This work was performed under the guidance of Prof. T. A. Tyson at the New Jersey Institute of Technology. The research was sponsored by the ACS Project SEED (S. R. Farenholtz) and supported in part by ACS Petroleum Research Fund Grant 31750-G5 and National Science Foundation Grant DMR 9733862.

Superconductivity is the complete disappearance of electrical resistance in various solids when they are cooled below their critical temperature. A solid’s superconducting critical temperature is the point at which it no longer has resistance to electron flow. In order to reach this state three conditions must be met: the temperature must be below the critical temperature, the magnetic field must be less than the critical magnetic field and the current density must be less than the critical current density. If any of these three values is exceeded in some way the material loses its superconductivity.

Electric current in a wire creates magnetic fields around the wire itself. Superconductors can carry large currents without loss of energy. If the magnetic field generated around the superconductor gets too large it will cancel it’s own superconductivity. The maximum value for the magnetic field that can be sustained by the superconductor at any given temperature is the critical magnetic field. Since the current in the superconductor creates it’s own magnetic field, if that current flow gets too high it is possible for the superconductor to revert back to revert to it’s normal state. The critical current density is the maximum value of current that can flow through a superconductor before it becomes normal.

DISCOVERY OF SUPERCONDUCTORS

Superconductivity was discovered by Hike Kamerlingh Onnes, in Holland, in the year 1911 while he was investigating helium gas liquification. As chair of experimental physics at the University of Leiden, he investigated the electrical resistance of metals at low temperatures. Onnes investigated the resistivities of gold and platinum, but their resistance leveled off at extremely low temperatures due to impurities. He decided to use mercury which could be distilled and purified to a much better degree than platinum or gold. He found that the electrical resistance of mercury dropped to zero at 4 Kelvin. He received the 1913 Nobel Prize in Physics for his discovery.

The original elemental superconductors such as mercury, aluminum and zinc are classified as type I superconductors. They have one critical magnetic field for any given temperature. In 1957 a soviet physicist Alexi Abrikov found that there are type II superconductors which have slightly different properties. Type II superconductors have two critical magnetic fields. When a magnetic field is weaker than the first magnetic field they exhibit the same properties as type I superconductors. If the magnetic field is larger than the second critical magnetic field they behave like normal metals. However, if the magnetic field has a value between the two critical magnetic fields, they have zero resistance as well as partial flux penetration: something type I superconductors are not capable of doing. Type II superconductors are alloys and compounds, except niobium and vandium. When a magnetic field is between the two critical magnetic fields, the type II superconductor is said to be in the vortex state. In the vortex state there are several cores of normal material surrounded by superconductive material. As the magnetic field increases the vorticies in the superconductor increase until no more can be held and the superconductor returns back to it’s normal state.

Metals with low resistance at room temperature such as cooper, silver and gold are not superconductors while metals with high resistance at room temperature such as mercury, lead and tin are. This is so because of the lattice vibrations inside their structures. When a material is warm, the lattice vibrates randomly because of the thermal

energy. The more rapid the lattice vibrates, the more electrons traveling through them will be slowed down because of scattering from the vibrating atoms. Easy vibrating material usually have higher resistance while materials which do not, usually have low resistance at very low temperatures. Pairs of electrons can move through materials in which the lattice vibrates more easily. In 1986, materials that where insulators at room temperature were found to be superconductors. They have higher critical temperatures (some exceeding the boiling point of liquid nitrogen ) than older superconductors and are referred to as high temperature superconductors.

The first high temperature superconductor was discovered by Karl Alex Muller and Johannes George Bednorz in 1986 Zurich, Switzerland. Until than Nb₃Ge had the highest critical temperature of 23 Kelvin. A sample of lanthanum barium copper oxide was produced by Claude Michel L.E.-Rahko and Bernard Raveau in France. Muller and Bednorz saw its superconductive capabilities and soon made their own. Its critical temperature came out to be around 30 Kelvin. Many researchers worldwide began investigating superconductivity in perovskites, in search of a room temperature superconductor.

The new ceramic superconductors are a collection of minerals called perovskites. Perovskites are metal oxides, which exhibit a stoichiometric ratio of 3 oxygen atoms for every 2 metal atoms. They are commonly mixtures of many different metals. Since perovskites are ceramics and share many of their properties, perovskites tend to be very brittle. This has made them very hard to work with in applications such as wire. The perovskite structure is named after the mineral CaTiO₃ this structure is made up of corner sharing TiO₆ octahedra with Ca ions in the huge holes at the corners of the unit cell.

In 1987, a research group led by C.W. Paul Chu discovered a compound that superconducted above the boiling point of nitrogen. They used a yttrium substitute for lanthanum in a 1:2:3 ratio with barium and copper. The critical temperature was 90 Kelvin while the boiling point of nitrogen is 77 Kelvin. Liquid nitrogen is easier to obtain and cheaper than liquid helium. There are critical temperatures around 150 Kelvin today as the search for a room temperature superconductor continues.
 
 

The understanding of superconductivity is extremely complicated and involved.The ability of electrons to pass through superconducting material freely has puzzled scientist for many years. In 1957 three physicist John Borden, Leon Cooper and John Schrieffer developed a phenomenoligical model which earned them a Nobel prize. Atomic lattice vibrations directly unify the entire current. They force electrons to pair up into teams to pass the obstacles which cause resistance. The pair of electrons is known as the Cooper pair. When an electron passes the lattice it gets distorted. Before the electron can pass by and the lattice return to normal another electron comes and interacts with the first electron ( which despite its negative origin received an aura of positive energy from the distorted lattice ). Superconductors also exhibit a repulsive force known as the Meissner effect. Superconductors repel magnetic fields from. A light powerful magnet can be suspended by a supercoductor below its critical temperature. This is a very common demonstration of superconductivity.

In 1962, Brian Josephson found it was possible for electron pairs to go through a thin insulating barrier without resistance. The current that flows has a critical current density which is similar to that of the material. A Josephson junction consist of two superconductors separated by a thin insulator. As long as the current is below the critical current, there will be zero resistance and no voltage drop across the junction. The Josephson junction is a superfast switching device. It can switch voltages in a computer, which depends on short, on-off electrical pulses. Computers speed is dependant on the time required to transmit signal pulses and the Josephson junction supplies exceptional switching speed for use in superfast, smaller computers.

After Kamerlingh Onnes discovered superconductivity many scientist started to think of applications. Powerful new superconducting magnets could replace the much larger resistive magnets. Generators could generate electricity with smaller equipment and less energy. Energy could be stored for long periods of time without loss in superconductive coils. Current applications of high temperature superconductors includes : magnetic shielding, S.Q.U.I.Ds, infrared sensors, medical imaging and microwaves. With our growing understanding of superconductors we may be able to make such things as : power lines, energy stores, particle accelerators and levitating vehicles seem possible.

There are two standard methods of preparing a superconductor: the solid-state reaction method and the coprecipitation method. In the solid-state reaction method, oxide or carbonate forms of constituents are mixed and ground over several times and then placed in the furnace the heat and cool. This somewhat more appealing to scientist because it is relatively quick. The coprecipitation method starts with the nitrate forms of the constituents, which are precipitated out of solution in their corresponding carbonate forms. The sludge is then heated to remove water. The advantage of the coprecipitation method is the constituents are mixed on the atomic level. This avoids contamination.

Recently I had the opportunity to make a commonly known superconductor by the name of Yttrium Barium Copper Oxide (YBa₂Cu₃O₇) or the 1-2-3 superconductor. Its name comes from the stoichiometric ratio of elements to on another. First I made sure the contents of the containers were the ones being used. You must weigh out the exact amount of elements being used (it is highly suggested that you sterilize the spatula with Acetone between each weighing). All the compounds are placed in a sealable jar and shaken for approximately fifteen minutes until a semi-homogeneous mixture is attained. The main purpose of the shaken is to thoroughly mix the starting compounds. Before grinding it is ideal to wash out the mortar and pestle with some Acetone. In the 30 minute grinding process the goal is to reduce the grain size and mix the powder leaving it a uniform gray color. The compound is placed in an Al₂O₃ mold (referred to by many as a "boat") and heated in a furnace for eighteen hours at nine hundred forty degrees Celsius and slowly cooled to room temperature. After the compound is removed, if there are any

green colored particles, the compound must be reground and heated again because the green color indicates nonsuperconducting material typically copper oxide. This process is repeated as many times as necessary until the compound can be tested in its uniform gray color.

Sir William Lawrence Bragg a British physicist and Nobel prize winner, won the nobel prize in physics along with his father, for their work in establishing x-ray crystallography. Bragg discovered that certain planes in a crystal reflect x-rays, in accordance with the normal law of reflection. The distance between parallel planes of atoms determines the angle at which reflection can take place for a certain wavelength of the x-rays. This relation, known as Bragg’s law permits scientist to measure the wavelengths of the x-rays and determine the structure of complex compounds.

While applications are at varying levels of development, the technological landscape is already being reshaped by new superconductors. We look forward to the discovery of room temperature superconductors. They will significantly impact our lives.
 
 

We thank professor T. A. Tyson of NJIT for his support as a mentor. This project was funded in part by National Science Foundation grant DMR9733862.
 
 

http://www.cm.utexas.edu/~mcdevitt/Links/Superconductor.html

http://www.ornl.gov/reports/m/ornlm3063r1/contents.html

http://www.uq.oz.au/nanoworld/precpowd.html

http://www.uq.oz.au/nanoworld/htsc.html

http://www2.csn.net/~donsher/

http://beca.ece.jcu.edu.au/ece/staff/jana/r.htm

http://neon.chem.ox.ac.uk/vrchemistry/super/default.html

http://www.aip.org/

http://www.superconductorweek.com/

http://www.conductus.com/supercon.htm

http://www.eapen.com/jacob/superconductors/chapter5.html

http://www.au.af.mil/own/sandt/supercon.html

http://www-personal.umich.edu/~jshaver/virtual/labeled/

http://astsun.astro.virginia.edu/~eww6n/physics/RamanSpectroscopy.html

http://www.iumsc.indiana.edu/xray.htm

http://www.kfki.hu/~szfkihp/labs/xrdlab.html
 
 
 
 
 
 
 
 

X-Ray Diffraction Pattern from Published Work

Physical Review Letter, 58 1676 (1987).

H K L D I/Io

1 0 3 2.726 100

1 1 0

0 1 3 2.750 60

1 2 3 1.584 24

1 1 6

0 2 0 1.946 23

0 0 6

1 1 3 2.232 13

0 0 3 3.893 11

0 0 5 2.336 11

2 1 3 1.569 11

2 0 0 1.911 10

1 0 2 3.198 5

1 0 0 3.822 3

0 1 2 3.235 3

1 1 2 2.469 3

1 0 4 2.321 3

1 1 5 1.775 3

0 0 2 5.844 2

1 1 1 2.653 2

0 1 6 1.741 2

0 2 3

2 1 0 1.716 2

1 2 1

1 2 2 1.662 1
 
 

NEVIS>TYPE C4.C

# include <stdio.h>

# include <math.h>

/* ybco index generation */

main()

{

int i,j,k,end;

float a,b,c,lam,d,t1,t2,t3,t,tth,fact;

i=0;

j=0;

k=1;

lam=1.54056;

a=3.8218;

b=3.8913;

c=11.677;

fact=57.2958;

end=3;

while (i <= end)

{

while (j <= end)

{

while (k <= end)

{

t1=i/a;

t1=t1*t1;

t2=j/b;

t2=t2*t2;

t3=k/c;

t3=t3*t3;

t=t1+t2+t3;

d=sqrt (1.0/t);

tth=fact*2.0*asin(lam/(2.0*d));

printf("%d %d %d %f %f\n",i,j,k,tth,d);

k=k+1;

}

k=0;

j=j+1;

}

j=0;

i=i+1
 
 
 
 

OUTPUT OF C4 Program

NEVIS>RUN C4

0 0 1 7.564593 11.677000

0 0 2 15.162406 5.838500

0 0 3 22.827991 3.892334

0 1 0 22.834135 3.891300

0 1 1 24.086664 3.691709

0 1 2 27.523615 3.238022

0 1 3 32.509125 2.751930

0 2 0 46.644070 1.945650

0 2 1 47.326042 1.919191

0 2 2 49.328835 1.845855

0 2 3 52.540375 1.740335

0 3 0 72.861107 1.297100

0 3 1 73.382195 1.289171

0 3 2 74.937210 1.266228

0 3 3 77.504509 1.230570

1 0 0 23.255121 3.821800

1 0 1 24.487322 3.632206

1 0 2 27.878120 3.197646

1 0 3 32.814480 2.727016

1 1 0 32.818882 2.726660

1 1 1 33.727764 2.655232

1 1 2 36.334042 2.470525

1 1 3 40.353703 2.233221

1 2 0 52.750690 1.733890

1 2 1 53.374542 1.715086

1 2 2 55.216805 1.662143

1 2 3 58.199841 1.583850

1 3 0 77.675682 1.228285

1 3 1 78.185593 1.221546

1 3 2 79.709831 1.201974

1 3 3 82.234505 1.171347

2 0 0 47.544006 1.910900

2 0 1 48.216267 1.885816

2 0 2 50.192368 1.816103

2 0 3 53.366264 1.715332

2 1 0 53.369240 1.715244

2 1 1 53.988125 1.697033

2 1 2 55.816570 1.645695

2 1 3 58.779732 1.569599

2 2 0 68.804443 1.363330

2 2 1 69.338303 1.354132

2 2 2 70.928940 1.327616

2 2 3 73.547157 1.286686

2 3 0 91.735588 1.073210

2 3 1 92.234528 1.068706

2 3 2 93.732521 1.055526

2 3 3 96.235390 1.034603

3 0 0 74.406921 1.273933

3 0 1 74.923973 1.266419

3 0 2 76.467796 1.244649

3 0 3 79.019363 1.210735

3 1 0 79.021790 1.210704

3 1 1 79.529305 1.204249

3 1 2 81.047012 1.185484

3 1 3 83.563080 1.156070

3 2 0 92.560143 1.065797

3 2 1 93.059387 1.061385

3 2 2 94.558655 1.048471

3 2 3 97.064934 1.027957

3 3 0 115.881248 0.908887

3 3 1 116.436790 0.906146

3 3 2 118.119949 0.898070

4.2 K 1911 Hg

23 K 1973 Nb₃Ge

35 K 1986 LaBaCuO₄

92 K 1986 YBa₂Cu₃O₇

110 K 1987 NiCaSrCu₂O₉

125 K 1988 TISrBaCuO

133 K (up to 160 K 1993 HgBa₂Ca₂Cu₃O₈

under pressure)

High temperature superconductors are material which conduct electricity without resistance at much higher critical temperature than earlier superconductors- typically above the temperature of liquid nitrogen. Our goal was to learn more about these materials and finally make our own high temperature superconductor, YBa₂Cu₃O_6+x (YBCO).

Some Critical Temperatures of Superconducting Materials

4.2 K 1911 Hg

23 K 1973 Nb₃Ge

35 K 1986 LaBaCuO₄

92 K 1986 YBa₂Cu₃O₇

110 K 1987 NiCaSrCu₂O₉

125 K 1988 TISrBaCuO

133 K (up to 160 K 1993 HgBa₂Ca₂Cu₃O₈

under pressure)

There were many instruments used in our synthesis of a high temperature superconductor. Primarily a furnace was used because of the 950° C needed to heat the sample. We utilize the solid-state reaction method of the synthesis in which the starting materials were weighed, mixed thoroughly and ground with a mortar and pestle until our sample was a uniform gray color. The sample was then heated in an Al₂O₃ boat. The sample was ground and reheated several times. Finally, the sample was ground pressed into a pellet for testing.

We prepared approximately 30 grams of YBCO in our experiment. We had to determine the exact amount of each compound to use. The solid phase reaction is based on the following equation:

0.5Y₂O₃ + 2BaCO₃ + 3CuO à YBa₂Cu₃O_6+x + 2CO₂

C,O are remove as gasses. They are not accounted for in balancing the equation. To produce 30 grams of YBCO we calculated the required amounts of starting materials (see left side of above equation)

Determination of the Molecular Weight of YBCO

YBa₂Cu₃O₇

1(88.9059) = 88.9059

2(137.33) = 274.66

3(63.546) = 190.638

7(15.9994) = 111.9958

666.1997 grams/mole

30g of YBCO = 0.0450315 moles of YBCO

666.1997 g/m

Determination of the Required Weight of Y₂O₃

2(88.9059) = 177.8118

2

Determination of the Required Weight of BaCO₃

Determination of the Required Weight of CuO

During our project we used an x-ray diffractor and a raman spectrum to determine if our sample was pure or not. The x-ray diffractor showed our sample was very similar to a pure one (see chart of d-space and intensity measurements). The Raman Spectrum was not inconclusive. However, the Meissiner was positive.

We knew our sample was pure when we tested it for the Meissner effect. The Meissner Effect is the phnomenon where a superconductor expels all magnetic fields. A light powerful magnet will then float above the superconductor if the temperature of the superconductor is below its Critical temperature. Our sample was chilled using liquid nitrogen and as soon as it reached its critical temperature the magnet began to float above the superconductor pellet. This proved definitively that we had synthesized YBCO.

Application Current Emerging

Medical

Magnetic resonance image x

Biotechnical engineering x

Electronics

SQUIDs x

Transistors x

Josephson Junction devices x

Circuitry connections x

Particle accelerators x

Sensors x

Industrial

Separation x

Magnets x

Sensors and transducers x

Magnetic shielding x

Power Genaeration

Motors x

Generators x

Energy Storage x

Transmission x

Fusion x

Transformers and Inductors x

Transportation

Magnetically levitated vehicles x

Marine propulsion x

A large number of possible applications exist. High temperature superconductors hold the promise to impact our everyday lives significantly.

Bc(T) = Bc(0k) [ 1 – (T/Tc)^2]

Critical Magnetic field

Tc = (k/M)^alpha

Critical temperature on an isotope :

k = constant, M = isotopic mass,

alpha = isotope-effect exponent

After our work was completed we successfully made our high temperature superconductor. However, our Raman spectrum was inconclusive due possible to low signal or equipment failure. Our final test of the Meissner effect was the definitive test. During the test a small magnet levitaed over our superconductor.

Our experience during this summer here was enlightnen. We learned of a product which can save a lot of money and got the opportunity to make one first hand. Superconductors can be used in a wide variety of ways. We both had a wonderful time creating something so powerful and helpful to everyone.