GROWTH OF SINGLE CRYSTAL RUBY Charis Cochran 1,2, Drew Rebar 2, Jennifer Neu2,3, Theo Siegrist 2,3 Trevecca Nazarene University1, National High Magnetic Feild Laboratory2, Florida State University3

The use of the image furnace to grow ruby yielded large single crystalline sections of ruby that can be observed easily by eye. In the future growth parameters, hanging wire, and the process for making polycrystalline feed rods will be modified to grow larger single crystals that can be used for a variety of applications.

Condensed Matter Science

I would like to give a special thanks to the MagLab Internship program for allowing me to participate in this research and to Dr. Theo Siegrist and Drew Rebar for the guidance throughout the summer.

Single crystal Ruby, a form of Alumina (!-Al2O3) with Chromium used as a dopant, was grown using the Optical Floating Zone technique in the Image Furnace. Two polycrystalline rods with .3-1.5 wt% Chromium, were used as preforms for the Image Furnace growth. The grown crystals had very large single crystalline, optically active sections .

ABSTRACT

Feed Rod

Seed Rod

Polycrystalline Rod

Seed Crystal (or Polycrystalline Rod)

Single Crystal

Lamp Lamp

Mirror Mirror

Hot Zone (Molten Material)

Seed Crystal (or Polycrystalline Rod)

Platinum/Tantalum Wire

single crystalline, optically active sections .

PROPERTIES OF RUBY

PREPARATION

RESULTS ACKNOWLEDGEMENTS

IMAGE FURNACE GROWTH

Figure 2 Phase Diagram for Ruby1

Figure 1 Crystal Structure for Alumina Family (Aluminum-Blue, Oxygen-Red)

Drawn Using VESTA

Playdough Method

Playdough Press Method

Press Method

Successful Growth Using Playdough Method Rod

18 mm

Preliminary Growths Using Pressed Fragments

Green Contaminant on Feed Rod

Figure 4 Image Furnace

Image Furnace Control Panel Images from Camera Inside Furnace

Molten Zone

Two polycrystalline rods are used in the image furnace technique, which are made of pressed powder. Alumina and Chromium Oxide were mixed to the specific percent Chromium content, forming a green powder that was sintered at 1100C to react the Chromium Oxide with the Alumina and make a pinkish polycrystalline powder. The powder was pressed into rod shape in a hydrostatic press to 40kN. The rods were too fragile, so a playdough method was attempted where the material was mixed with ethanol to form a clay that was shaped into a rod by hand. This rough rod was sintered at 1260C overnight. These rods were rough as the rod flaked apart since it was not very dense. The best method was a combination where the playdough rods were re-crushed and pressed and sintered, giving rigid rods suitable for growth (right).

The crystal structure is identical to that of Sapphire and Corundum (Figure 1), differing only by the Chromium dopant used to give Ruby it’s red color. The Chromium gives the naturally clear Sapphire its ruby red color. When Chromium replaces the aluminum centers it loses electrons to maintain the charge balance and these localized electrons in their ground state can be excited by white light which causes the ruby to appear red. The chemical formula for Ruby is CrxAl2-xO3, where x is the percent weight of chromium in the Ruby which corresponds to how dark the red will be 2,3. When heated above 1000C the Chromium is incorporated into the structure of alumina, as 3d3 ion centers (Figure 3). Ruby is a rhombohedral crystal system, its space group is R3c. Ruby possesses great optical properties and is a good lasing medium. Ruby is also highly insulating, and is a good dielectric material and substrate material for GaN3. Ruby is also one of the hardest substances having a Mohs scale hardness of 9, falling just below diamond at 10.

1.! Theodore M. Besman, and Nagraj S. Kulkarni, and K.E. Spear. “Thermochemical analysis and modeling of Al2O3-Cr2O3,Cr2O3-SiO2, and Al2O3-Cr2O3-SiO2 systems relevant to refractories.” Journal of American Ceramic Society (Feb. 2006). Web. June 2017.

2.! "Ruby." Chemical Structure. N.p., 06 Apr. 2016. Web. 23 July 2017 3.! Xiujun Fan, and Yue Wang, Hong Xu, and Yijian Jiang. "Floating zone growth and

characterization of ruby single crystals.” Cryst. Res. Technol. 46, No. 3, 221 – 226 (2011).Web. June 2017.

Crystal Vector Art Designed by Freepick http://www.freepik.com/free-vector/colorful-gemstones_968024.htm

The Image Furnace is a system of elliptical mirrors and energized filaments (High Wattage Lamps). The mirrors focus the energy into what is called the hot zone. Below the hot zone a polycrystalline rod (sometimes with a seed crystal in a desired orientation or a flux to help growth) is attached to the seed rod. A polycrystalline rod is attached to the top feed rod with wire that has a high melting point. As the two rods come into the hot zone the ends of the rods melt and are then brought together so that they are connected by a molten zone. The rods are then pulled down through the hot zone, propagating the molten area through the feed rod. As each section of the rod moves out of the hot zone it recrystallizes into a single crystal.

The Ruby on the right was grown over the course of 9 hours. When analyzed in crossed Polarizers it is clear that the rod is not completely single crystalline, but there are very large crystallites in the same orientation. This growth was done using the playdough method polycrystalline rod. Some preliminary growths using fragmented pieces were done yielding small drops of ruby.

With the rod making process resolved, and successful single crystal growths, the research has turned to improving the quality of the crystal. One of the first problems was the suspending wire becoming brittle and causing the feed rod to jerk around during the growth, and even break, causing the feed rod to fall. This problem was due to the fact that the tantalum wire used, while withstanding high temperatures without melting, oxidizes in the 2200C air environment. There was also a green film on the outside of the feed rod of unknown composition, but thought to be due to the wire oxidizing.

Figure 3 Addition of Chromium to Alumina2

Large Single Crystal Large Single Crystal

ion centers (Figure 3). Ruby is a rhombohedral crystal system, its space group is R3c.

Powder X-ray diffraction on scrapings of this film revealed that there are in fact discrepancies in the peaks expected and observed. Further analysis of the sample will be conducted to determine if there are other inclusions besides Chromium in the Alumina, and to find the composition of the green substance. Single crystal X-ray diffraction analysis of the grown crystal will also be conducted to confirm structure and determine the growth orienttion. The large grown crystal was observed with cross polarizers to reveal the optically active larger portions of single crystal ruby.

Figure 4 Powder diffraction of green film compared to expected Ruby diffraction pattern

IMAGE FURNACE

ANALYSIS AND CONTINUED RESEARCH

I would also like to thank Shengzhi Zhang for instruction on how to preform Image Furnace Growths, and Jennifer Neu for instruction on X-Ray diffraction. This research was sponsored by DMR-1157490.

CONCLUSION/FUTURE DIRECTIONS