Tuning icosahedral quasicrystals and their approximants from the Mg₂Zn₁₁ structure

Abstract

Electronic tuning of Sc−Mg−Zn icosahedral quasicrystal (i-QC) and approximant (AC) phases was achieved according to pseudogap predictions from an electronic band structure analysis of Mg₂Zn₁₁. The i-QC and two AC phases were obtained in the Mg_{2- x} Sc _x Zn₁₁ system. The QC compositions are Sc_10.8(6)Mg_3.2(6)Zn_86.0(2) and Sc_14.6(4)Mg_3.3(4)Zn_82.1(2) by EDX for x = 1.0 and 1.5, respectively. X-ray structure determination reveals that the 1/1 AC, Sc₃Mg_0.18(1)Zn_17.73(1), crystallizes in space group Im , with a = 13.863(2) Å. Electronic structure calculations on the 1/1 AC reveal that the Fermi level is located in the centre of the pseudogap, which appears to be greatly enhanced by Zn 4p and Sc 3d orbital mixing.

Acknowledgement

The authors thank M. J. Kramer and Y. Wu for the TEM results. This research was supported by the U.S. National Science Foundation, Solid State Chemistry, via grants DMR-9809850 and -0129785 and was performed in facilities of the Ames Laboratory, U.S. Department of Energy. The Ames Laboratory is operated for DOE by Iowa State University under Contract No. W-7405-Eng-82.