High-Tc ceramics: superconducting transition range Some ceramic (oxide) materials become superconducting in which temperature range?

Introduction / Context:
High-temperature superconductors (HTS), notably cuprate ceramics like YBCO and BSCCO, revolutionized superconductivity by exhibiting critical temperatures well above liquid nitrogen’s 77 K, enabling more practical cryogenic systems than liquid helium cooling.

Given Data / Assumptions:

• Liquid helium ~4.2 K, liquid nitrogen ~77 K, room temperature ~300 K.
• HTS ceramics exhibit Tc in the range ~90–135 K (typical).

Concept / Approach:

While conventional metallic superconductors have Tc below 20 K, certain oxide ceramics transition to the superconducting state at temperatures exceeding 77 K. Thus they lie “above liquid nitrogen but below room temperature,” enabling nitrogen-based cooling approaches in power cables, magnets, and electronics.

Step-by-Step Solution:

Verification / Alternative check:

Empirical Tc tables for cuprate families consistently exceed 77 K but remain far below 300 K.

Why Other Options Are Wrong:

A applies to conventional low-Tc metals; B underestimates HTS Tc; D/E are incorrect as no stable bulk ceramic superconductor operates at room temperature presently.

Common Pitfalls:

Assuming “high-temperature” means room temperature; overlooking cryogenic reference points.

Final Answer:

above liquid nitrogen but below room temperature