  All the new layer perovskite superconductors seem to show a phenomenon of
symmetry mixing with repect to the order parameter. An analysis of the
different alternative of mixing and how far could them be presented is carried
out. For the particular case of s+id symmetry of the gap, the temperature
dependence of the specific heat ($C_{es}$) and the thermodynamic critical
magnetic field ($H_{c}$) are calculated. A double peak transition is observed
on $C_{es}(T)$ in the mixed regime while the single peak behavior is recovered
for a purely symmetric state (s or d). $C_{es}$ presents a quadratic law at low
tempeartures for a d-wave gap and for the s-wave one the typical exponential
attenuation. The temperature dependence of $H_{c}$ shows a clear phase
transition of second order at temperatures where the d-wave component becomes
negligible. A comparison with other results and experiments is done.

Condensed Matter