Eu Doping in the GdCd Quasicrystal and Its Approximant Crystal GdCd.

The effect of Eu doping in the Tsai quasicrystal (QC) GdCd and its periodic 1/1 approximant crystal (AC) GdCd are investigated. This represents the first synthesis of Eu-containing stable QC samples, where three samples with the final composition GdEuCd at Eu doping concentrations = 0.06, 0.13, and 0.19 are obtained (α ∼ 0.2). They are compared to two 1/1 ACs with compositions GdEuCd ( = 0.12, 0.16). In addition, a new type of 1/1 AC, differing only by the inclusion of extra Cd sites unique to the EuCd 1/1 AC, has been discovered and synthesized for the concentrations GdEuCd ( = 0.25, 0.33, 0.45, 0.69, 0.73, and 0 < δ ≤ 0.085). Due to the preferred cube morphology of its single grains, we refer to them as c-type 1/1 ACs and to the conventional standard ones as s-type. In both QCs and s-type ACs, the Eu content appears to saturate at a concentration of ∼20%. On the other hand, any Gd| Eu ratio is allowed in the c-type ACs, varying continuously between GdCd and EuCd. We describe and contrast the changes in composition, atomic structure, specific heat, and magnetic properties induced by Eu doping in the quasicrystalline phase and the s-type and c-type 1/1 ACs. By comparing our results to the literature data, we propose that the occupancy of the extra Cd sites can be used to predict the stability of Tsai-type quasicrystalline phases.