Mercury as Relativistic Charge Donor in A15 Vanadium-Titanium Superconductors: A Novel Ternary Compound Prediction

Abstract. We report a computational search for A15-structured vanadium-titanium superconductors in which mercury acts as a minority electronic dopant. Building on our companion paper (Fenning, 2026b), which identified V0.75Ti0.12Ga0.06Sn0.07 as the highest-Tc compound predicted from the Cardone element set (Tc = 21.69 K), we now extend the search to include mercury as a dopant element. Mercury is not treated as a bulk constituent but as a minority charge-reservoir species (xHg = 2–5%), motivated by the relativistic contraction of the Hg 6s orbital — the same quantum-mechanical effect that makes mercury cuprates the record holders for ambient-pressure Tc. A three-stage autonomous engine (HTC+Hg, 28 parallel workers, 600 trials per seed) searches the full Cardone composition space with Hg as a free variable. The top result, V0.75Ti0.22Hg0.03, is predicted at Tc = 22.36 K, a +0.67 K improvement over the Hg-free benchmark. All predicted compounds are confirmed absent from the Supercon2 database of 29,053 known superconductors. No Hg-V or Hg-Ti system of any composition appears in the database. The Hg enhancement is modest but physically motivated and experimentally testable. The optimal Hg fraction (xHg ≈ 0.033) is precisely predictable from the Gaussian peak model of N(EF) enhancement, and falls sharply beyond xHg = 0.06. Synthesis route and measurement protocol are proposed.