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Making a Superconductor: Preparation of YBa₂Cu₃O₇

Step 1: Weigh out stoichiometric amounts Step 2: Mix the powders Step 3: Place in a crucible Step 4: Heat in a box furnace Step 5: Cool and grind Step 6: Press into pellets Step 7: Clean the pellet press Step 8: Anneal the sample in Oxygen gas, O2 Step 9: Remove samples and place in a desiccators Testing for Superconductivity

Step 1: Weigh out stoichiometric amounts

Weigh out stoichiometric amounts of the following

Step 2: Mix the powders

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 in a crucible

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

Heat in a box furnace to 930oC and hold for 12 hours.
{*** Keep furnace door closed ***}

Step 5: Cool and grind

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.

Step 6: Press into pellets

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.

Step 7: Clean the pellet press

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: Anneal the sample in Oxygen gas, O₂

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.

Step 9: Remove samples and place in a desiccators

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 for Superconductivity

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 ***}

Making a Superconductor: Preparing YBa₂Cu₃O₇ by Christopher Todd Jones
The procedure described here was personally tested to make hundreds of YBa₂Cu₃O₇ superconductor pellets for my doctoral work at the University of Texas at Austin under the direction of Dr. John McDevitt. This procedure was also adopted for use in UT's general chemistry laboratory.