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Barrier Layer Concepts in Doped BaTiO3 Ceramics

Tennakone, Harshani
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367937169

Abstract Details

2013, PhD, University of Cincinnati, Engineering and Applied Science: Materials Science.
Barium titanate is one of the most extensively studied dielectric and ferroelectric ceramic, continuing to be the material of choice for many applications. Its use as a dielectric for capacitors, thermisters, piezoelectric transducers and memory devices are well known. This research reveals that exceptionally high dielectric constants and other attributes desired for electronic and energy storage device applications are achievable by selected isovalent and aliovalent doping of barium titanate. Doping of barium titanate with Nd3+ and co-doping with Zr4+ is being studied to elucidate the complex interactions involved in the formation of grain boundary and surface barrier layers and other morphological characteristics. Observed dielectric relaxations of the system are related to charge compensation mechanisms and dielectric properties in terms of equivalent circuits, brick layer and Maxwell Wagner-Debye models. The perovskite structure of barium titanate admits either isovalent or aliovalent substitutions depending on dopant ionic radii. Isovalent substitutions generally modify the morphology of the ceramics and induce phase changes. Aliovalent substitutions, notably trivalent rare earth ions such as Nd, modulate electronic properties inducing semiconductivity at lower concentrations. At higher concentrations or under oxidizing conditions, ionic compensation retains insulation. The most remarkable feature observed in this study is the oxygen partial pressure driven solubility of Nd in barium titanate at intermediate dopant concentrations, generating surface barrier layer morphologies with gradient variations in Ti3+ from surface to the interior, exhibiting complex relaxation mechanisms. The study confirmed that macroscopic barrier layers over the sample surface and microscopic barrier layers in the grain boundaries profoundly influence dielectric properties, offering avenues for developing materials of high dielectric constant, low loss and good stability. Nd2O3 doping from 0.3 to 0.5 mol% was identified as the region where a diffused surface barrier layer and grain boundary barrier layers coexist. Variation of charge composition and processing parameters within this range enabled producing a material of room temperature dielectric constant exceeding 20000 and a loss ~ 0.1. Aliovalent co-doping with ZrO2 yielded a structure with semiconducting cores and insulating grain boundaries, enhancing the dielectric constant while maintaining a low loss. Doping Nd2O3 (0.6-0.8 mol %) and ZrO2 (1-2 mol %) produced a stable material of exceptionally high dielectric constant (~ 50000-100000) and low loss (tan d = 0.03) suitable for high energy density capacitor applications. Grain boundary segregation of ZrO2, the higher solubility of Nd2O3 in ZrO2 than in barium titanate and oxygen diffusion dependent Nd2O3 solubility, were identified as the crucial phenomena involved in modulating the structures of surface and grain boundary barrier layers. The dielectric relaxation mechanisms observed are explained on the basis of brick layer model separating relaxation into Debye and Maxwell Wagner schemes. The model explains the sensitivity of the dielectric properties to the variation of the dimensions of barriers layers and the mode of charge compensation, suggesting that effective medium theories of composite dielectrics do not rule out the possibility of achieving high static dielectric constant at relatively low loss in mixed phase systems such as Nd2O3 and ZrO2 doped barium titanate.
Relva Buchanan, Sc.D. (Committee Chair)
Rodney Roseman, Ph.D. (Committee Member)
Jainagesh Sekhar, Ph.D. (Committee Member)
Vijay Vasudevan, Ph.D. (Committee Member)
168 p.
Materials Science
Barium titanate; Barrier Layer; Neodymium; Dielectric constant; Ceramic capacitors; Zirconium Oxide;

Recommended Citations

Citations

  • Tennakone, H. (2013). Barrier Layer Concepts in Doped BaTiO3 Ceramics [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367937169

    APA Style (7th edition)

  • Tennakone, Harshani. Barrier Layer Concepts in Doped BaTiO3 Ceramics. 2013. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367937169.

    MLA Style (8th edition)

  • Tennakone, Harshani. "Barrier Layer Concepts in Doped BaTiO3 Ceramics." Doctoral dissertation, University of Cincinnati, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367937169

    Chicago Manual of Style (17th edition)

ucin1367937169
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© 2013, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.