Physical properties of the quasicrystal YbCd_5.7and its approximant YbCd₆

Abstract

We have measured the magnetization, low-temperature heat capacity and electrical resistivity of the binary quasicrystal YbCd 5.7 and its crystalline approximant, cubic YbCd 6 . Magnetization data reveal that Yb ions are divalent in both compounds. The coefficient of the linear term in the heat capacity, γ , is 51 and 7.5 mJ mol −1 K −2 in YbCd 6 and YbCd 5.7 , respectively. The heat capacity data thus reveal a significant reduction in the electronic density of states in the quasicrystalline phase. However, the Debye temperatures of the two compounds are comparable; 144 and 138 K, respectively. The electrical resistivity of YbCd 6 shows typical metallic behaviour while the resistivity of YbCd 5.7 , larger than that of YbCd 6 , is characterized by a negative temperature coefficient below 300 K with a peak around 50 K.

Crystal Structure and Magnetic Properties of the Compounds Yb(Zn,Al)~6 and YbZn~6

“…The transition is interpreted as a low-temperature ordering of the tetrahedral Cd 4 unit inside the icosahedral cluster, described in terms of the B2 structure (changing the space group to Pn3) and the B32 structure (changing the space group to Fd3m upon doubling the unit cell parameter) [25]. A signature of the transition at 110 K in YbCd 6 is also clearly reflected in the resistivity and heat capacity data [25,26]. In Fig.…”

“…The resistivity of YbZn 6 and YbZn 5.44 Al 0.30 at 300 K is 286 and 123 µΩ cm, respectively, varies smoothly with temperature for both compounds, and apparently does not show any anomaly around 60 K, where a peak in the magnetization is observed as described above. It may be recalled here that in the related compound YbCd 6 , in which the Yb atoms are divalent, a disorderto-order transition takes place at 110 K, evidenced clearly by a change of the electron diffraction pattern across the transition [25,26]. The transition is interpreted as a low-temperature ordering of the tetrahedral Cd 4 unit inside the icosahedral cluster, described in terms of the B2 structure (changing the space group to Pn3) and the B32 structure (changing the space group to Fd3m upon doubling the unit cell parameter) [25].…”

Characteristic Electronic State in Quasicrystal Approximants RCd6(R: Rare Earth)

“…The structural transition is found to occur at 164 K in YCd 6 , and 110 K in YbCd 6 [2][3][4], for example, but not to occur in RCd 6 (R = Ho, Er, Tm, and Lu) [5]. It is clarified that the structural transition is not of first-order, but of second-order, revealing the dynamical nature.…”

“…RCd 6 (R: rare earth) compounds are known as approximants to the icosahedral quasicrystals of YbCd 5.7 [1][2][3][4]. It is surprising that this simple binary compound of YbCd 5.7 is the quasicrystal, which has a long-range orientational order but lacks a periodic translational order.…”

Intermediate-Valence Quasicrystals of Yb-Based Alloys Under Pressure

“…As for Yb-based quasicrystals, γ of i-CdYb, which has been reported as 2.87 mJ/mol K 2 or 7.5 mJ/mol K 2 , 12,13) should increase upon compression. The observed valence regions of i-CdYb and i-CdMgYb are less than 2.4.…”