40 degrees below zero is cold by any measure. But, in the world of superconductors it's a record hot day. Superconductors.ORG herein reports an increase in high-Tc to 233K (-40C, -40F) through the substitution of thallium into the tin/indium atomic sites of the X212/2212C structure that produced a 218 Kelvin superconductor in January of 2009.
The host material producing the 233K signal has the chemical formula Tl5Ba4Ca2Cu9Oy. One of several resistance-v-temperature plots used to confirm this new record is shown above. And a composite magnetization test, showing the Meissner transition, is shown below right.
Synthesis of these materials was by the solid state reaction method. Stoichiometric amounts of the below precursors were mixed, pelletized and sintered for 34 hours at 865C. The pellet was then annealed for 10 hours at 500C in flowing O2.
Tl2O3 99.99% (Alfa Aesar) 7.136 moles (gr.)
BaCuOx 99.9% (Alfa Aesar) 5.42 moles
CaCO3 99.95% (Alfa Aesar) 1.25 moles
CuO 99.995% (Alfa Aesar) 2.98 moles
The magnetometer employed twin Honeywell SS94A1F Hall-effect sensors with a tandem sensitivity of 50 mv/gauss. The 4-point probe was bonded to the pellet with CW2400 silver epoxy and used 7 volts on the primary.
Joe Eck also claims to have a version of YCBO that superconducts/has a Meissner Transition at 175K
92K YBCO (Y-123) has only 6 metal layers in the unit cell and very little PWD. In this new discovery - based on a 9223C theoretical structure type shown at left - there are 16 metal layers and a large amount of PWD. The closest analog to this structure type is the 9212/1212C intergrowth of the Sn-Ba-Ca-Cu-O family, with Tc ~195K.
The chemical formula of this new discovery - dubbed "Hyper YBCO" - is YBa3Cu4Ox. However, HY-134 does not form stoichiometrically. In order to synthesize a sufficent volume fraction to detect, the "layer cake" method must be used.
The layer cake used to produce the prototype pellet had 17 layers, 9 of (BaCuO) and 8 of (Y2O3 + CuO). This resulted in 16 interference regions in which the desired structure was encouraged to form. The layer cake method is depicted in the simplified graphic below.