Mn-Doped BaTiO₃Thin Film Sintered Using Nanocrystals and Its Dielectric Properties

Abstract

BaTiO 3 thin films homogeneously doped with Mn were prepared by a novel powder-sintering thin-film process. Mn-doped BaTiO 3 nanocrystals 5 -7 nm in diameter were synthesized by a sol-gel method and sintered to form a highly densified microstructure containing columnar grains epitaxially grown on a (111)-oriented Pt/TiO 2 /Al 2 O 3 substrate at a low temperature of 800 C. On the basis of the results of various structural analyses, Mn was suggested to act as an acceptor in the perovskite structure of BaTiO 3 , which was also supported by the experimental finding indicating that the leakage current density was significantly improved compared with that of a nondoped BaTiO 3 thin film. Moreover, the dielectric constant of the Mn-doped BaTiO 3 thin film, 728 at 10 kHz with a loss tangent of 1.3%, was higher than that of the nondoped BaTiO 3 thin film, probably owing to the electrostrictive effect induced by in-plane tensile stress. These results clearly indicate the feasibility of using doped BaTiO 3 nanocrystals in the powder-sintering thin-film process for improving dielectric properties.

The coexistence of ferroelectricity and ferromagnetism in Mn-doped BaTiO3thin films

“…The Mn ions in BaTiO 3 have a fluctuating valence state between +2 and +4, which can compensate for the oxygen vacancies to keep the sample electrically neutral. [28] Mn dopant ions act as acceptors in the BaTiO 3 thin films and thus form positively charged trapping centres in the band gap. The trapping process can be described as follows:…”

Decisive role of oxygen vacancy in ferroelectric versus ferromagnetic Mn-doped BaTiO3 thin films

“…At low frequency, those trapping centers cause the increase of tanδ. 24 The ε r of the BTMO-100 and BTO-100 thin films is rather constant over the entire investigated frequency range. The ε r of the BTMO-100 thin films is smaller than that of the BTO-100 thin films, indicating that an excessively high concentration of Mn-doping decreases the ε r of BTMO thin films.…”

“…The Mn ions in BaTiO 3 have a fluctuating valence state between +2 and +4, which can compensate the oxygen vacancies to keep the sample electrical neutral. 24 Mn ions act as acceptors in the Mn-doped BaTiO 3 thin films and thus form positively charged trapping centers in the band gap. The trapping process can be described as follows: 25 Mn Ti × + e ' ↔ Mn Ti '…”

“…The higher tanδ of the BTMO-100 thin film can be accounted for by the existence of trapping centers in the band gap as compared to the BTO-100 thin film, which agrees with the presence of three different regions in the I-V curve. At low frequency, those trapping centers cause the increase of tanδ 24.…”

Effects of Manganese Doping on the Dielectric Properties of Titanium Dioxide Ceramics

“…These requirements were met through optimization of processing parameters and incorporation of appropriate dopants at optimum concentrations. It has been well established that Mn doping is effective in achieving of high insulation resistance in BaTiO 3 ‐based dielectrics, 16,17 In Mn‐doped BaTiO 3 , oxygen vacancies ( V O •• ) and ionized acceptors (Mn′ Ti and/or Mn″ Ti ) are the dominant defects, which prevent the reduction of BaTiO 3 (in reduced BaTiO 3 oxygen vacancies and electrons are the dominant defects). In addition, it was reported that dielectric loss (at 3 GHz) of TiO 2 ceramics was greatly reduced by introducing divalent or trivalent dopants with ionic radius in the range of 0.50–0.95 Å (ionic radius of Mn 2+ : 0.80 Å), as the reduction of Ti 4+ was prevented 18 .…”