1. Synthesis of the heptagonal approximant γ-Gallium Master Project
Michele Zahner
Laboratory for Crystallography ETHZ

2. Quasicrystals and Approximants
Periodic
Quasiperiodic 1 2 3 4 6 5 7 8 10 12
7-fold rotational symmetry: not known, but approximants exist.
Approximant: γ-Gallium

3. Motivation
γ-Gallium: heptagonal approximant made of just one element! Interesting candidate for the synthesis of 7-fold quasicrystals.
Goals:
Synthesis of γ-Gallium
Synthesis protocol for µm-sized Gallium particles
Single-crystal experiment

4. Gallium
Low melting point Polymorphism Vsolid > Vmelt (like H2O)

5. γ-Gallium metastable Orthorhombic oC40 a = 10.593 Å b = 13.523 Å
Tm = °C
z = ¾
z = 0, ½, 1
Bosio, L., A. Rimsky, et al. (1972). Acta Cryst. B 28:

6. Synthesis
Small droplets: less impurities + size effect => easier supercooling
Mix Ga drop, ethanol and emulsifier (SDS)
SDS: Sodium dodecyl sulfate
Heat to 50 °C Shaking by hand Sonication
3. Decantation of solvent, fill up with pure EtOH

7. Single particle diffraction
Typical size: 30 µm
Heating: lamp
Cooling: cryojet
Quenching in situ
Reversible

8. Single particle diffraction
Oxford Diffraction Xcalibur
4-circle diffractometer
CryoJet: N2-Gas cooling unit for in situ experiments
For this work: T = 164K (-110 °C)

9. Results (164 K) orthorombic; a = 10.568 Å b = 13.560 Å c = 5.116 Å
Section hk0
Section 0kl
Section h0l

10. Intergrowth – reciprocal space
Section hk0
Crystallite 1: 0°
Crystallite 2 ~77.1° around c*

11. Intergrowth – real space0°
1 ⋅ 25.7°
2 ⋅ 25.7° = 51.4°
3 ⋅ 25.7° = 77.1°
1/14 ⋅ 2π = 25.7° Best match at 3/14 ⋅ 2π

12. Satellite reflections
h,l sections
Not attributed to additional crystallites or phases
Satellites?
Main reflections
Satellites
Section h1l

13. Reconstruction Integration of dataset with main reflections only
Structure solution by charge-flipping (Superflip)
ED map of CF result with super- imposed γ-Gallium structure
ED-section at z = ¾
Palatinus, L. et al. (2007). Journal of Applied Cryst. 40:
Oszlanyi, G. et al. (2004). Acta Cryst. A 60:

14. Summary µm- to sub-µm-sized Gallium particles were synthesized
A Suitable setup for the synthesis of γ-Gallium was developed (principal task)
γ-phase was obtained reliably at 164 K
Single crystal data were collected and processed
Literature was confirmed but additional features were observed (satellites may indicate modulation)
Outlook: Extending the work to binary alloys in order to find new approximants and quasicrystals