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U6.6.1

Dielectric Properties of Pulsed Excimer Laser Ablated BaBi2Nb2O9 Thin Films Apurba Laha and S.B.Krupanidhi Materials Research Center, Indian Institute of Science, Bangalore 560 012, INDIA S. Saha Materials Science Divisions, Argonne National Laboratory, 9700, S. Cass Avenue, Argonne, IL-60439, USA ABSTRACT The dielectric response of BaBi2Nb2O9 (BBN) thin films has been studied as a function of frequency over a wide range of temperatures. Both dielectric constant and loss tangent of BBN thin films showed a ‘power law’ dependence with frequency, which was analyzed using the Jonscher's 'universal dielectric response model. Theoretical fits were utilized to compare the experimental results and also to estimate the value of temperature dependence parameters such as n(T) and a(T) used in the Jonscher's model. The room temperature dielectric constant (ε′) of the BBN thin films was 214 with a loss tangent (tanδ) of 0.04 at a frequency of 100 kHz. The films exhibited the second order dielectric phase transition from ferroelectric to paraelectric state at a temperature of 220 oC. The nature of phase transition was confirmed from the temperature dependence of dielectric constant and sponteneous polarization,respectively. The calculated Currie constant for BBN thin films was 4x 105 oC.

INTRODUCTION In the recent years, ferroelectric materials particularly Bi-layered structure compounds have attracted great attention of the people for their advantageous application in the new generation data storage devices such as nonvolatile random access memories (NVRAMs),[1,2] smart cards [3]etc. The Bi- layered structure compounds such as SrBi2Ti2O9 (SBT)[4], SrBi2Nb2O9 (SBN),[5] their solid solution (SBTN),[6] BaBi2Ta2O9 (BBT) [7], and BaBi2Nb2O9 (BBN) [8] have unique properties such as higher remanent polarization, better fatigue endurance, low coercive field which made them as the most promising candidate for non volatile memory devices in CMOS industry. Although PZT thin film has great potential in NVRAMs application because of its higher remanent polarization, the major drawback of this material is the polarization degradation, which is one of the serious issues of NVRAMs devices.[9] In that respect Bi- layered compounds like SBT and SBN have been found to be the most suitable substitutes in the new generation data storage devices without any significance loss of polarization up to 1010 to 1012 cycles.[10] These layered structure compounds belong to the Aurivillius family with a pseudo tetragonal perovskite crystal structure intervened by (Bi2O2)+2 layers.[11] Although there is considerable interest in the thin films of SBT, SBN and their solid solution for use in ferroelectric memories, little interest has been paid on the thin films of BBN, which is also a member of same family. The crystal structure of BBN is similar to

U6.6.2

SBTN group. We have already reported the successful growth of polycrystalline BBN thin films [8] at lower temperature with subsequence ex-situ annealing using pulsed laser ablation technique. The r