Intermetallic Cerium Compounds with Ordered U₃Si₂ Type Structure

Abstract

Intermetallic Cerium Compounds, Crystal StructureNew intermetallic cerium compounds Ce2 7iMg (T = Ni, Cu, Pd), CqiTjCd (T -Pd, Pt, Au), and CtiTzPb (T = Pt, Au) were prepared by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. Most C e :^^ (X = Mg, Cd, Pb) compounds are stable after annealing at about 1000 K, while Ce:Pd2Mg is obtained as single phase only after melting and quenching. A thermal treatment at about 1000 K leads to decomposition in CePdMg and CePd. The eight compounds were investigated by X-ray diffraction both as powders and single crystals, and most structures were refined from single crystal data. They adopt an ordered l^Si? type structure with space group PA/mbm: a = 759.6( 1), c = 376.71 (9) pm, wR2 = 0.0562, 294 F values, 12 parameters for Ce2Ni2Mg, a = 787.41(9), c = 387.23 (7) pm, wR2 = 0.0438, 222 F2 values, 12 parameters for Ce2Cu2Mg, a = 777.14(8), c = 400.03 (7) pm, wR2 = 0.0276, 221 F2 values, 13 parameters for Ce2Pd2.03Mg0.97, a = 777.90(6), c = 393.28(6) pm, wR2 = 0.0360,317 F2 values, 12 parameters for Ce2Pd2Cd, and a = 779.90 (7), c = 389.97(7) pm, wR2 = 0.0453, 315 F2 values, 12 parameters for Ce2Pt2Cd. Refinement of the occupancy parameters revealed full occupancy for most sites. A mixed palladium/magnesium (97 % Mg / 3 % Pd) occupancy was observed only for the 2a site of Ce2Pd2.03Mg0.97, indicating a small homogeneity range for this compound. Ce2Au2Cd (a = 804.93 (7), c -393.36(6) pm) and the plumbides Ce2Pt2Pb {a = 794.63 (7), c = 381.50(6) pm) and Ce2Au2Pb (a -810.70 (7), c = 394.85(7) pm) were characterized through their Guinier powder data. The structures of the Ct2 FX compounds can be interpreted as an intergrowth of distorted AIB2 and CsCl related slabs of compositions CzTi and CeX. The course of the lattice parameters and chemical bonding within the series of C^TjX compounds are briefly discussed.

Antiferromagnetic ordering in the heavy-fermion systemCe2Au2Cd

“…1 agree with in experimental error with the values of a = 809.2(1) pm, c = 400.27(9) pm for La 2 Au 2 Cd and a = 804.93(7) pm, c = 393.36(6) pm for Ce 2 Au 2 Cd previously reported in Refs. [8,12].…”

“…The increase in palladium content leads to a decrease of the magnetic ordering temperature. 5,6 The cerium atoms in Ce 2 Pt 2 Sn are trivalent and this stannide shows two magnetic transitions at 2.5 and 6.5 K. 7 In parallel to the stannides, also some plumbides Ce 2 T 2 Pb (T = Rh, Pd, Pt, Au) 5,[8][9][10] have been synthesized. Ce 2 Pd 2 Pb 5 is a 6.2 K antiferromagnet and Ce 2 Rh 2 Pb 10 behaves like a normal metal.…”

“…Recently, the first cadmium containing compounds have been reported, 8,[11][12][13][14] where the X site is completely occupied by cadmium. This substitution leaves opportunities for varying the properties, since cadmium reduces the valence electron count per formula unit by two with respect to the stannides and plumbides.…”

Ca2Pd2Cd with W2B2Co-type Structure

“…1. Again the palladium and cadmium atoms build up a two-dimensional [Pd 2 Cd] network, however, the latter solely consists of distorted Pd 3 Cd 2 pentagons with much longer Pd-Cd (306 pm) and Pd-Pd (282 pm) distances [28]. These layers are stacked in AA sequence, and they are separated and charge-balanced by the cerium atoms.…”

Synthesis and Crystal Structures of REAgMg (RE=La, Ce, Nd, Eu, Gd, Tb, Ho, Tm, and Yb)

“…Besides the series RE ¹ Mg (¹"Ni and Cu) (4,8,14), RE Au Cd (RE"La, Ce, Pr, Nd, Sm) (7,12) and Ce Ni Cd (10) with tetragonal Mo FeB -type structure (16) and also the equiatomic compounds RE¹Mg (¹"Pd, Ag, Au) (3,4,9) and RE¹Cd (¹"Cu, Pd, Au) (2,6,12) have recently been studied. The latter crystallize with the orthorhombic TiNiSi-type structure (17) when the rare earth element is divalent and with the hexagonal ZrNiAl-type structure (18}20) in the case of trivalent rare earth metals.…”