Crystalline and Electrical Properties of Ferroelectric Silver Niobate-tantalate thin Films
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Crystalline and electrical properties of ferroelectric silver niobate-tantalate thin films Jung-Hyuk Koh a, S.I. Khartsev a, Alex Grishin a, Vladimir Petrovsky b a Condensed Matter Physics, Department of Physics, Royal Institute of Technology, Stockholm, S-100 44, Sweden; b Department of Ceramic Engineering, University Missouri-Rolla, EMARC, Rolla, MO.
ABSTRACT For the first time AgTa0.38Nb0.62O3 (ATN) films have been grown on the La0.7Sr0.3CoO3 (LSCO)/LaAlO3 single crystal as well as onto Pt80Ir20 (PtIr) polycrystalline substrate. Comprehensive X-ray diffraction analyses reveal epitaxial quality of ATN and LSCO films on the LaAlO3(001) substrate, while ATN/PtIr films have been found to be (001) preferentially oriented. Dielectric spectroscopy performed for ATN films and bulk ceramics in a wide temperature range 77 to 420 K shows the structural monoclinic M1-to-monoclinic M2 phase transition occurs in films at the temperature 60 °C lower than in ceramics. The tracing of the ferroelectric hysteresis P-E loops indicates the ferroelectric state in ATN films at temperatures below 125 K and yields remnant polarization of 0.4 µC/cm2 @ 77 K. Weak frequency dispersion, high temperature stability of dielectric properties as well as low processing temperature of 550 °C make ATN films to be attractive for various applications.
INTRODUCTION The great potential of high dielectric permittivity and low loss ferroelectrics as frequency agile materials, has recently attracted great attention. Such materials, when incorporated into devices, need to operate over wide bandwidths, handle high microwave power without breakdown, possess wide electrical tuning, and minimal loss. Perovskite (Ba,Sr)TiO3 (BST) [1], SrTiO3 (STO) [2], and BaTiO3 (BTO) [3] films are considered to be the candidates for electrically tunable microwave components. A recent microwave-submillimeter-to-infrared spectroscopic study [4] has proved silver niobate-tantalate solid solutions AgTaxNb1-xO3 (ATN) should also be regarded to the family of microwave ceramics. A.Kania [5] has reported perovskite silver niobate-tantalate solid solutions show high dielectric permittivity and low loss tan δ in bulk ceramics, but to the best of our knowledge ATN has not been yet investigated in thin film form. One possible reason is the high volatility of the Ag component, which complicates ferroelectric thin film fabrication. In this paper, we report on highly crystalline ATN films deposited on LSCO/LaAlO3 single crystal and onto Pt80Ir20 (PtIr) polycrystalline substrates, as well as results of comparative analyses of ATN bulk ceramics and thin film dielectric and ferroelectric properties. Fabricated ATN films exhibit high temperature stability and weak frequency dispersion of dielectric properties, dielectric permittivity about 500 and loss tan δ ~ 0.008 at 100 kHz, electrical tunability 1-ε(56 kV/cm)/ε(0) ~ 32%@77 K, and remnant polarization Pr (77 K) ~ 0.4 µC/cm2.
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EXPERIMENTAL PROCEDURES
220 Pt-220
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Intensity(a.u.)
XRD data for the ATN films deposited onto
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