We discuss the nature of the pairing mechanism and the physical properties
associated with the normal as well as the superconducting state of cubic pe
rovskites Ba0.6K0.4BiO3 using the strong coupling theory. An interaction po
tential which includes the Coulomb, electron-optical phonon and electron-pl
asmon interactions is developed to elucidate the superconducting state. A m
odel dielectric function is constructed with these interactions fulfilling
the f-sum rule. The screening parameter (mu* = 0.26) infers the poor screen
ing of charge carriers. The electron-optical phonon strength (lambda) estim
ated as 0.98 is consistent with an attractive electron-electron interaction
and supports the moderate to strong coupling theory. The superconducting t
ransition temperature of Ba0.6K0.4BiO3 is then estimated as 32 K. Ziman's f
ormula of resistivity is employed to analyse and compare this with the temp
erature-dependent resistivity of a single crystal. The estimated contributi
on from the electron-optical phonon together with the residual resistivity
clearly infers a difference when a comparison is made with experimental dat
a. The subtracted data infer a quadratic temperature dependence in the temp
erature domain (30 less than or equal to T less than or equal to 200 K). Th
e quadratic temperature dependence of rho [= rho(exp) - (rho(0) + rho(e-ph)
)] is understood in terms of 3D electron-electron inelastic scattering. The
presence of these el-el and el-ph interactions allows a coherent interpret
ation of the physical properties. Analysis reveals that a moderate to stron
g coupling exists in the Ba0.6K0.4BiO3 system and the coupling of electrons
with the high-energy optical phonons of the oxygen breathing mode will be
a reason for superconductivity. The implications of the above analysis are
discussed. (C) 1998 Academic Press.