  The temperature and chemical potential dependent surface tension of bags is
introduced into the gas of quark-gluon bags model. The suggested model is
solved analytically. It resolves a long standing problem of a unified
description of the first and second order phase transition with the cross-over.
Such an approach is necessary to model the complicated properties of
quark-gluon plasma and hadronic matter from the first principles of statistical
mechanics. In addition to the deconfinement phase transition, we found that at
the curve of a zero surface tension coefficient there must exist the surface
induced phase tranition of the 2-nd or higher order, which separates the pure
quark gluon plasma (QGP) from the cross-over states. Thus, the present model
predicts that the critical endpoint of quantum chromodynamics is the
tricritical endpoint.
