NOVELTY - An Hg-containing superconductor is obtained by annealing a body of a substrate and a Tl-based superconducting film in Hg vapor to replace at least some Tl with Hg. Thermoelectric material having ZT at least 2 is formed by replacing a first molecule bonded to an atom in a crystalline precursor having a crystal lattice with a second molecule.    USE - Superconducting and thermoelectric materials.    ADVANTAGE - The superconducting films have a high degree of epitaxy and correspondingly high Tc and Jc values. The thermoelectric materials have an improved figure of merit, ZT.    DETAILED DESCRIPTION - Production of an Hg-containing film superconductor comprises:    (a) providing a body comprising a substrate having a Tl-based superconducting film, selected from Tl-1212, Tl-2212, Tl 1223 and Tl 2223 films, supported on its surface; and    (b) annealing the body at 600-900 degrees C for 1-20 hours in the presence of Hg vapor under conditions whereby at least a portion of the Tl of the superconducting film is replaced by Hg to form a 0.005-500 microns thick Hg-containing film selected from Hg 1212 (HgBa2CaCu2Ox; x = 5.8-6.2) and Hg 1223 films having a Jc of at least 106 A/square cm at 100K and zero magnetic field, a Xmin of up to 50%, and microwave surface resistance less than about 0.4 mOhm at 120K.    At least part of the Tl-based superconducting film can be removed to form bridges prior to annealing.    An INDEPENDENT CLAIM is given for a method of forming a thermoelectric material having a ZT of at least 2, where a three-dimensional, crystalline precursor, preferably a body-centered crystal of a skutterudite containing Fe, Ru, Os, P, As and Sb atoms, comprising a number of atoms presenting a crystal lattice and a first molecule, selected from La, Ce, Pr, Nd and Eu, bonded to at least one of the atoms is perturbed by heating to at least 800 degrees C to release a first molecule from the precursor, and the precursor is contacted with a vapor comprising a second molecule, selected from Pb, Hg, Sn, In, Tl and Ga, so that the second molecule replaces the first molecule in the precursor.