Synthesis of Superconductor (2020/05/08 revised) Collect: Agate - PowerPoint PPT Presentation

Synthesis of Superconductor (2020/05/08 revised) Collect: • Agate mortar (clean with sponge after use) • Label one zip-lock bag with student ID and name (To collect the synthesized superconductors) Prepare: • Plastic spatula x1 • Mask (self-prepared) 1

Superconductors  Metal conductors Conductivity decreases with increasing temperature  Semiconductors Semiconductor Resistance Conductivity increases with Superconductor increasing temperature  Superconductors Zero resistance at transition Conductor temperature, T c 0 0 T c Temp. (K) 2

Properties of Superconductor Magnet Superconductor (b) The Meissner effect  At superconducting transition temperature, T c – Zero resistance – Meissner effect 3

Yttrium Barium Copper Oxide Superconductor  Chemical formula: YBa 2 Cu 3 O 7-x  Crystalline structure  T c : 95 K (Boiling point of liquid nitrogen 77 K)  Synthetic methods – Solid-state reaction – Sol-gel method – Co-precipitation Unit cell 4

Procedures of Solid-State Reaction Yttrium oxide, Y 2 O 3 Grind 930 o C, in air Barium Carbonate, BaCO 3 Copper(II) Oxide, CuO 10 h Press 1 ton/cm 2 YBa 2 Cu 3 O 7-x superconductor Atomic ratio Y : Ba : Cu = 1 : 2 : 3 5

Calculation of Formula To synthesize 0.004 mol YBa 2 Cu 3 O 7-x (Y : Ba : Cu = 1 : 2 : 3 ) Obtain: 1/2 × 0.004 × 225.82 = 0.4516  0.45 g Y 2 O 3 2 × 0.004 × 197.31 = 1.5785  1.58 g BaCO 3 79.55 = 0.9546  0.95 g 3 × 0.004 × CuO * The stochiometric amount of starting materials is critical to the success of the experiment! 6

Grind and Mix the Reactants Still contains white powder  Use agate mortar ( NTD 9,000~15,000 )  Mix chemicals with plastic spatula first, then grind  Grind until color appears gray and homogeneous, that may take about 10~15 min.  Collect the ground powder in a piece of weighing paper 7

Pressing － Hydraulic Press and Dies Parts of dies Pressure gauge Hollow ring Hydraulic press 8

Setup and Procedures of Pressing Place weighing Rotate the die left to Place the dies on Transfer powder paper underneath right to even up center of hydraulic into die the die powder plateform Release the valve Fix the dies in Close the valve Apply the pressure to counter- position 1 ton/cm 2 for 1 min. 9 clockwise clockwise

Setup and Procedures of Obtaining Pellet sample • Close the valve clockwise • Release the valve Hollow • Pull leverage to surface the • Take out the hollow ring ring superconductor pellet Dies with sample Sample Cylinder • Place the dies in center of plateform upside down Resulting sample Place pellet on to an alumina plate • Setup the hollow ring and pellet with plastic tweezers carefully 10 leveling surface

Sintering at 930 o C  The box furnace can hold 4 × 4 = 16 samples  Alumina plate cannot be labeled, record the position in furnace instead  Sinter the samples at 930 o C for 10 h. by raising and lowering the temperature at a rate of 5 o C/min. 11

Examine the Meissner Effect － Levitation of Magnets  Place superconductor in petri dish  Pour in liquid nitrogen and immerse the superconductor  Place magnetic bars on superconductor pellet with plastic tweezers, compare levitation height and amount of magnetic bars  Notice that the magnetic bars are small and easily lost  Dry and warm the superconductor with a hair dryer to room temp. 12

Design Your Superconductors as a Souvenir 5.0 cm 3.5 cm 13

Notice Condensed report  The dies should be placed in center of platform to prevent uneven application of pressure when pressing  Pressure should be kept at 1 ton/cm 2 for 1 min.  Clean up the dies thoroughly after each use to avoid the powders pile up in dies and cause it to get stuck  Avoid direct contact with liquid nitrogen which may cause frostbite 14