Properties of Pb(Zr,Ti)O$_3$ ultrathin films under stress-free and open-circuit electrical boundary conditions

TL;DR

This study uses first-principles simulations to explore the properties of ultrathin Pb(Zr,Ti)O$_3$ films, revealing persistent polarization, polarization rotation, and altered phase transition behavior under stress-free and open-circuit conditions.

Contribution

It introduces a first-principles-based scheme to analyze ultrathin ferroelectric films under specific boundary conditions, highlighting polarization behavior and phase transition changes.

Findings

Polarization persists down to minimal thickness.

Polarization rotates between <010> and <110> directions near x=0.50.

Phase transition order changes from bulk to thin films.

Abstract

A first-principles-based scheme is developed to simulate properties of (001) PbO-terminated Pb(Zr$_{1-x}$Ti$_{x}$)O$_3$ thin films that are under stress-free and open-circuit boundary conditions. Their low-temperature spontaneous polarization never vanishes down to the minimal thickness, and continuously rotates between the in-plane <010> and <110> directions when varying the Ti composition around x=0.50. Such rotation dramatically enhances piezoelectricity and dielectricity. Furthermore, the order of some phase transitions changes when going from bulk to thin films.