Structural stability of layered n -LaFeO 3 -Bi 4 Ti 3 0 12 , BiFeO 3 -Bi 4 Ti 3 0 12 , and SrTiO 3 -Bi 4 Ti 3 0 12 thin

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hena) Department of Physics and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China

Shan-Tao Zhang and Yan-Feng Chen Department of Materials Science and Engineering and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China (Received 19 June 2012; accepted 5 September 2012)

A series of layered n-ABO3-doped Aurivillius structures Bi4Ti3O12 (BTO) thin films are synthesized on (001) SrTiO3 (STO) substrates by pulsed laser deposition, where n represents the number of ABO3 perovskite. X-ray diffraction substantiates that these films have expected layered Aurivillius structures. Furthermore, the microstructure of these samples is “systematically” characterized by transmission electron microscopy. It is found that the structure of n-STO-doped BTO becomes unstable when n is equal to 3, as revealed by the occurrence of intergrowth. Similar phenomenon is observed in n-LaFeO3-doped BTO; the layered Aurivillius structure is totally collapsed in the case of n as high as 2.5. In contrast, 3-BiFeO3-doped BTO still keeps perfect Aurivillius structure. The above-observed structural stabilities of these materials are explained by the theoretical formation enthalpy calculated by the density functional theory. This work provides the necessary information to explore the multifunctionality based on Aurivillius n-ABO3–BTO oxides. I. INTRODUCTION

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.337

On the one side, high density of intergrowth may shield the intrinsic physical property; on the other side, ordered intergrowth phases open a new avenue to tailor the physical properties.8 Among many structural characterization tools [such as x-ray diffraction (XRD), Raman spectroscopy], transmission electron microscopy (TEM) provides the direct and unambiguous study for the intergrowth in layered oxides.5,6 Up to now, there are a lot of TEM studies on layered perovskite oxides such as Srn 1 1RunO3n 1 1, Srn 1 1TinO3n 1 1, (La–A)n 1 1MnnO3n 1 1, and Bi2Sr2Can  1CunO7.5,6,9,10 Bi-contained oxide with “Aurivillius structure” is a member of layered perovskite oxides. Aurivillius structure, general formula as (Bi2O2)21(Am  1BmO3m 1 1)2, is formed by Bi2O2 layers interleaved with pseudoperovskite type layers Am  1BmO3m 1 1, where A, B, and O are two cations and oxygen anion in perovskite ABO3, respectively, m represents the number of BO6 oxygen octahedra between two successive Bi2O2 layers.11 Inserting the different Am  1BmO3m 1 1 (A 5 Sr, Ba, Pb; B 5 Fe, Ti, Cr, Mn) and various m leads to different physical properties, such as fatigue-free ferroelectricity in Bi4Ti3O12 (BTO),11 relaxor ferroelectric property in BaTiO3–BTO,12 as well as multiferroic property in Bi(Fe0.5Co0.5)O3–BTO.13 It is worth mentioning that there are two ways for inserting the pseudoperovskite layer ABO3 into the BTO.11 One is the integer insertion; the other is fraction number

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Ó Materials Research Society 2012

Layered perovskite oxides show th