Role of stress on the phase control and dielectric properties of (1-x) BiFeO 3 - xBa 0.5 Sr 0.5 TiO 3 solid solution thi

  • PDF / 181,177 Bytes
  • 6 Pages / 612 x 792 pts (letter) Page_size
  • 2 Downloads / 184 Views

DOWNLOAD

REPORT


O12.10.1

Role of stress on the phase control and dielectric properties of (1-x) BiFeO3 - x Ba0.5Sr0.5TiO3 solid solution thin films Chin Moo Cho, Hee Bum Hong, and Kug Sun Hong School of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea ABSTRACT Dielectric properties and structure of (1-x) BiFeO3 (BFO) - x Ba0.5Sr0.5TiO3 (BST) (x = 0 ~ 1) solid solution thin films were investigated. All films were prepared at 600 oC on (111) oriented Pt / TiO2 / SiO2 / Si substrates by pulsed laser deposition (PLD) technique. Solid solution could be achieved in all composition ranges, evidenced by X-ray diffraction (XRD) and field emission scanning electric microscope (FE-SEM). The intermediate compositions (0.4 ≤ x ≤ 0.8) exhibited a distinct (111) oriented cubic perovskite structure, while rhombohedra symmetry was found in the x < 0.4 range. Dielectric constant and tunability of the (1-x) BFO – x BST films within this composition region (0.4 ≤ x ≤ 0.8) decreased from 1110 to 920 at 1 MHz, and increased from 28.34 % to 32.42 % at 200 kV/cm, respectively, while loss tangent remains constant. A systematic decrease in lattice parameter with BST addition reduced stress due to reduction of lattice parameter mismatch between film and the substrate. In that range, the improvement of the dielectric properties without a degradation of loss tangent is attributed to the presence of the stress relaxation, which was quantitatively confirmed by a surface profiler based on Stoney’s equation. INTRODUCTION Recently, perovskite structure such as BiFeO3 (BFO) [1] has attracted much attention as it shows coexistence of ferromagnetic (antiferromagnetic) and ferroelectric ordering simultaneously. These materials present opportunities for potential applications in information storage, the emerging field of spintronics and sensors [2, 3]. It has been reported that BFO has rhombohedrally distorted simple perovskite structure showing ferroelectric properties with high Curie temperature (Tc ~ 850℃) and antiferromagnetic behavior with Néel temperature (Tn ~ 370 ) simultaneously [4, 5]. BFO is interested in terms of practical applications, because both electrical and magnetic ordering temperatures of BFO are well above room temperature. Unfortunately, application of the BFO has been interrupted by leakage problems, likely a result of defects and nonstoichiometry. To overcome this obstacle, recent work has focused on solid solutions of BFO with ABO3 materials, such as BaTiO3 and Pb(Zr, Ti)O3.

O12.10.2

In this study, solid solution was formed by mixing a certain amount of BFO and Ba0.5Sr0.5TiO3 (BST), perovskite structure material. The (1-x) BFO – x BST solid solution targets were made at the range of 0.4 ≤ x ≤ 0.8, and then the thin films were deposited on (111) preferred Pt / TiO2 / SiO2 / Si substrates by pulsed laser deposition (PLD) technique. The thin films having orientations were studied in the view of stress and the characteristics changes of lattice mismatch between the substrate and thin film. The relation of stres

Data Loading...