Nanoscale Piezoelectric Properties and Phase Separation in Pure and La-Doped BiFeO3 Films Prepared by Sol-Gel Method.

Alina V Semchenko,Oleg Pakhomov,Sergei A Khakhomov,Vladimir E Gaishun,Igor Bdikin,Vitaly V Sidsky,Andrei L Kholkin,Svitlana Kopyl,Dmitry L Kovalenko

doi:10.3390/ma14071694

Alina V Semchenko, Oleg Pakhomov + Show 7 more

Open Access

https://doi.org/10.3390/ma14071694

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Abstract

Pure BiFeO3 (BFO) and doped Bi0.9La0.1FeO3 (BLFO) thin films were prepared on Pt/TiO2/SiO2/Si substrates by a modified sol–gel technique using a separate hydrolysis procedure. The effects of final crystallization temperature and La doping on the phase structure, film morphology, and nanoscale piezoelectric properties were investigated. La doping and higher crystallization temperature lead to an increase in the grain size and preferred (102) texture of the films. Simultaneously, a decrease in the average effective piezoelectric coefficient (about 2 times in La-doped films) and an increase in the area of surface non-polar phase (up to 60%) are observed. Phase separation on the films’ surface is attributed to either a second phase or to a non-polar perovskite phase at the surface. As compared with undoped BFO, La-doping leads to an increase in the average grain size and self-polarization that is important for future piezoelectric applications. It is shown that piezoelectric activity is directly related to the films’ microstructructure, thus emphasizing the role of annealing conditions and La-doping that is frequently used to decrease the leakage current in BFO-based materials.

Highlights

There has been a rising interest in multiferroic materials, which demonstrate both magnetic and polarization order and resulting coupling between them in a single phase [1,2,3,4,5,6,7]
One of the disadvantages of BiFeO3 films is due to their high conductivity explained by different oxidation states of Fe ions, Fe3+ and Fe2+, which result in the appearance of oxygen vacancies that are responsible for the hopping conduction [8,9]
Pure BiFeO3 and Bi0.9La0.1FeO3 thin films were prepared on Pt/TiO2/SiO2/Si substrates by a modified sol–gel technique using a separate hydrolysis procedure

Summary

Introduction

There has been a rising interest in multiferroic materials, which demonstrate both magnetic and polarization order and resulting coupling between them in a single phase [1,2,3,4,5,6,7]. Doping of BFO has been extensively studied in the past: there were reports on Tb [10], La [11,12], Ce [13], Eu, Gd, Dy [14] doping for A-site and Ti [8], Cr [15], Zr [16], Mn [17] substitutions at B-site Using these substitutions it was possible to stabilize the valence of iron with the simultaneous decrease of conductivity. La-doping was frequently used to create structurally metastable states with both enhanced piezoelectricity and reduced leakage [8,9] These states, characterized by notable magnetic properties, may occur at the boundaries of nanosized grains and various interfaces in thin films. No detailed nanoscale measurements of piezoelectric activity in doped BiFeO3 films have not been reported yet

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