Origin of abnormal structural transformation in a (BiPb)FeO3/SrRuO3/SrTiO3 hetero-structure probed by Rutherford backscattering

Murtaza Bohra,Kartikeya Negi,Hsiung Chou,Varun Karthik Y S,X Wang,W K Chu

doi:10.1038/s41598-017-04543-6

Abstract

Scientific efforts are growing to understand artificial BiFeO3/SrRuO3/SrTiO3-heterostructures, wherein an altered environment at each interface, caused by epitaxial strains, broken symmetry, off-stoichiometry and charge transfer, can generate a rich spectrum of exotic properties. Herein, (BiPb)FeO3/SrRuO3/SrTiO3-heterostructures were sputtered with various top (BiPb)FeO3-layers at different growth temperatures (Tg). Strain relaxation at each interface changes with Tg and generates an additional peak alongside with (BiPb)FeO3 at a high Tg of 700 °C. Rutherford backscattering (RBS) was employed to understand this unusual behavior as to whether it is a mixture of two phases, layer splitting or inter-diffusion of elements. Surprisingly, complete overlapping of random and aligned RBS spectra from the sample with Tg = 700 °C indicates the presence of a large amount of defects/distortions at the interfaces. The RBS compositional analysis gives clear evidence of Fe and Ru vacancies to an extent that the structural integrity may not be maintained. This abnormal condition can be explained by the inter-diffusion of Pb and Bi elements into whole films and even into the top layer of the SrTiO3 substrate, which compensates for these vacancies by substitutional replacement and is responsible for the generation of the additional SrTi(BiPb)O3—peak. Below TcSrRuO3, the magnetic properties change significantly with Tg.

Highlights

(BiPb)FeO3/SrRuO3/SrTiO3-heterostructures were sputtered with various top (BiPb)FeO3-layers at different growth temperatures (Tg)
In another study[11], we have shown an inverse effect in (BiPb)FeO3/SrRuO3/SrTiO3 heterostructures, with an increase in thickness of the top (BiPb)FeO3layers (50–400 nm), and an anomalous decrease in unit cell volume of the bottom SrRuO3 layer
Commonly the best BiFeO3 films were obtained in the growth temperature range 600–700 °C either by PLD or sputtering[14,15,16], and it’s imperative to study these films at elemental level in order to get in depth knowledge of interfacial mixing or inter-diffusion of elements otherwise their stoichiometry will be remained doubtful

Summary

Introduction

(BiPb)FeO3/SrRuO3/SrTiO3-heterostructures were sputtered with various top (BiPb)FeO3-layers at different growth temperatures (Tg). The RBS compositional analysis gives clear evidence of Fe and Ru vacancies to an extent that the structural integrity may not be maintained This abnormal condition can be explained by the inter-diffusion of Pb and Bi elements into whole films and even into the top layer of the SrTiO3 substrate, which compensates for these vacancies by substitutional replacement and is responsible for the generation of the additional SrTi(BiPb)O3—peak. In the recent study[9], we used reciprocal space mappings (RSMs) to demonstrate structural expansion (from cubic to tetragonal, and a mixture of two tetragonal phases) and suppression of spiral spin state in Pb doped BiFeO3 ((BiPb)FeO3) layers with varying growth temperature (650–700 °C). We highlight new interface phenomena in (BiPb)FeO3/ SrRuO3/SrTiO3 heterostructures grown at critical growth temperature range 650–700 °C by using Rutherford backscattering as a probe to identify the phases of each layers. We further propose a mechanism for the observed secondary phase that provides insight into the competing nature of the phases in this system

Methods

Results

Conclusion