Tip Induced Surface Defect migration and Conductivity Studies in Tetragonal, Rhombohedral and Mixed-Phase epitaxial BiFe
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.463
Tip Induced Surface Defect migration and Conductivity Studies in Tetragonal, Rhombohedral and Mixed-Phase epitaxial BiFeO3 Thin Films Saj Mohan M M1,*, Sreenath M V1, Ranjith Ramadurai1 1
Department of Materials Science and Metallurgical Engineering, IIT Hyderabad, Sangareddy, Kandi, Telangana, India-502285.
ABSTRACT
BiFeO3 (BFO) is the most studied room temperature multiferroic compound. In this work we demonstrate a template assisted growth process through which the growth strain is controlled to achieve required phase of BFO. Growth of (~20nm) fully strained tetragonal (T), rhombohedral (R) and mixed phase of T and R of Bismuth ferrite (BiFeO 3) was achieved by varying the thickness of the template layer. The different phases were confirmed by using high resolution x-ray diffractions studies. The conductivity map of all the three phases were carried out using an atomic force microscope operating in conductive mode. Tip induced surface defect migration within a given grain was observed in pure phases and the conductivity map confirmed the same. The room temperature resistivity is found to be decreasing systematically from 1.1×106 Ωm , 935×105 Ωm and 1.16×104 Ωm respectively for tetragonal, mixed phase and rhombohedral phase BFO. In the case of mixed phase both the nano- scale and macroscopic leakage current studies show low conductivity, which could be due to the increased pinning sites that increases the energy barrier for the defect migration. The local nano-scale measurements and conductivity mapping corroborates well with the macroscopic studies.
INTRODUCTION Bismuth ferrite (BFO) is the most studied room temperature multiferroic for the interesting properties it possess and the rich science it offers on the fundamental understanding of multiferroics. BFO has a ferroelectric (FE) Curie temperature of 1100 K and antiferromagnetic Neel temperature of ~643 K[1-2]. At room temperature BFO stabilizes in a rhombohedral structure (R3c) structure that allows the ferroelectric displacement of Fe cation in the pseudocubic [111] direction. There have been few studies on substrate induced compressive strain that stabilizes a tetragonal like BFO in epitaxial thin films[3-4]. In case of the tetragonal structure the polarization direction is in the pseudocubic [001] axis. However, in case of rhombohedral BFO grown as possess a polarization along [111] axis. However, the structural tunability was achieved by altering the substrates and the template layers utilized on the substrates. It is also known that the FE domain pattern of BFO epilayers are sensitive to the bottom layer on which it is
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grown.[5] In addition there are reports detailing the conductive nature of the domain walls in BFO. In this study we a
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