  The analysis of the structure, chemical stability, electronic and
ferroelectric properties of the interfaces between Pt(001) and PbZrTiO$_3$(001)
(PZT) have been performed with $ab$ $initio$ methods. We show that the chemical
environment plays a critical role in determining the interfacial reconstruction
and charge redistribution at the metal/oxide interfaces. We demonstrate that
the difference in interfacial bonds formed at the Pt/PZT interfaces with
(TiZr)O$_2$ - and PbO- termination of PZT essentially defines the effectiveness
of the screening, and ease of polarisation switching in PZT-based capacitors.
The imperfect screening in Pt/PZT/Pt capacitors is caused by strong interfacial
bonds formed at the interface with (TiZr)O$_2$-terminated film, which is
accompanied by the suppressed polarisation of PZT film. In contrast, the
capacitors with PbO-terminated PZT show a negligible depolarising field and
high polarisation, which is the consequence of weak bonds formed at this type
of interfaces. The latter also causes a higher switching barrier than that in
the former system.
