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39 records · Page 3

Low Current and Analog Memristor with Ru as Mobile Species

The switching parameters and device performance of memristors are predominately determined by their mobile species and matrix materials. Devices with oxygen or oxygen vacancies as the mobile species usually exhibit a great retention but also need a relatively high switching current (e.g., >30 mu A), while devices with Ag or Cu as cation mobile species do not require a high switching current but usually show a poor retention. Here, Ru is studied as a new type of mobile species for memristors to achieve low switching current, fast speed, good reliability, scalability, and analog switching property simultaneously. An electrochemical metallization-like memristor with a stack of Pt/Ta2O5/Ru is developed. Migration of Ru ions is revealed by energy-dispersive X-ray spectroscopy mapping and in situ transmission electron microscopy within a sub-10 nm active device area before and after switching. The results open up a new avenue to engineer memristors for desired properties.

analog switching↗

Materials Data on Ho20Cu6(Pb3S14)3 by Materials Project

Ho20Cu6(Pb3S14)3 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are twenty inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, corners with two PbS7 pentagonal bipyramids, edges with five HoS6 octahedra, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 3–41°. There are a spread of Ho–S bond distances ranging from 2.70–2.80 Å. In the second Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, a cornercorner with one HoS7 pentagonal bipyramid, a cornercorner with one PbS7 pentagonal bipyramid, edges with five HoS6 octahedra, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 2–39°. There are a spread of Ho–S bond distances ranging from 2.71–2.75 Å. In the third Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, edges with five HoS6 octahedra, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 2–38°. There are a spread of Ho–S bond distances ranging from 2.70–2.77 Å. In the fourth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, a cornercorner with one HoS7 pentagonal bipyramid, edges with five HoS6 octahedra, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 7–38°. There are a spread of Ho–S bond distances ranging from 2.71–2.77 Å. In the fifth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, edges with five HoS6 octahedra, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 6–40°. There are a spread of Ho–S bond distances ranging from 2.71–2.77 Å. In the sixth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, edges with five HoS6 octahedra, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 2–41°. There are a spread of Ho–S bond distances ranging from 2.70–2.78 Å. In the seventh Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with two HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, edges with two HoS6 octahedra, an edgeedge with one HoS7 pentagonal bipyramid, edges with two PbS7 pentagonal bipyramids, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 41–48°. There are a spread of Ho–S bond distances ranging from 2.67–2.75 Å. In the eighth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with two HoS6 octahedra, a cornercorner with one HoS7 pentagonal bipyramid, edges with two HoS6 octahedra, an edgeedge with one HoS7 pentagonal bipyramid, an edgeedge with one PbS7 pentagonal bipyramid, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 38–63°. There are a spread of Ho–S bond distances ranging from 2.69–2.82 Å. In the ninth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with two HoS6 octahedra, a cornercorner with one HoS7 pentagonal bipyramid, a cornercorner with one PbS7 pentagonal bipyramid, edges with two HoS6 octahedra, edges with two PbS7 pentagonal bipyramids, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 40–50°. There are a spread of Ho–S bond distances ranging from 2.66–2.78 Å. In the tenth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with two HoS6 octahedra, edges with two HoS6 octahedra, an edgeedge with one HoS7 pentagonal bipyramid, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 41–55°. There are a spread of Ho–S bond distances ranging from 2.64–2.81 Å. In the eleventh Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with two HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, edges with two HoS6 octahedra, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 39–56°. There are a spread of Ho–S bond distances ranging from 2.64–2.80 Å. In the twelfth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with two HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, edges with two HoS6 octahedra, an edgeedge with one PbS7 pentagonal bipyramid, and edges with two CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 38–57°. There are a spread of Ho–S bond distances ranging from 2.70–2.77 Å. In the thirteenth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, corners with three PbS7 pentagonal bipyramids, a cornercorner with one CuS4 tetrahedra, edges with five HoS6 octahedra, and an edgeedge with one HoS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 2–48°. There are a spread of Ho–S bond distances ranging from 2.68–2.77 Å. In the fourteenth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, corners with two equivalent HoS7 pentagonal bipyramids, a cornercorner with one CuS4 tetrahedra, and edges with five HoS6 octahedra. The corner-sharing octahedra tilt angles range from 4–63°. There are a spread of Ho–S bond distances ranging from 2.69–2.83 Å. In the fifteenth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, a cornercorner with one HoS7 pentagonal bipyramid, corners with two equivalent PbS7 pentagonal bipyramids, a cornercorner with one CuS4 tetrahedra, edges with five HoS6 octahedra, and an edgeedge with one PbS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 2–50°. There are a spread of Ho–S bond distances ranging from 2.66–2.80 Å. In the sixteenth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, a cornercorner with one HoS7 pentagonal bipyramid, a cornercorner with one CuS4 tetrahedra, and edges with five HoS6 octahedra. The corner-sharing octahedra tilt angles range from 7–55°. There are a spread of Ho–S bond distances ranging from 2.63–2.85 Å. In the seventeenth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, a cornercorner with one CuS4 tetrahedra, and edges with five HoS6 octahedra. The corner-sharing octahedra tilt angles range from 7–56°. There are a spread of Ho–S bond distances ranging from 2.62–2.85 Å. In the eighteenth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, a cornercorner with one CuS4 tetrahedra, edges with five HoS6 octahedra, and an edgeedge with one PbS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 3–57°. There are a spread of Ho–S bond distances ranging from 2.69–2.81 Å. In the nineteenth Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Ho–S bond distances ranging from 2.63–3.23 Å. In the twentieth Ho3+ site, Ho3+ is bonded to seven S2- atoms to form distorted HoS7 pentagonal bipyramids that share corners with eight HoS6 octahedra, a cornercorner with one CuS4 tetrahedra, edges with four HoS6 octahedra, and a faceface with one PbS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 23–70°. There are a spread of Ho–S bond distances ranging from 2.62–3.19 Å. There are six inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share a cornercorner with one HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, corners with two CuS4 tetrahedra, and edges with four HoS6 octahedra. The corner-sharing octahedral tilt angles are 10°. There are a spread of Cu–S bond distances ranging from 2.33–2.37 Å. In the second Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share a cornercorner with one HoS6 octahedra, corners with two CuS4 tetrahedra, and edges with four HoS6 octahedra. The corner-sharing octahedral tilt angles are 8°. There are a spread of Cu–S bond distances ranging from 2.29–2.37 Å. In the third Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share a cornercorner with one HoS6 octahedra, corners with two CuS4 tetrahedra, and edges with four HoS6 octahedra. The corner-sharing octahedral tilt angles are 10°. There are a spread of Cu–S bond distances ranging from 2.33–2.38 Å. In the fourth Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share a cornercorner with one HoS6 octahedra, corners with two CuS4 tetrahedra, and edges with four HoS6 octahedra. The corner-sharing octahedral tilt angles are 9°. There are one shorter (2.32 Å) and three longer (2.36 Å) Cu–S bond lengths. In the fifth Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share a cornercorner with one HoS6 octahedra, a cornercorner with one PbS7 pentagonal bipyramid, corners with two CuS4 tetrahedra, and edges with four HoS6 octahedra. The corner-sharing octahedral tilt angles are 10°. There are a spread of Cu–S bond distances ranging from 2.33–2.36 Å. In the sixth Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share a cornercorner with one HoS6 octahedra, a cornercorner with one HoS7 pentagonal bipyramid, corners with two CuS4 tetrahedra, and edges with four HoS6 octahedra. The corner-sharing octahedral tilt angles are 9°. There are one shorter (2.33 Å) and three longer (2.36 Å) Cu–S bond lengths. There are nine inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Pb–S bond distances ranging from 2.85–3.45 Å. In the second Pb2+ site, Pb2+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Pb–S bond distances ranging from 2.84–3.44 Å. In the third Pb2+ site, Pb2+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Pb–S bond distances ranging from 2.88–3.40 Å. In the fourth Pb2+ site, Pb2+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Pb–S bond distances ranging from 2.85–3.49 Å. In the fifth Pb2+ site, Pb2+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Pb–S bond distances ranging from 2.82–3.45 Å. In the sixth Pb2+ site, Pb2+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Pb–S bond distances ranging from 2.85–3.37 Å. In the seventh Pb2+ site, Pb2+ is bonded to seven S2- atoms to form distorted PbS7 pentagonal bipyramids that share corners with eight HoS6 octahedra, a cornercorner with one CuS4 tetrahedra, edges with four HoS6 octahedra, a faceface with one HoS7 pentagonal bipyramid, and a faceface with one PbS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 21–74°. There are a spread of Pb–S bond distances ranging from 2.84–3.24 Å. In the eighth Pb2+ site, Pb2+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Pb–S bond distances ranging from 2.83–3.24 Å. In the ninth Pb2+ site, Pb2+ is bonded to seven S2- atoms to form distorted PbS7 pentagonal bipyramids that share corners with eight HoS6 octahedra, a cornercorner with one CuS4 tetrahedra, edges with four HoS6 octahedra, and a faceface with one PbS7 pentagonal bipy

36 MATERIALS SCIENCE↗

Making Superconducting Welds between Superconducting Wires

A technique for making superconducting joints between wires made of dissimilar superconducting metals has been devised. The technique is especially suitable for fabrication of superconducting circuits needed to support persistent electric currents in electromagnets in diverse cryogenic applications. Examples of such electromagnets include those in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems and in superconducting quantum interference devices (SQUIDs). Sometimes, it is desirable to fabricate different parts of a persistent-current-supporting superconducting loop from different metals. For example, a sensory coil in a SQUID might be made of Pb, a Pb/Sn alloy, or a Cu wire plated with Pb/Sn, while the connections to the sensory coil might be made via Nb or Nb/Ti wires. Conventional wire-bonding techniques, including resistance spot welding and pressed contact, are not workable because of large differences between the hardnesses and melting temperatures of the different metals. The present technique is not subject to this limitation. The present technique involves the use (1) of a cheap, miniature, easy-to-operate, capacitor-discharging welding apparatus that has an Nb or Nb/Ti tip and operates with a continuous local flow of gaseous helium and (2) preparation of a joint in a special spark-discharge welding geometry. In a typical application, a piece of Nb foil about 25 m thick is rolled to form a tube, into which is inserted a wire that one seeks to weld to the tube (see figure). The tube can be slightly crimped for mechanical stability. Then a spark weld is made by use of the aforementioned apparatus with energy and time settings chosen to melt a small section of the niobium foil. The energy setting corresponds to the setting of a voltage to which the capacitor is charged. In an experiment, the technique was used to weld an Nb foil to a copper wire coated with a Pb/Sn soft solder, which is superconducting. The joint was evaluated as part of a persistent-current circuit having an inductance of 1 mH. A current was induced in a loop, and no attenuation of the current after a time interval 1,000 s was discernible in a measurement having a fractional accuracy of 10(exp -4): This observation supports the conclusion that the weld had an electrical resistance <10(exp -10) omega.

Penanen, Konstantin I.↗