Research

Research contents

Based on experimental research such as material synthesis, evaluation of physical properties, and structural analysis, we are working for creating new materials and for unveiling the origin of physical properties in ferroelectric oxides as the main target material. Ferroelectrics are polar materials with spontaneous polarization (Ps) that can be reversed by an external electric field, and exhibit various properties stemming from their unique structure. We are promoting the following research projects on polar materials including ferroelectrics.

1. Energy conversion by ferroelectric photovoltaic effect (ferroelectric solar cell)

When a ferroelectric is under light illumination, a photovoltaic voltage is generated by a unique phenomenon called the ferroelectric photovoltaic effect. In the photovoltaic effect of a semiconductor pn junction, the generated voltage is limited to the material’s bandgap. In contrast, a voltage that greatly exceeds the bandgap can be generated by the ferroelectric photovoltaic effect. In our laboratory, we are working on enhancing the photovoltaic effect of ferroelectrics by doping impurity elements and controlling their domain structure. In addition to the experimental investigations, theoretical calculations based on the density functional theory are performed to elucidate the mechanisms of the enhanced photovoltaic effect.

Related papers
  • Yuji Noguchi, Yuki Taniguchi, Ryotaro Inoue & Masaru Miyayama, “Successive redox-mediated visible-light ferrophotovoltaics”
    Nature Communications 11, 966 (2020).
    https://doi.org/10.1038/s41467-020-14763-6
  • Hiroki Matsuo, Yuji Noguchi, Masaru Miyayama, Takanori Kiguchi, and Toyohiko J. Konno, “Enhanced photovoltaic effect in ferroelectric solid solution thin films with nanodomain”
    Applied Physics Letters 116, 132901 (2020).
    https://doi.org/10.1063/1.5142880
  • Hiroki Matsuo, Yuji Noguchi, Masaru Miyayama, “Gap-state engineering of visible-light-active ferroelectrics for photovoltaic applications”
    Nature Communications, 8, 207 (2017).
    https://doi.org/10.1038/s41467-017-00245-9

2. Creation of new polar materials

We first discovered a ferrielectric material that exhibits an intermediate property between ferroelectric and antiferroelectric phases. In this research, we are working on the creation of a new material whose dielectric and piezoelectric strain constants are dramatically enhanced by applying an electric field by utilizing the polarization twist mechanism peculiar to the ferrielectric material.

Related papers
  • Yuuki Kitanaka, Masaru Miyayama, and Yuji Noguchi, “Ferrielectric-mediated morphotropic phase boundaries in Bi-based polar perovskites”
    Scientific Reports, 9, 4087 (2019).
    https://doi.org/10.1038/s41598-019-40724-1
  • Yuuki Kitanaka, Kiyotaka Hirano, Motohiro Ogino, Yuji Noguchi, Masaru Miyayama, Yutaka Kagawa, Chikako Moriyoshi, and Yoshihiro Kuroiwa, “Polarization twist in perovskite ferrielectrics”
    Scientific Reports, 6, 32216 (2016).
    https://doi.org/10.1038/srep32216

3. Development of next-generation ferroelectric thin film capacitors

Ferroelectrics have traditionally been used in multilayer ceramic capacitors (MLCCs) and are exploited in many electronic devices. Furthermore, ferroelectric thin films can be used as a non-volatile memory and a capacitor for energy storage, and a dramatic evolution in the performance of ferroelectric materials is required to date. We are developing dielectric materials with performance that surpasses existing materials by controlling lattice defects and stress along with designing superlattice structures.

Related papers
  • Yuji Noguchi, Hiroki Matsuo, Yuuki Kitanaka & Masaru Miyayama, “Ferroelectrics with a controlled oxygen-vacancy distribution by design”
    Scientific Reports, 9, 4225 (2019),
    The top 100 downloaded physics papers for Scientific Reports in 2019.
    DOI: https://doi.org/10.1038/s41598-019-40717-0
  • Yuji Noguchi, Hisashi Maki, Hiroki Matsuo, Yuuki Kitanaka, and Masaru Miyayama, “Control of misfit strain in ferroelectric BaTiO3 thin-film capacitors with SrRuO3 electrodes on (Ba, Sr)TiO3-buffered SrTiO3 substrates”
    Applied Physics Letters, 113, 012903 (2018).
    https://doi.org/10.1063/1.5031156
  • Hiroki Matsuo, Yuuki Kitanaka, Ryotaro Inoue, Yuji Noguchi, and Masaru Miyayama, “Cooperative effect of oxygen-vacancy-rich layer and ferroelectric polarization on photovoltaic properties in BiFeO3 thin film capacitors”
    Applied Physics Letters, 108, 032901 (2016).
    https://doi.org/10.1063/1.4940374

4. Development of solid-state cooling device using polarized structure

Cooling equipment such as air conditioners and refrigerators make up about 10% of Japan’s total power consumption. This heat transport equipment is operated by heat pumps that utilize the compression and expansion of CFC substitutes, and their energy efficiency is limited to be 40–50%. The purpose of this research is to develop solid cooling technology that can be used for next-generation cooling equipment and to provide Japan with innovative measures against global warming. By utilizing the electrocaloric effect derived from the polarization function of polar crystals, we aim to realize a new solid-state cooling technology that is highly energy efficient and does not use greenhouse gases.

Figure　Total amount of CO2 reduced by replacing the conventional heat pump type gas cooling equipment with solid cooling and the effect converted to the operation of the nuclear power plant．

Related papers
  • Yuji Noguchi, “Defect chemistry in perovskite ferroelectrics —History, present status, and future prospects— (SPECIAL ARTICLE)”
    Journal of the Ceramic Society of Japan, 129 [6], 271-285 (2021).
    http://doi.org/10.2109/jcersj2.21039
  • Yuki ICHIKAWA, Yuuki KITANAKA, Takeshi OGUCHI, Yuji NOGUCHI and Masaru MIYAYAMA, “Polarization degradation and oxygen-vacancy rearrangement in Mn-doped BaTiO3 ferroelectrics ceramics”
    Journal of the Ceramic Society of Japan, 122[6], 373-380 (2014).
    https://www.jstage.jst.go.jp/article/jcersj2/122/1426/122_JCSJ-P13226/_article

5. Creation of electric field-induced phase transition materials and development of new functions

The purpose is to develop a new material whose crystal structure changes dramatically when an electric field is applied. In insulating materials under an electric field, the polarization increases to some extent along the field direction and then the system is stabilized. In usual dielectrics, this stabilizing effect is extremely small and almost no effect on the crystal structure is observed. In contrast, for a material that is strategically designed, i.e., its composition and defect structure is strictly controlled near the boundary between two crystal systems with different crystal symmetries, it is expected that the crystal structure can be controlled at will by an electric field.
We have developed a high-quality single crystal of bismuth-based oxide, which is one of a polar material, and succeeded in controlling the ferroelectric phase (space group P4bm) and ferroelectric phase (space group P4mm) by an electric field. In addition, it is revealed that the ferrielectric phase exhibits a piezoelectric strain constant (d33> 1,000 pm/V) far exceeding the currently used lead-based ceramics; our material is a promising candidate for lead-free piezoelectric materials. In addition, by combining with first-principles calculations and thermodynamic phenomenological calculations, we have elucidated the mechanism of the electric field-induced phase transition in which the crystal structure can be controlled by an electric field.

Related papers
  • Yuuki Kitanaka, Kohei Makisumi, Yuji Noguchi, Masaru Miyayama, Akinori Hoshikawa, and Toru Ishigaki, “Composition-driven structural variation in ferrielectric phase of (Bi1/2Na1/2)TiO3–Ba(Mg1/3Nb2/3)O3”
    Japanese Journal of Applied Physics, 58, SLLA04 (2019).
    https://doi.org/10.7567/1347-4065/ab37c4
  • Yuuki Kitanaka, Masaru Miyayama, and Yuji Noguchi, “Ferrielectric-mediated morphotropic phase boundaries in Bi-based polar perovskites”
    Scientific Reports, 9, 4087 (2019).
    https://doi.org/10.1038/s41598-019-40724-1
  • Yuuki Kitanaka, Takuya Egawa, Yuji Noguchi, and Masaru Miyayama, “Enhanced Polarization Properties of Ferrielectric AgNbO3 Single Crystals Grown by Czochralski Method under High-Pressure Oxygen Atmosphere”
    Japanese Journal of Applied Physics, 55, 10TB03 (2016).
    http://doi.org/10.7567/JJAP.55.10TB03

6. Elucidation of the electronic mechanism of polar-driven functions

The various functions of materials are derived from the behavior of electrons. By making full use of first-principles calculations and thermodynamic calculations, we elucidate the mechanism of the functions in polar materials in terms of electronic structures.
So far, in Bi-based ferroelectrics, the rhombic crystal (space group R3c) is stabilized in the Bi-Na system, and the tetragonal crystal (space group P4mm) is stabilized in the Bi-K system, but the mechanism is unknown. Through experiments for high-quality single crystals and first-principles calculations, we found that the orbital hybridization of Bi-6p and O-2p electrons play an important role in the stability of the systems.

Related papers
  • Yuuki Kitanaka, Yuji Noguchi, and Masaru Miyayama, “Uncovering ferroelectric polarization in tetragonal (Bi1/2K1/2)TiO3–(Bi1/2Na1/2)TiO3 single crystals”
    Scientific Reports 9, 19275 (2019).
    doi:10.1038/s41598-019-55576-y
  • Tomohiro Abe, Sangwook Kim, Chikako Moriyoshi, Yuuki Kitanaka, Yuji Noguchi, Hiroshi Tanaka and Yoshihiro Kuroiwa, “Visualization of spontaneous electronic polarization in Pb ion of ferroelectric PbTiO3 by synchrotron-radiation X-ray diffract Visualization of spontaneous electronic polarization in Pb ion of ferroelectric PbTiO3 by synchrotron-radiation X-ray diffraction ion”
    Applied Physics Letters, 117, 252905 (2020).
    https://doi.org/10.1063/5.0037396
  • Yuji Noguchi, “Defect chemistry in perovskite ferroelectrics —History, present status, and future prospects— (SPECIAL ARTICLE)”
    Journal of the Ceramic Society of Japan, 129 [6], 271-285 (2021).
    http://doi.org/10.2109/jcersj2.21039

Research Facilities

1. Pulsed laser deposition (PLD)

This is a facility in which a target material installed in the vacuum chamber is turned into plasma by a pulsed laser and a thin film is deposited on the opposite substrate. This is used to fabricate epitaxial films of dielectrics and ferroelectrics.

2. TSSG（Top-Seeded Solution Growth）furnace

This is a furnace that enables us to grow single crystals by using a seed crystal. In particular, it is possible to grow single crystals under high oxygen pressure of nine atm, and high-quality ferroelectric single crystals with low defect concentration can be obtained.

3. Multipurpose X-ray diffractometer

This is an XRD facility for analyzing crystal structures and domain structures of epitaxial thin films. In addition to high-resolution reciprocal lattice mapping using a high-speed one-dimensional detector, wide-area reciprocal lattice mapping and pole-figure measurements using a two-dimensional detector are available.

4. X-ray fluorescence analyzer

This is a facility to quantify the composition of samples in ceramic, single-crystal and film forms.

5. Desktop X-ray diffractometer

XRD diffractometer for powder samples.

6. Muffle furnace

Electric furnaces for sample preparation.

7. Quench furnace

An annealing/quenching furnace in which oxygen partial pressure can be controlled.

8. Ferroelectric measurement system

This system enables us to evaluate polarization, piezoelectric and leakage-current characteristics.

9. Photovoltaic effect measurement system

This system enables us to evaluate photovoltaic characteristics under light with a controlled wavelength.

10. Low/high temperature prober

A prober for measuring electrical properties of samples using microelectrodes.

11. Ultraviolet-visible spectrophotometer

A spectrophotometer capable of measuring transmission / reflection spectrum in the ultraviolet / visible light region. Powder diffuse reflection spectrum measurements are also available.

12. Glove box

Experiments in an inert atmosphere and low dew point environment are possible. It is used for strict weighing of hygroscopic reagents.

13. Atomic force microscope, piezoresponse force microscope

It is a probe microscope that can observe a surface morphology at the atomic scale. Domain structures of ferroelectrics can also be observed by a contact resonance piezoresponse method.