Preparation of Na 0.5 K 0.5 NbO 3 /La 0.6 Sr 0.2 Mn 1.2 O 3 /LaAlO 3 Thin Film Structures by Pulsed Laser Deposition
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ABSTRACT We report on ferroelectric/giant magnetoresistive Na0 .5K0 .5Nb0 3/La0.6Sro. 2Mnj203 (NKN/LSMO) heterostructures grown onto LaAIO 3 (001) single crystal using KrF pulsed laser ablation of stoichiometric ceramic target. Main processing parameters have been optimized to obtain smooth LSMO template layer, avoid NKN-LSMO interdiffusion, preserve NKN stoichiometry against the lost of volatile potassium and sodium and achieve reasonable reliability of NKN film performance. X-ray diffraction 0- 20 scans and rocking curves evidence for single-phase content and high c-axis orientation both in template LSMO and top NKN layers. Ferroelectric measurements yield remnant polarization Pr of 1.5 2 [LC/cm2 and spontaneous polarization P, of 7 pC/cm at electric field strength of 130 kV/cm. At room temperature, dielectric permittivity c' and dissipation factor tane5 have been found to vary from 595 to 555 and 0.046 to 0.029 respectively in the frequency range of 0.4 to 20 kHz. At 10 kHz dielectric permittivity linearly increases from 410 to 650 in the temperature range 77 K to 415 K while the dissipation factor below 320 K does not exceed 3%. INTRODUCTION Perovskite sodium-potassium niobate system was studied extensively in bulk ceramic form long ago because it showed a number of ferroelectric phases with high spontaneous polarization and piezoelectric activity [1-3]. The system has revealed the presence of phase boundaries at approximately 52.5, 67.5, 82.5, and 98.2 mole % of NaNbO 3 at room temperature in addition to one very near the NaNbO 3 end member. NaxKl_.NbO 3 (x < 0.525) has essentially same structure that of pure KNbO 3 (point group mm2: a = c # b, ca =3 = 90' # y). When x is increased (0.525 < x < 0.675), it transforms to different phase (point group pm: a # c > b, cc = P3= 90' # y). At x = 0.5, in the vicinity of this boundary, maximum radial coupling coefficient was observed and exhibited wide temperature range, from -130 'C to 200 'C, in which there are no phase transformations [1,2]. Recently, the perovskite sodiumpotassium niobate thin films attract revived attention. Strong electric field dependence of rather low dielectric permittivity with very low loss, and high piezoelectric coefficient promise vast variety of applications in a wide operating temperature range [4]. However, fabrication of NKN in thin film form is rather complicated, because of its high volatile constituents namely sodium and potassium. Several groups reported sodium and potassium losses in Na- and K-based films grown by PLD and sputtering techniques [5,6]. Moreover, the vacancies of monovalent Na and K ions are the main reason of ionic conductivity, which
restrict the performance of ferroelectric NKN films. Very recently we have demonstrated 249 Mat. Res. Soc. Symp. Proc. Vol. 574 © 1999 Materials Research Society
highly c-axis oriented single phase NKN thin films on polycrystalline PtNoIr 20 substrate made by laser ablation of stoichiometric ceramic target [7]. In this article, we report on the PLD growth of NKN on LSMO underlayer o
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