Ceramic Problems/Challenges in High Temperature Oxide Superconductors; Hysteretic Force Measurements As a New Analysis Tool
Increasing realism that high temperature oxide superconductors have many unusual and difficult aspects is setting in. It is becoming apparent that many of the problems/challenges are directly dependent upon the ceramic-like properties of these materials, when in polycrystalline form, and that many of these have been encountered before in other ceramic guises. We originally guessed, without making hundreds of specimens, that the peculiar R/T double step (with one drop at ~ 100K, and a second drop at ~ 85K) in the Bi HTSC and the inability initially to get R = 0 at > 100K came about through syntactic (coherent) intergrowths [1,2] which are so well known in minerals . We therefore disagree with many ideas that have been put forward to explain this phenomenon [3–12]. We will show that problems with the Bi containing superconductors are extreme to the point where our personal decision is to abandon work on their polycrystalline forms in favor of Tl materials, at least for the time being. We prefer to make bad ceramics of a 125K material than of a 90K variety for obvious reasons. Space applications, where passive cooling, with attendant weight saving and increased robustness, are our major incentive.
KeywordsHall Probe Passive Cool Polycrystalline Form Flash Heating Single Crystallite
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