Single-crystal growth of the decagonal Al–Ni–Co quasicrystal

doi:10.1016/S0022-0248(98)00164-X

Journal of Crystal Growth

Volume 191, Issue 3, 15 July 1998, Pages 545-552

https://doi.org/10.1016/S0022-0248(98)00164-X Get rights and content

Abstract

Single-crystal growth of the decagonal Al–Ni–Co quasicrystal has been performed using the floating zone method. Composition of starting polycrystalline rods was selected as Al₇₂Ni₁₂Co₁₆. A large single-quasicrystal of approximately 1 cc was obtained at the growth speed of 0.5 mm/h. High quality of the grown single-quasicrystal was confirmed by the X-ray Laue back-reflection and neutron diffraction methods.

Introduction

Nature of phonon modes and electron wave functions in quasicrystals has been a fundamental issue. For reviews see Refs. 1, 2, 3. To understand them experimentally, it is necessary to measure phonon spectra, electrical resistivity, electron photoemission spectra, and so on. For such experiments, a macroscopic-sized single-quasicrystal of high quality is essential. To date, the Al–Pd–Mn icosahedral quasicrystal is the only one system that can be obtained in centimeter-sized single-grains, and thus, has been intensively studied 4, 5. Unfortunately, for Al–Pd–Mn there is no periodic crystalline-phase with the same composition, so that one cannot compare results with those of the periodic phase. Hence, characteristics inherent to the quasiperiodicity are somewhat obscure.

Unlike icosahedral quasicrystals, decagonal quasicrystals posses both quasiperiodic and periodic directions in one crystal 1, 2, 3. For this structural feature, one can simultaneously compare the physical properties for both the directions. Thus, it is obviously advantageous to perform experiments on the decagonal quasicrystals. Among decagonal quasicrystals ever found, the Al–Ni–Co system is considered to form a single-grain most easily [6]. However, a large single-crystal of good quality has not been obtained even for this system. Thus, experiments on the physical properties have been restricted to polycrystals or single-grains of insufficient volume and quality.

So far, Al–Ni–Co quasicrystals were mainly grown by the slow-cooling method 7, 8, 9. As is well known, this method is not suitable for single-crystal growth because one cannot control spontaneous nucleations during solidification. In comparison, the floating-zone (FZ) method has an advantage in controlling nucleation and growth at the solid–liquid interface. In this study, we applied the FZ method to the single-crystal growth of the Al–Ni–Co quasicrystal. As a result, we successfully obtained a large single-grain of about 1 cc. High quality of the grown quasicrystal was confirmed by the X-ray Laue back-reflection and neutron diffraction methods.

Section snippets

Preparation of feed rods

Button ingots of the Al–Ni–Co alloy were made by arc-melting the constituent elements under an Ar gas atmosphere. Polycrystalline feed-rods were made from the powdered buttons by either arc-melting under an Ar gas atmosphere, or electron-beam (EB) melting under a 10⁻⁵ Torr vacuum. In the former case, nominal composition was chosen as Al₇₂Ni₁₂Co₁₆, and purities of the elements were 99.9% for all, whereas nominal composition of Al₇₃Ni_11.5Co_15.5 was selected in the latter case to compensate an

Solidification of the decagonal Al–Ni–Co quasicrystal

Quasicrystals were long believed to be universally incongruent compounds [11]. The decagonal Al–Ni–Co quasicrystal was also thought to fall into this category, formed by a peritectic reaction [12]. However, Fujiwara, Tsai and Inoue recently reported that Al₇₂Ni₁₂Co₁₆ becomes single decagonal-phase just below melting-temperature, indicating a congruent solidification 13, 14. In order to confirm this result, we examined the solidification process preliminarily by the FZ method. Trial FZ melting

Summary

We have employed the FZ method to grow a single-quasicrystal of the Al–Ni–Co decagonal phase. The preliminary study on the solidification process suggests that the decagonal phase is congruent at the composition of Al₇₂Co₁₂Ni₁₆. A large single-quasicrystal was obtained at the growth rate of 0.5 mm/h. The resulting single-quasicrystal is about 1 cc in volume and of high quality, as confirmed by the X-ray Laue back-reflection and neutron diffraction methods.

Acknowledgements

We thank Mr. Sasaki for EB melting and Mr. Y. Murakami for the WDS measurements. Valuable suggestions from Drs. H. Takeya, K. Shibata and H. Takakura are highly appreciated. This work is partly supported by CREST, Japan Science and Technology Corporation.

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Single-crystal growth of the decagonal Al–Ni–Co quasicrystal

Abstract

Introduction

Section snippets

Preparation of feed rods

Solidification of the decagonal Al–Ni–Co quasicrystal

Summary

Acknowledgements

J. Non-Cryst. Solids

J. Crystal Growth

Acta Met.

Rep. Prog. Phys.

Rev. Mod. Phys.

Mater. Trans. JIM

Phil. Mag. Lett.