High pressure synthesis of a new phase of YbAg2: Structure, valence of Yb and properties

Abstract

The new phase of YbAg 2 was obtained using high-pressure and high-temperature reaction. YbAg 2 crystallizes in the MgZn 2 structure (the space group P6 3 /mmc space group, № 194) with a = 5.68153(3) Å and c = 9.31995(7)Å and the unit cell volume V = 260.54(3) Å 3. The XANES analysis showed that the valence state of Yb is +2.8. The low-temperature dependences of the electrical resistivity and magnetic susceptibility can be adequately described by a T 2 term that supports the Fermi-liquid picture. The Kadowaki-Woods relation gives a low value of the degeneracy (N = 2).

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

“…On replacing A by lighter alkaline earth metal elements, the corresponding Laves phases CaAl 2 and MgZn 2 are obtained, both of which are stable at ambient pressure. A low-pressure CeCu 2 -type and a high-pressure C14 polymorph also appear to exist for YbAg 2 [74]. Similarly, a pressure-induced CeCu 2 ?…”

Two-stage pressure-induced Yb valence change in the hexagonal Laves phase YbAg2 : Investigation by time differential perturbed angular γ−γ correlation spectroscopy method and density functional calculations

“…The 111 In activity was produced via the 109 Ag (α, 2n) 111 In reaction through irradiating a silver foil with the 32 MeV α-beam at the Nuclear Physics Institute cyclotron (Moscow State University). The 111 In -111 Cd nuclear probes were introduced into the lattice of YbAg 2 by the high-pressure synthesis: the constituents (Yb and Ag) taken in proper amounts with an overall weight of about 600 mg were melted together with a piece of the irradiated silver foil (1 mg) in a special chamber under pressure of 5 GPa [18]. The X-ray diffraction pattern presented in Fig.…”

“…The X-ray diffraction pattern presented in Fig. 1 confirms the hexagonal Laves phase [18]. As the samples were polycrystalline and paramagnetic at temperatures above 4 K, the perturbation of the angular correlation can be described by the perturbation factor G 22 for the static electric quadrupole interaction (EQI) [25]:…”

“…Changeable ytterbium valence is also observed in novel metastable compounds synthesised under high pressure and temperature conditions [15][16][17][18]. However, despite much experimental effort, the trivalent state of Yb in these intermetallic compounds has not been achieved even at sufficiently high pressures [17,[19][20][21].…”

“…At ambient pressure YbAg 2 has the orthorhombic structure of the CeCu 2 type [23], which is non-magnetic with the divalent state of Yb. Since the divalent state of ytterbium implies conventional behaviour, for our experiments we have chosen the hexagonal phase of YbAg 2 crystallized in the (C14) MgZn 2 structure (at pressure of 5 GPa), where the valence of ytterbium is 2.8 [18]. In the hexagonal phase a silver atom can be easily substituted with the 111 Cd probe and as a result we can create a relatively high density of 111 Cd nuclei required for the TDPAC measurements of hyperfine interactions parameters under high pressure.…”