Converting Hg-1212 to Tl-2212 via Tl–Hg cation exchange in combination with Tl cation intercalation

Abstract

In a cation exchange process developed recently for epitaxy of HgBa 2 CaCu 2 O 6 (Hg-1212) thin films, TlBa 2 CaCu 2 O 7 (Tl-1212) or Tl 2 Ba 2 CaCu 2 O 9 (Tl-2212) precursor films were employed as the precursor matrices and Hg-1212 was obtained by replacing Tl cations on the precursor lattice with Hg cations. The reversibility of the cation exchange dictates directly the underlying mechanism. Following our recent success in demonstrating a complete reversibility within '1212' structure, we show the conversion from Hg-1212 to Tl-2212 can be achieved via two steps: conversion from Hg-1212 to Tl-1212 followed by Tl intercalation to form double Tl-O plans in each unit cell. The demonstrated reversibility of the cation exchange process has confirmed the process is a thermal perturbation of weakly bonded cations on the lattice and the direction of the process is determined by the population ratio between the replacing cations and that to be replaced.

Superconductivity of 132 K in HgBa2Ca2Cu3O8+δthin films fabricated using a cation exchange method

“…Using epitaxial Tl-1212 and Tl-2212 films as precursors, epitaxial Hg-1212 thin and thick films have been obtained on dielectric and metal substrates for both electronic [12][13][14][15][16] and electrical devices applications [17,18]. Furthermore, the cation exchange between Hg-1212 films and Tl-1212 (or Tl-2212) films has been found to be fully reversible [10,19].…”