A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-0 compound system at ambient pressure. An estimated upper critical field H, 2(0) between 80 and 180 T was obtained.

1ft 'J .Ó AP E418 Superconductivity ExperimentS uperconductivity may beome one of the most signifcant inovations of mom times. Ths is a result of very recent discoveries of high temperature superconductorswhich may revolutionize everything from electrcal generation and transmission to high-speed cQmputers to controlled fusion generatig plants.In ths experiment, you will investigate the superconductivity of the new Y -Ba-Cu-O compound system as a function of temperature and magnetic field. The most important question should should answer is "What is the resistance of the superconductor as the temperatu and applied magnetic field ar changed?" Other questions which you wil not be able to answer are related to the determination of curent density which can pass through the material and the mechanical strength and elasticity of the material.Attached to these notes are some articles which describe aspects of superconductivity and the results of recent measurements of the Y -Ba-Cu-O compound made by Prof. M. K. Wu and co-workers. These wil provide background for the experiments that you wil be penormg. Pay paricular attention to Prof. Wu's aricle. Their measurements are identical to those that you can obtan with the equipment supplied in the laboratory. Next, look over the description of tye 1 and j , ty.e 2 superconductors given by Gennes in Superconductivity in Metals and Alloys.o.f\1. , l' -Type 1 superconductors have a "correlation length" between. conduction electrons ((sheri (denoted by the symbol, ÇO) much longer than the magnetic field penetration length ( denoted by Â.). They generally have a very abrupt crtical field, He, below which the P-i1lèt material is superconducting and excludes all magnetic flux. (H e is a function of temperature.) This "penect diamagnetîsm" is charaèteristic of the superconducting state. Type 2 superconductors have Â. ~ Ço and have a more gradual transition to this superconducting state. They are described by thee critical magnetic fields. Below Hci (the lowest critical field), a typ 2 superconductor has no resistace and, like a type 1 superconductor, excludes flux. Between H c1 and H e2, the resistance is very low, but finite, and the superconductor parally excludes flux. Between He2 and He3, the resistance is low, but no flux is excluded. Finally, above the highest of the three crtical fields, He3. the material is no longer superconducting. DescrI ptionThe Y -Ba-Cu-O compound becomes superconducting between 77 and 85 eK.This makes the cryogenic aspects of these experiment very easy compared with experiments using more conventional superconductors that require temperatures below 22 eK. Liquid nitrogen is relatively inexpensive and a styrofoam thermos is al that is required to store it for several hours.-We have built three LN2 containers for you, and these are large enough to hold stainless-steel and copper "sample stands". The sample stands cool the 1 \, W£t.~ i-superconducting sample and provide a stable base to make your measurements. Also, attached to each sample is a calibrated t...

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Thin C:N films were prepared by rf diode sputtering of a graphite target in a mixed argon/nitrogen plasma. We have observed a systematic variation of the properties of these C:N films with an increase in the nitrogen partial pressure. XPS, AES, and TEM studies show that nitrogen will stabilize the diamond sp3 bonding. From XPS studies, we found that the density of our C:N films is increased from 1.37 × 1023 atoms/cm3 to 1.63 × 1023 atoms/cm3 using a 100% nitrogen plasma. The energy gap of our nitrogen carbon also shows an increase from 1.1 eV to 1.4 eV using a 100% nitrogen plasma. The mechanical properties also are shown to be enhanced for certain applications. By using the same method, we can also show that it can produce 100% amorphous C:N films which are more diamond-like as compared with other methods.

Immiscible GaBi alloys were solidified during free fall in the Marshall Space Flight Cente4 drop tower which provides about 4.5 seconds of low gravity (about 10−4 g, g = 980 cm/s2 ). We have measured the electrical resistivity and magnetic susceptibility as a function of pressure (up to 18 kbar) and temperature (300K to 4.2K) of drop tower (DT) sample and ground control (GC) sample prepared under identical conditions except for gravity. At ambient pressure the electrical resistance of the DT sample exhibits a broad maximum at 100K, while that of GC sample decreases rapidly as temperature decreases. Both DT and GC samples becomesuperconducting at 7.7K (Tc2). However, a minor second superconducting phase with a transition temperature at 8.3K (Tc1) is observed only in the DT samples.

Carbon thin films, were prepared by RF diode sputtering of a graphite target in an mixture of nitrogen and argon plasma. A series of carbon thin films was deposited as a function of nitrogen partial pressure and on different substrates. We observed a systematic variation of film properties with increasing nitrogen partial pressure which suggests that nitrogen will stabilize the diamond sp3 bonding in the films. The friction coefficient is also reduced as the nitrogen partial pressure is increased. For films prepared at low nitrogen partial pressure, the friction coefficient is 0.4. At higher nitrogen partial pressure, the friction coefficient reduced to the steady state value of 0.2.