From SSSPH@jazz.ucc.uno.edu Mon Dec 13 01:37 MET 1993 Return-Path: Received: from jazz.ucc.uno.edu by bellatrix.tdb.uu.se (5.0/SMI-SVR4) id AA24046; Mon, 13 Dec 93 01:37:05 +0100 Received: from jazz.ucc.uno.edu by jazz.ucc.uno.edu (PMDF #2820 ) id <01H6EHHYABPS8X9OQ8@jazz.ucc.uno.edu>; Sun, 12 Dec 1993 18:35:05 CST Date: 12 Dec 1993 18:35:05 -0600 (CST) From: SSSPH@jazz.ucc.uno.edu Subject: Re: High Tc superconductor receipt To: t89djo@tdb.uu.se Message-Id: <01H6EHHYABPU8X9OQ8@jazz.ucc.uno.edu> X-Vms-To: IN%"t89djo@tdb.uu.se" Mime-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: TEXT/PLAIN; CHARSET=US-ASCII Content-Length: 6239 Status: RO Hi David, Here is the recipe for H-Tc superconductor, it is true that you will need to blow oxygen at the sample at high temprature, but if you have a furnace capable of about 1000 degree C and a simple quartz or vicor tube, it is quite easy to make it. You need to have the furnace in any event. I am sending you a small report that I wrote, if you have any questions please don't hessitate to ask. By the way what is your position at Uppasala? Sincerely, Siddharth Saxena. UNO Physics. ================================================================================ PREPARATION OF HIGH TC SUPERCONDUCTOR Siddharth S. Saxena Department of Physics, University of New Orleans 4 May 1992 There is a class of metals and compounds whose resistivity goes to zero below a certain temperature Tc, called the critical temperature. These materials are known as superconductors. Here we will discuss the preparation of a High Tc superconductor. This particular type of superconductor is formulated as MBa2Cu3Ox, where M = Rare Earth. INTRODUCTION : As temperature is lowered considerably, some metals undergo a change of phase into what is called a super conducting state. A superconductor has many unusual thermal, electrical, magnetic. and optical properties The most amazing characteristic of a super conductor is its electrical resistance. Every metallic conductor opposes the passage of electrical charge through it. This opposition arises because of the moving charges collide with vibrating atoms in crystal structure of solids and other particles of the conductor. In doing so, the moving charges give up energy. In perfect single crystal-no dislocations, no impurities, and no lattice vacancies-at low temperatures, electrical resistance will be at a minimum. Some super conducting metals and compounds, when cooled to low temperatures, carry currents without diminutions. This is mainly because electrons can slip through crystal lattices at low temperatures with little loss of energy. Superconductivity above the boiling point of liquid nitrogen, which is 77K, was first noticed in the compound YBa2Cu3O7. This type of superconductor is known as High Tc super conductor. Now we will go on to describe to how to prepare this super conducting sample. APPARATUS: The apparatus needed to produce a YBa2Cu3Ox sample includes an accurate balance, a set of pastel and mortar, a crucible, and a good thermocouple. Procedure also requires a Quartz or Vicor tube of about two inch diameter and 2.5 feet length. This tube should be sealed at one end with only a point hole in it and the other end should be fitted with a rubber cork so that the cork can be removed to place the crucible in the tube. The cork should have a small hole in it to support a delivery tube for oxygen flow. Also needed is an oven capable of producing temperatures up to 950 c, for the heat treatment of the sample, and a tank of oxygen. MATERIALS: The materials needed to prepare a YB2Cu3Ox superconductor are listed below: COMPOUND FORMULA PURITY Yttrium oxide Y2O3 99.99% Barium Carbonate BaCO3 99.80% Cupric Oxide CuO 99.50% QUANTITY: COMPOUND MOLECULAR WEIGHT Y2O3 1/2 225.81 g BaCO3 2 197.35 g CuO 3 79.546 g Molar Calculation: Actual Masses Used Y1O1.5 1.121 g BaCo3 3.947 g CuO 2.386 g PROCEDURE: The first step in the preparation is the accurate calculation of the molar amounts of the materials to be used. The amounts must be accurately measured to ensure the correct 123 phase of the High Tc superconductor. The purity of the materials is also a factor in final results. After the compounds are measured, they are placed in the mortar and mechanically grounded with the mortar for a period of approximately thirty minutes to acquire a thorough mixing of the constituents an to provide spatial uniformity. Then this finely grounded mixture is placed into a crucible, which in turn, is placed in an oven. The temperature of the oven is maintained at 890 c for about 25 hours and at this temperature the sample is allowed to react in air. Then the oven is cooled down to room temperature at the rate of 5 c per minute and regrounded and placed in the oven again for another round of heating at 890 c for 25 hours. This process is repeated once again. Now the mixture is taken out and grounded once again and then placed in the crucible. Once the mixture is in the crucible, it is slightly pressed to form a pellet. The crucible then is placed into the glass tube. Now the glass tube is placed in the oven and is corked up. At this point a thin delivery tube is fitted into the hole in the cork and the tube is connected to the Oxygen tank via rubber hose. Oven, now is heated up to 950 c and the Oxygen is turned on. The flow of the oxygen is maintained at a low rate. The hole at the end of the tube should small enough to build up a slight pressure in the tube. The apparatus is kept in this condition for 45 hours and then cooled down to 500 c at the rate of 2.5 c per minute. This condition is maintained for 6 hours and then the apparatus is cooled down to the room temperature at the rate of 2.5 c per minute. The YBa2Cu3O7, 123 phase superconductor is now ready. The pellet is now taken out of the crucible, filed into the desired shape, and polished. OBSERVATIONS: Now the pellet is immersed in the liquid Nitrogen. At this time a small magnet is placed on the pellet and it can be observed that the magnet is levitated into the air. PRECAUTIONS: Yttrium Oxide is a hygrophobic compound and its contact with the body and inhalation should avoided. Other chemicals should be treated with care also. Great caution should be taken while handling hot apparatus and electrical equipment.