Structural and Electrical Investigations of Ferroelectric Lead Strontium Titanate Thin Films and Ceramics
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Structural and Electrical Investigations of Ferroelectric Lead Strontium Titanate Thin Films and Ceramics M. Jain1, P. Bhattacharya1, Yu.I. Yuzyuk2, R.S. Katiyar2, and A.S. Bhalla3 1 Department of Physics, University of Puerto Rico, San Juan, PR 00931 2 Faculty of Physics, Rostov State University, Zorge 5, Rostov-on-Don, 344090, Russia 3 Materials Research Institute, The Pennsylvania State University, University Park, PA-16802, USA
ABSTRACT Lead strontium titanate (PbxSr1-xTiO3) (x=0.3-1.0) ceramic targets were prepared by the conventional powder-processing method. Thin films of these compositions were deposited on platinized silicon substrates by pulsed laser deposition technique. X-ray diffraction studies of the ceramic targets showed that the lattice structure changes from tetragonal to cubic phase with the increase of Sr content in PbTiO3. Raman spectroscopic studies of PbxSr1-xTiO3 (PST) ceramics and thin films showed that the soft mode decreases to lower frequency and finally disappear at around 60-70 at% Sr content, which confirms the tetragonal to cubic phase transition at room temperature. Dielectric constant measured for PST thin films was in the range of 900-1500 at 1 MHz, with maximum value obtained for PST30 thin film. The loss tangents at room temperature were in the range of 0.07-0.1 for PST thin films with different compositions.
INTRODUCTION Lead titanate (PbTiO3) belongs to perovskite structure with a simple ferroelectric to paraelectric cubic transition around 490oC. On the other hand, strontium titanate (SrTiO3) is a quantum paraelectric [1] whose dielectric constant continues to increased upon cooling down to about 4K, below which it levels off due to zero-point quantum fluctuations. It is reported that PbTiO3 (PT) forms continuous range of solid solution with SrTiO3 (ST) and the lattice volume and tetragonality of PT increase with the increasing Sr2+ content. The Curie temperature of PbxSr1-xTiO3 (PST) was found to decrease as the Sr content increases in solid solution [2]. PST is considered as one of the potential candidate materials for the future tunable microwave device components such as resonators, filters etc. when used in paraelectric region and also for ultralarge-scale integration (ULSI) dynamic random access memory (DRAM) capacitors in the ferroelectric region. The main peculiarity is that for compositions of PST with x ≤ 0.3 the Curie temperature is below the room temperature. Also the dielectric loss in some of the PST compositions is relatively smaller as compared to the BST compositions. The studies are therefore desirable to understand the intrinsic behavior of the loss mechanism and its relation to the soft modes in such systems. The close relationship between the ferroelectricity and the lattice dynamics makes Raman spectroscopy a valuable technique for the study of ferroelectric materials. In some ferroelectrics
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the low frequency soft mode was found to soften near ferroelctric-paraelectric phase transition. In case of bulk materials, the phase transiti
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