symmetry reduction of index 2(k 2 )from space group P 6 2 m (ZrNiAl) to P 6 2 c (HfPdGa) is accompanied by ad oubling of the lattice parameter c which is causedbyaslight shift of the Hfatoms within the (001) …”

“…Alternatively, HfPdGacan be described as avariant of the Mg 2 Gatype [6] with an ordering of hafnium and gallium atoms on the magnesium positions( 6 h and 6 g ,respectively), while palladium atoms occupy the gallium sites (2f and 4 b ). The number of phases reported with aHfRhSntype crystal structure is relatively small:Z rIrSn, HfCoSn [ 2], ZrRhSn, ZrPtGa [5], ScPdSn, ScPtSn [7]. Palladium and gallium atoms in the crystal structure of HfPdGa build a3Dframework (figure, top) which is exclusively linked by heteronuclearb onds.…”