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ABSTRACT The effect of growth conditions such as substrate temperature and oxygen partial pressure on the microstructure and properties of pulsed laser deposited SBTN thin films on Si(100) and MgO(100) substrates have been studied. Crystallization of films begins at room temperature but, the obtained phase was non-ferroelectric. The influence of oxygen pressure (150 to 450 mTorr) on crystallinity of the films deposited on Si(100) at 750'C is negligible. XPS studies of as-deposited films reveal that the oxygen vacancies are preferably present near the Bi ions at the Bi 2 0 2 layers and vary with substrate temperature and oxygen partial pressure. Also, XPS studies of Sr 3d core level for SBTN films suggest that the oxygen ions in the Sr(Ta/Nb) 2 0 7 perovskite layers are much more stable than those in the Bi 2 0 2 layers. Micro-Raman studies of SBTN films deposited below 7000C show Raman modes of a non -ferroelectric phase. INTRODUCTION It has been well established that bismuth based ferroelectric compounds, such as SrBi 2 Ta2 0 9 (SBT), SrBi2 Nb 2O 9 (SBN), and SrBi2 Ta 0 .8Nb1 .209 (SBTN), have a significant advantage over Pb based ferroelectric materials which usually show fatal fatigue failures with Pt electrodes[ 1]. In the Bi-layer structurd family, a large number of compounds of the general form (Bi 2 02)2+ (An-,BnO 3,+]) 2 -, where A = Ba, Pb, Sr, Bi, K or Na, n = 2, 4 or 5 and B = Ti, Nb or Ta, are known to be ferroelectric [2-4]. The presence of perovskite like layers consisting of B0 6 octahedra lead to spontaneous polarization in the plane of these layers. No polarization along the c-axis [5-8], where the continuity of the perovskite like layers is interrupted by the presence of Bi 2 0 2 layers also take part in the cooperative phenomenon that is responsible for ferroelectricity in these materials. Any doping at the octahedral site can have considerable effect on Bi 2 0 2 layers [4,8]. SBT thin films have been successfully grown by sol-gel, pulsed laser deposition, metalorganic chemical vapor deposition and sputtering methods [9-12]. SrBi 2Nb2 O 9 (SBN) has larger remanent polarization and coercive field than SBT [13]. Desu and Vijay have identified that SrBi 2 Tao. 8Nbl. 20 9 (SBTN) ferroelectric films are promising candidates for NVRAM applications as a result of their fatigue free nature [8,9]. Several studies have been reported on the mechanical, electrical and thermal properties of most of these Bi

191 Mat. Res. Soc. Symp. Proc. Vol. 596 ©2000 Materials Research Society

based layered thin films. Studies of the lattice vibrational properties will help to understand the structural properties associated with the ferroelectric phase transition and the polarization state. Unfortunately only a few reports exist on micro-Raman studies of these thin films [14,15]. In single crystal form, Graves et al. have correlated the trends in the Raman spectra with the chemical and structural relationships among the Aurivillius phases, and have compared the results with other layered oxides containing perovskite like