Structural Features of PLZT Films
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Structural Features of PLZT Films O. M. Zhigalinaa,b,*, D. N. Khmelenina, Yu. A. Valievac, V. Yu. Kolosovd, A. O. Bokuniaevad, G. B. Kuznetsove, K. A. Vorotilovf, and A. S. Sigovf a
Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” Russian Academy of Sciences, Moscow, 119333 Russia b Bauman State Technical University, Moscow, 107005 Russia c AO Transneft’ Neftyanye Nasosy, Chelyabinsk, 454010 Russia d Ural Federal University, Yekaterinburg, 620000 Russia e OOO Bruker, Moscow, 119017 Russia f Moscow Technological University (MIREA), Moscow, 119454 Russia *e-mail: [email protected] Received July 12, 2017
Abstract—Lead zirconate titanate (PZT) films doped with lanthanum, Pb(1 – х)Laх(Zr0.48Ti0.52) (х = 0, 0.02, 0.05, 0.08, or 0.01), have been investigated by electron microscopy and X-ray diffraction. Films were formed on Si–SiO2–TiO2–Pt substrates by chemical vapor deposition from a solution and annealed at temperatures T = 650 and 750°C. The main structural features of the films, differing them from undoped PZT films fabricated by the same method, have been established. It is found that doping with lanthanum delays the pyrochlore–perovskite transformation in the film bulk, i.e., in the regions distant from the film–substrate interface. The fraction of metastable pyrochlore phase increases with an increase in the La molar content in the films. The main reason for the delay is the deficit of lead in the intergranular perovskite space, especially in the upper part of the film. Annealing at T = 750°C reduces the content of pyrochlore phase but does not completely remove it, which was never observed for undoped PZT films. Doping with lanthanum leads to a change in the lattice period c and a tetragonal distortion of the perovskite lattice (c/a ratio). Hence, the [100] texture of the films obtained, in contrast to the typical [111] texture of PZT films, is due to the increase in the lattice mismatch between the film and platinum layer when lead atoms are replaced with lanthanum. Lattice distortions of “transrotational” character, whose value exceeds 160 deg/μm, are found to arise in growing crystals. DOI: 10.1134/S1063774518040314
INTRODUCTION Lead zirconate titanate (PZT) films are widely applied in microelectronics [1–6]. Memory cells of energy-independent devices based on PZT ferroelectric films contain capacitor elements, whose important characteristic is leakage currents. Doping PZT with elements like lanthanum is successfully applied to increase the resistance of bulky materials [4]. A study of the hysteresis loop of epitaxial and polycrystalline PZT films doped with lanthanum (PLZT), grown by different methods, showed that they remain typical ferroelectrics [7]. According to [8], the effect of doping with lanthanum manifests itself in a decrease in leakage currents by 1.5–2 orders of magnitude at electric field strengths higher than 100 kV/cm. Therefore, doping with lanthanum allows one to efficiently compensate for the majority carriers
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