Electrodeposition of Pt_(100-x)Pb_(x) Metastable Alloys and Intermetallics
Sun M. Hwang, John E. Bonevich, Jae Jeong Kim, Thomas P. Moffat
The electrodeposition of a series of metastable Pt-Pb alloys and intermetallic phases as well as elemental Pt is demonstrated using an acid electrolyte comprised of 0.05 mol/L Pb(ClO_4)_2 and/or 0.001 mol/L K_2PtCl_4. Pt-Pb films were deposited at various potentials relative to the reversible potential for Pb/Pb2+ (E_(Pb/Pb2+) = -0.80 V SSE). A metastable fcc Pt-Pb solid solution is formed at potentials between -0.2 V SSE and -0.78 V SSE. A monotonic increase in the fcc lattice parameter with decreasing potential corresponds to a rise in Pb content that spans the composition range from Pt to beyond Pt3Pb. The intermetallics, PtPb, PtPb_(4) and elemental Pb form at more negative potentials. The films are single or multiphase depending on the growth potential and substrate. Thermal annealing leads to phase separation of the deposits into the respective equilibrium intermetallic phases whose volume fraction enables the overall film composition to be determined. At more negative potentials, between -0.79 V SSE and -0.82 V SSE, the ordered hexagonal PtPb intermetallic phase is directly formed by electrodeposition. Co-deposition of Pt_(100-x)Pb_(x) at potentials positive of -0.8 V SSE (EPb/Pb2+) occurs by a combination of Pb underpotential deposition with overpotential Pt deposition.