  A new experimental set-up controlled by computer has been made to measure the
pyroelectric charge of ferroelectric materials with a relatively high
conductivity at slow rates of temperature variation. It allowed us to obtain
the polarisation vs. temperature behaviour of PZT with various compositions in
the whole range of temperatures with a high accuracy. The ferroelectric Zr-rich
region of the PZT phase diagram, where the isostructural phase transition
FRL-FRH takes place, has been studied.
