Physical Properties and Bonding in RE₃TiSb₅ (RE = La, Ce, Pr, Nd, Sm)

Abstract

Electrical transport and magnetic properties have been measured for the family of ternary rare-earth transition-metal antimonides RE 3 TiSb 5 (RE ) La, Ce, Pr, Nd, Sm). Single-crystal X-ray structures have now been determined for all members of this series. All are metallic, with anomalies appearing in the resistivity curves suggestive of electronic transitions. La 3 -TiSb 5 , Ce 3 TiSb 5 , and possibly Nd 3 TiSb 5 undergo transitions to a superconducting state below ∼4 K. Support for the existence of a superconducting phase is also provided by onset of diamagnetism in the magnetization behavior below T C . Extended Hu ¨ckel band structure calculations disclose strongly anisotropic electrical conductivity, reflecting the onedimensional character of covalent bonding within the structure, and reveal the presence of narrow Ti-based bands close to the Fermi level.

Structure and physical properties of ternary uranium transition-metal antimonides U3MSb5 (M=Zr, Hf, Nb)

“…The change in slope is clearly visible in the plots of dρ/dT versus T, shown in the insets. The presence of a transition at slightly lower temperatures is also observed for some members of the isostructural RE 3 MSb 5 (M = Ti, Zr, Hf) series [9]. Because this resistivity behaviour is similar to that seen in many other rare-earth intermetallics where magnetic ordering arises from coupling of f electrons via conduction electrons, magnetic measurements were carried out to probe the nature of these transitions.…”

“…A Zintl-type formulation (U 3+ ) 3 M 4+ (Sb 3− ) 3 (Sb 2− ) 2 may then be proposed, but the true bonding character is likely highly covalent, even more so than in the corresponding RE analogues. In particular, the M-M distances of 3.0-3.1Å within the chains of metalcentred octahedra may be indicative of weak metal-metal bonding, as has been implicated in La 3 TiSb 5 [9], as opposed to a consequence of matrix effects. For U 3 NbSb 5 , where a d 1 configuration for Nb 4+ permits the formation of metal-metal bonds, the formulation is reasonable, but for U 3 ZrSb 5 and U 3 HfSb 5 , a d 0 configuration for Zr 4+ or Hf 4+ seems inconsistent with metal-metal bonding.…”

“…A series of ternary uranium antimonides U 3 MSb 5 , where M is an early transition metal (Ti, V, Cr, Mn), was first identified by Brylak and Jeitschko [6], and subsequently extended by us to the rare-earth analogues RE 3 MSb 5 (RE = La, Ce, Pr, Nd, Sm; M = Ti, Zr, Hf, Nb) [7,8]. A band structure calculation for La 3 TiSb 5 suggested that it and other RE 3 MSb 5 compounds may be subject to an electronic instability, which may account for prominent transitions observed in the electrical resistivity curves in the RE 3 TiSb 5 series [9]. Unlike RE elements, where the 4f electrons are highly localized, there is a greater tendency * Corresponding author.…”

Electride and superconductivity behaviors in Mn5Si3-type intermetallics

“…This means the octahedral chains along the c-axis become increasingly distorted when Nb-O bonds are formed. As in a similar interstitial filled Sb 5 RE 3 Ti (RE: rare earth), 41 the position of the Fermi level is quite sensitive to even minor changes that lead to small contractions in the structure. Ir is the most electronegative component among these metal elements and, therefore, the Zintl concept may be applicable by assuming that a full electron transfer takes place.…”

Ternary rare-earth titanium antimonides: Phase equilibria in the RE–Ti–Sb (RE=La, Er) systems and crystal structures of RE2Ti7Sb12 (RE=La, Ce, Pr, Nd) and RETi3(SnxSb1–x)4 (RE=Nd, Sm)

“…Systems containing a late transition metal have been the focus of most previous studies, whereas those containing an early transition metal remain poorly investigated. When M is a group 4, 5, or 6 element, the only compounds known so far are RE 3 MSb 5 (M ¼ Ti, Zr, Hf, Nb) [2][3][4][5], REMSb 3 (M ¼ V, Cr) [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], and REZrSb [23][24][25][26]. In the Sb-rich phases, homoatomic Sb bonding networks are a recurring feature of the structures, in the form of one-dimensional chains in RE 3 MSb 5 or two-dimensional nets in REMSb 3 .…”