Advantages
- Novel monocrystal perovskite oxide material, BNMN (Bi1/2Na1/2) (Mg1/3Nb2/3)O3
- Dielectric constant characteristic is linear with temperature (room temperature to 700 K)
- Highest existing level of precision as temperature sensor (equivalent to platinum thermometer)
Background & Technology
Barium titanate (BaTiO3: hereafter BT) used in multilayer ceramic capacitors (hereafter MLCC) is widely known as a high dielectric material, but BT has a problem that its dielectric properties change significantly by a phase transition near room temperature depending on temperature, making it difficult to use near room temperature. PbTiO3, a typical ferroelectric material, has a simple perovskite structure and a very high dielectric constant, but its properties vary greatly depending on frequency and temperature, and there was no high dielectric constant material that could be used in a wide frequency range under high temperature environments.
In this study, as a method to solve these problems, the inventors replaced Pb at the A site of PbTiO3 with (Bi1/2Na1/2) to form the A-site composite perovskite oxide (Bi1/2Na1/2)TiO3, and replaced Ti at the B site with (Mg1/3Nb2/3) to form the B-site composite The new A/B composite perovskite oxide BNMN was developed, which has both of these properties, because it exhibits relaxor properties with a broad electric susceptibility peak.
BNMN monocrystals were obtained by the self-fluxing method by mixing Bi2O3, Na2CO3, MgO, and Nb2O5 and subjecting them to annealing at 900°C for 4h. Then, BNMN powder was mixed with the flux Bi2O3 and Na2CO3 (mass ratio BNMN : Bi2O3: Na2CO3=1:0.2:0.2). The X-ray measurement revealed that the BNMN crystals have a cubic perovskite structure. The characteristic properties of BNMN shown in Data below indicate that BNMN has a high dielectric constant at room temperature in spite of its normal dielectric constant and linear temperature characteristics, and thus BNMN is expected to be used as a temperature sensor and a high dielectric material that can respond to temperature and frequency changes.
Data
Temperature dependence of dielectric constant and loss of BNMN single crystals
The figure at the bottom shows the dielectric constant of BNMN as a function of loss and temperature from 1kHz to 100kHz; BNMN has a high dielectric constant of 920 at room temperature despite being a normal dielectric (this value far exceeds the c-axis dielectric constant of 109 for BaTiO3 single crystal used in MLCC, and is about half of the a-axis dielectric constant 1970). Furthermore, the dielectric constant does not follow the Curie-Weiss law and exhibits a linear temperature characteristic of ε = 1163-0.829*T.
 |
Researcher
Shizuoka University Department of Electronics and Materials Science
Desheng Fu,Ph.D., Full Professor
Publication
The Ceramics society of Japan 37th Autumn Symposium
Development of new dielectric material (Bi1/2Na1/2) (Mg1/3Nb2/3)O3 single crystal with high dielectric constant
Development Phase
Current stage:
BMNM single crystal fabrication, structural analysis and characterization completed.
Next stage:
・Evaluation of temperature sensor performance by application using this material
・Development and production of capacitors using this material
・Establishment of high-purity BNMN polycrystalline material production process
If there are companies that have needs to use this dielectric material or are interested in collaboration or co-development, performance evaluation, and commercialization of the next stage1. and 2., please feel free to start with a discussion.
Project No.ON-05127