Neue Pnictide im CaAl2Si2-Typ und dessen Existenzgebiet/New Pnictides with the CaAl2Si2 Type Structure and the Stability Range of this Type

Five new compounds were synthesized by heating mixtures of the elements at 600 - 1000 °C and investigated by powder and single crystal X-ray methods. EuMg2P2 (a = 4.280(1), c = 7.164(3) Å), EuMg2As2 (a = 4.393(1), c = 7.321(1) Å),EuMg2Sb2 (a = 4.695(1), c = 7.724(2) Å), YbMg2Sb2 (a = 4.650(1), c = 7.540(2) Å), and SrLiAlSb2 (a = 4.584(3), c = 7.697(9) Å) crystallize with the CaAl2Si2 type structure (P3̄m1; Z = 1). The magnetic susceptibility of EuMg2Sb2 shows Curie-Weiss behavior with an experimental magnetic moment of 7.48(2) μB/Eu atom and a Weiss constant θ = 3.2(1) K. EuMg2Sb2 is ordered antiferromagnetically at 8.2(3) K. Magnetisation measurements at 4.5 K show a linear increase and a saturation for a magnetic moment of 5.9(1) μB/Eu at 5.5 T, indicating an almost parallel spin alignment with increasing field strength. 151Eu Mössbauer spectra at 78 K show an isomer shift of -11.69(5) mm/s, compatible with divalent europium. At 4.2 K we observe full hyperfine field splitting with 23 T. The 121Sb spectrum at 4.2 K shows a transferred hyperfine field of 8(2) T at an isomer shift of -7.9(3) mm/s. From the band structure of EuMg2Sb2 we draw the conclusion, that analogous compounds of trivalent rare-earth metals with CaAl2Si2 type structure should not exist due to electronic reasons.