Coexistence of polar distortion and metallicity in PbTi1-xNbxO3

TL;DR

This study demonstrates the coexistence of metallicity and polar distortion in PbTi1-xNbxO3 through doping, challenging the traditional view that ferroelectricity cannot coexist with metallic behavior, and suggests potential for designing new functional materials.

Contribution

It provides experimental and theoretical evidence of ferroelectric-like polar distortion coexisting with metallicity in doped PbTi1-xNbxO3, a new candidate for ferroelectric metals.

Findings

Polar distortion persists with doping up to x=0.12.

PbTi1-xNbxO3 becomes metallic at x=0.12.

Nb doping introduces free electrons without destroying dipoles.

Abstract

Ferroelectricity has been believed unable to coexist with metallicity since the free carriers can screen the internal coulomb interactions of dipoles. Very recently, one kind of materials called as ferroelectric metal was reexamined. Here, we report the coexistence of metallicity and polar distortion in a new candidate for ferroelectric metal PbTi1-xNbxO3 via doping engineering. The ferroelectric-like polar distortion in all the doped PbTi1-xNbxO3, with x ranging from 0.04 to 0.12, was confirmed by the piezoresponse force microscopy and the scanning transmission electron microscopy measurements. PbTi1-xNbxO3 films become more conductive with more doping density, and emerge a metallic behavior when x reaches 0.12. Our first principle calculations further revealed that the doped Nb ions in the films can only provide free electrons, but not be able to damage the dipoles in unite cells even with the heaviest doping density of 0.12 due to their little impact on the off-centering of the Ti ions. We believe that these results confirm a feasibility of realizing the coexistence of metallicity and polar distortion for other ferroelectrics in a common way, and motivate the synthesis of some new materials with artificially designed properties even incompatible in nature.