[14p-421-1~12] 9.1 Dielectrics, ferroelectrics

[14p-421-5] [JSAP Young Scientist Award Speech] Development of Conductor / Insulator Fine-composites Prepared by Low-temperature Processes

〇Shintaro Ueno¹, Yuya Hattori¹, Hiroyuki Kakiuchi¹, Kouichi Nakashima², Satoshi Wada¹ (1.Univ. of Yamanashi, 2.Ibaraki Univ.)

Keywords:Dielectrics, Composites, Low-temperature process

To develop ultrahigh-capacitance capacitors, we have focused on boundary layer (BL) capacitors which can exhibit a high dielectric constant over 10⁴. BL capacitors commonly consist of semiconductor grains and insulated grain boundaries with a thickness of a few nanometers. We tried to replace semiconductor layers with conductor layers such as metals and conductive oxides and develop conductor/insulator composite capacitors with BL structures. To avoid oxidization of metal layers or formation of solid solution between conductive-oxide and insulators, we proposed the low-temperature processes including solvothermal method for preparation of conductor/insulator composite capacitors. The microstructures of the BL capacitors can be seen as the assembly of conductor-insulator core-shell components. That means the BL capacitors can be fabricated by the conductor-insulator core-shell particles. For the case of metal/insulator perovskite oxide composites, The titanium metal/barium titanate (Ti/BT) composites consisting of Ti metal grains and BT boundary nanolayers were successfully prepared from the pressed Ti-BT core-shell particle compacts with various thicknesses of the BT shell layers by the hydrothermal method below 230 °C. The thickness of insulator shell layers and the resultant insulator boundary nanolayers can be precisely controlled by solvothermal conditions, and the effective dielectric constant increases up to over 10⁴ with a decrease in the thickness of insulated boundary nanolayers for Ti/BT composite capacitors. We have been also trying to fabricate the lanthanum nickelate (LN)/insulator composite with the BL structures. The LN polyhedral particles were synthesized by the sol-gel-flux method using the modified molten salts and were coated with insulator layers by the liquid process. In this case, when the perovskite-oxide insulator with appropriate lattice parameter is selected, the epitaxial insulator layers are possible to form on the conductive perovskite oxide LN polyhedral particles. We believe that the introduction of the epitaxial layers in the conductor/insulator interface is expected to improve the dielectric breakdown strength of the composite capacitors. Now, LN particles could be partially coated with aluminum oxide nanoparticles by the interface-chemistry approach.