YbAgGa 2: Synthesis, crystal structure and magnetic behaviour

Abstract

A novel intermetallic compound with two crystallographic modifications, α- and β-YbAgGa 2, was prepared by argon high frequency melting from ingots of the elements in tantalum crucibles with homogenization heat treatments at 600 °C (β-YbAgGa 2) and 400 °C (α-YbAgGa 2). The crystal structure of β-YbAgGa 2 has been refined from powder diffraction data obtained using a Ge(111) primary monochromator and a linear position-sensitive detector. The sample was measured in transmission mode with Cu Kα 1 radiation in the range 10° < 2θ < 130°, Δθ = 0.02°: a = 6.9653(3) A ̊ , b = 4.3362(2) A ̊ , c = 10.3386(4) A ̊ , V = 311.85(4) A ̊ 3 . Full profile refinement led to the residual values R(I) = 0.061 and R(P) = 0.081 (for 303 reflections), space group Pnma, oP16; 4 Yb in 4(c) x 1 4 z, x = 0.2241(2), z = 0.82774(9) , 4 Gal = 0.926(6)Ga + 0.074(6)Ag in 4(c), x = 0.2950(3), z = 0.5369(2), 4 Ga2 in 4(c), x = 0.0751(3), z = 0.1497(2), 4 Ag = 0.951(6)Ag + 0.049(6) Ga in 4(c), x = 0.4595(2), z = 0.0983(1). Coordination numbers are 16 for Yb, 10 for Ga and 12 for Ag. Shortest interatomic distances were revealed for the following: YbGa, 3.014 Å; YbAg, 3.183 Å; YbYb, 3.832 Å; GaGa, 2.622 Å; GaAg, 2.720 Å; AgAg, 3.024 Å. The structure of β-YbAgGa 2 is a distorted variant of the ScRhSi 2 type. Magnetic susceptibility measurements (4.8–900 K) revealed a rather low effective paramagnetic moment for β-YbAgGa 2 (0.5 μ B ( Yb atom) −1, Θ p = 6.5 K ) whereas a tripositive ground state is inferred for α-YbAgGa 2 (about 4.5 μ B (Yb atom) −1, Θ p = −71 K ).