Synthesis, Crystal Structure, Transport, and Magnetic Properties of Novel Ternary Copper Phosphides, A₂Cu₆P₅ (A = Sr, Eu) and EuCu₄P₃

Abstract

Three new ternary copper phosphides, Sr(2)Cu(6)P(5), Eu(2)Cu(6)P(5), and EuCu(4)P(3), have been synthesized from the elements in evacuated silica capsules. Eu(2)Cu(6)P(5) and Sr(2)Cu(6)P(5) adopt the Ca(2)Cu(6)P(5)-type structure, while EuCu(4)P(3) is isostructural to BaMg(4)Si(3) and still remains the only representative of this structure type among the ternary Cu pnictides. All three materials show metallic conductivity in the temperature range 2 K ≤ T ≤ 290 K, with no indication for superconductivity. For Eu(2)Cu(6)P(5) and EuCu(4)P(3), long-range magnetic order was observed, governed by 4f local moments on the Eu atoms with predominant ferromagnetic interactions. While Eu(2)Cu(6)P(5) shows a single ferromagnetic transition at T(C) = 34 K, the magnetic behavior of EuCu(4)P(3) is more complex, giving rise to three consecutive magnetic phase transitions at 70, 43, and 18 K.

Structural Series in the Ternary A–Mn–As System (A = Alkali Metal): Double-Layer-Type CsMn4As3 and RbMn4As3 and Tunnel-Type KMn4As3

“…Figure a shows the KCu 4 S 3 -type structure in which Cs143 and Rb143 crystallize. In contrast to the prevalent ThCr 2 Si 2 -type structure, the double-layer structure has been mostly reported in late TM- or Mg-containing compounds, for example, KCu 4 S 3 , RbZn 4 As 3 , CePdGa 6 , EuCu 4 P 3 , and BaMg 4 Si 3 . ,− Cs143 and Rb143 are thus the first examples of double-layer compounds containing a middle TM atom. The characteristic double layer is composed of two PbO-type MnAs layers connected by eight-coordinated As atoms (As2), and another type of As atom (As1) occupies the fringe of the double layer.…”

“…32,33 It is also informative to compare the metallic conductivities of single-layer-type LiCu 2 P 2 and EuCu 2 P 2 with those of double-layer-type KCu 4 S 3 and EuCu 4 P. The conductivities at 300 K are 0.05 and 0.14 mΩ cm for LiCu 2 P 2 and EuCu 2 P 2 and 0.25 and 0.30 mΩ cm for KCu 4 S 3 and EuCu 4 P 3 . 17,19,34,35 The similar metallic conductivities of the single-and double-layer compounds indicate that the doublelayer structure does not significantly affect the transport properties of the insulator and metal. Figure 5a shows the temperature dependence of the magnetic susceptibility of Rb143 under a magnetic field of 30 000 Oe.…”

Experimental and Theoretical Studies on the Crystal Structure of Ternary Copper Arsenides A2Cu3As3 (A = Sr, Eu)

“…Owing to their complex crystal structures, the magnetic properties of these phases are also interesting. Ferromagnetism was demonstrated for the europium copper arsenide Eu 7 Cu 44 As 23 with a ferromagnetic ordering temperature of 17.5 K. Complex consecutive magnetic transitions were reported for EuCu 4 P 3 below 52 K . EuCuAs exhibited an antiferromagnetic transition with a Néel temperature of 14 K, and a metamagnetic (MM) transition was observed when the magnetic field was parallel to the ab plane …”

“…The A–Cu–Pn ternary system (A = alkaline‐earth or rare‐earth metal, Pn = P, As) constitutes a huge family, and the relevant structural units are very flexible . In addition to the compounds based on simple CuPn 4 tetrahedra such as CaCu 2 As 2 and BaCu 2 As 2 , other copper‐rich or clathrate‐like analogues with very complex anions such as Ba 8 Cu 18– x As 10 and Eu 7 Cu 44 As 23 are also commonly seen, and the electrons in these compounds cannot be counted by the octet rule.…”

Effect of Transition Metal Substitution on the Structure and Properties of a Clathrate-Like Compound Eu7Cu44As23

“…The vast majority of these compounds contain divalent europium, with the 4 f 7 ground state configuration giving rise to strong paramagnetic response and, eventually, magnetic ordering. It is worth noting that the pseudo-layered compounds typically feature antiferromagnetic (AFM) ordering [7], whereas ferromagnetic (FM) ordering is rare—Eu 2 Cu 6 P 5 and EuCu 4 P 3 being the only examples [9]. On the contrary, compounds with 3D structures frequently display FM ordering, as in the clathrate compound Eu x Ba 8− x Cu 16 P 30 , exhibiting a superstructure of the type-I clathrate [10], and in the recently discovered clathrate-like compound Eu 7 Cu 44 As 23 [11].…”