Researchers from the Shibaura Institute of Technology have made a significant breakthrough in the development of ferroelectric materials by successfully synthesizing rubidium niobate (RbNbO3), a compound previously deemed challenging to produce under pressures exceeding 40,000 atmospheres. This novel displacement-type ferroelectric material exhibits remarkable dielectric properties and offers new design guidelines for ferroelectric materials. Capacitors, essential components in electronic devices like smartphones and computers, rely on dielectric materials that polarize in the presence of voltage. Barium titanate (BaTiO₃) is currently the most widely used material for capacitors, showcasing displacive-type ferroelectric behavior.
In a study published in the journal Dalton Transactions, researchers led by Professor Ayako Yamamoto from the Shibaura Institute of Technology, along with master student Kimitoshi Murase and Dr. Hiroki Moriwake’s group from the Japan Fine Ceramics Center, developed a displacement-type ferroelectric material with a high dielectric constant. By employing a high-pressure method, they successfully incorporated sizable rubidium ions into perovskite-type compounds, leading to the synthesis of RbNbO3. This compound’s synthesis has been challenging in the past, but the innovative approach used in this study has proven successful. RbNbO3 exhibits characteristics similar to BaTiO3, making it a promising candidate for capacitors.
The researchers synthesized non-perovskite-type RbNbO3 by sintering a mixture of rubidium carbonate and niobium oxide at 800°C, then subjecting it to high pressures of 40,000 atmospheres at 900°C for 30 minutes. Under these conditions, RbNbO3 underwent a structural transformation from a triclinic phase to a denser orthorhombic perovskite-type structure. Through X-ray diffraction, the crystal structure of RbNbO3 was investigated, showing similarities to KNbO3 and BaTiO3 but with higher orthorhombicity and niobium atom displacement, resulting in enhanced dielectric polarization due to phase transitions.
Researchers identified four distinct phase transitions in RbNbO3 occurring over a temperature range of -268°C to +800°C, with an orthorhombic phase being the most stable configuration below room temperature. Predictions made through first-principles calculations aligned with observed phase transitions, showing dielectric polarization values of 0.33 C m−2 for the orthorhombic phase, 0.4 and 0.6 C m−2 for the tetragonal phases, comparable to other ferroelectric alkali metal niobates. The potential for RbNbO3 to exhibit high dielectric constant and polarization makes it a promising material for further study and development.
The high-pressure synthesis method used in this study shows promise in stabilizing substances that do not exist under atmospheric pressure, allowing for the incorporation of larger alkali metal ions like cesium into the perovskite structure. This could lead to the development of ferroelectrics with desirable dielectric properties. Future experiments will focus on accurately measuring the dielectric constant and demonstrating the high polarization of RbNbO3, paving the way for advancements in ferroelectric material research and potential applications in electronic devices. The innovative approach and successful synthesis of RbNbO3 by the researchers hold significant implications for the field of materials science.