Preparing YBa2Cu3O7
Step 1: Weigh out stoichiometric amounts of the following:
| Y2O3 |
Yttrium Oxide |
1/2 mole |
| BaCo3 |
Barium Carbonate |
2 moles |
| CuO |
Copper Oxide |
3 moles |
Precursors Used to Make YBa2Cu3O7
Step 2: Mix the powders together until the mixture is a uniform
grey color. One way to simplfy this is to add just enough acetone to get
the powders wet. Then, mix until you have a dry powder.
Step 3: Place the mixture into an alumina crucible. Do
not use a porcelain crucible as this will contaminate the superconductor.
Step 4: Heat in a box furnace to 930oC and hold for
12 hours.
{*** Keep furnace door closed ***}
Box Furnace at 930oC
Crucible of Superconductor
Step 5: Upon cooling to room temperature the sample will be
a hard black "chunk". Grind the sample into a fine powder. (As a "rule
of thumb", grind until you can not feel any hard bits of superconductor.
Then grind for another 5 minutes). Repeat Step 4-5 two more times.
Mortar and Pestle Beside a Pellet Press
Pressing Superconductor Pellets
Step 6: Using a clean pellet press (or a KBr press), press the
powder into small pellets. For a 0.5 inch diameter pellet press use 0.5
grams. Transfer the pellet to an alumina combustion boat. Again. do not
use porcelain. The pellet is quite fragile at this point so transfer the
pellet carefully. It is not unusual for the pellet to break at this stage.
If it does, regrind and try again.
Small and Large Superconductor Pellets
Step 7: Clean that pellet press! It is important that
the press is cleaned between pressing each pellet. You can easily ruin
it by not properly cleaning it. Use acetone or ethanol to clean it. Avoid
water if possible.
Step 8: This step is to adjust the stoichiometry of the oxygen
in the superconductor to its optimal level. Place the combustion boat into
a tube furnace. Turn on a flow of oxygen through the tube furnace. You
can use a mineral oil bubbler to set your rate at about 1-2 bubbles per
second. Heat the sample to 450oC . Hold for 8 hours. Slow cool
the samples to room temperature. If you can control the cooling rate, have
it cool at 30oC per hour.
Tube furnace
Step 9: Remove the samples from the tube furnace and place them
in a dessicator. The humidity in the atmosphere will cause the compound
to degrade.
Testing the Superconductor
You can test the superconductor's properties if you have a strong rare
earth magnet and some liquid nitrogen. Place the pellet in a "shortened"
syrofoam cup or a pyrex crystallation dish. Add a small amout of liquid
nitrogen. As soon as the pellet is cool, add the magnet with a pair of
plastic tweezers. Since a superconductor is a perfect diamagnet, it will
repel the magnet. If moving the superconductor close to the magnet (but
not touching it) causes it to move, then you have a superconductor. If
your pellet is large enough and the magnet is strong enough. You may even
be able to get the magnet to leviate above the superconductor.
{*** Always use caution when handling liqiud nitrogen, it's low temperature
may cause "frost-bite" in only seconds ***}
Magnet Levitating Above Large YBa2Cu3O7
Superconductor
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