Application of Rare Earth in New Functional Ceramic Materials

- Nov 16, 2017 -


1. In the superconducting ceramic applications


Since 1987, China, Japan, the United States and other countries found that YBCO oxide ceramics with excellent high temperature superconductivity (Tc up to 92K), people in the rare earth high temperature superconducting ceramic performance research and application development A great deal of work has been done and many great progress has been made. In Japan, studies have shown that the critical magnetic field strength of the obtained superconducting ceramic material LnBCO after replacing Y in YBCO with light rare earths (Nd, Sm, Eu, Gd) Significantly increased, flux pinning force is also greatly enhanced, in the power, energy storage and transportation and other areas of great practical value. For example, a LnBCO block made by a certain production process can capture a magnetic field larger than 10T at 77K, and can be used as a magnet of a maglev train instead of Nd-Ti.


Peking University, with ZrO2 as the substrate and heated to about 200 ℃, Y (or other rare earth), Ba oxide and Cu were separately evaporated on the substrate to be diffused, and then heat-treated at 800 ~ 900 ℃, The resulting superconducting ceramic exhibits a good metallic temperature coefficient of resistance above 100K. Kagoshima University of Japan doped rare earth La into Sr, Nb oxide ceramic thin film made in the 255K superconductivity occurs.



2 in the piezoelectric ceramic applications


Lead titanate (PbTiO3) is a typical piezoelectric ceramic with mechanical energy-energy coupling effect. Its high Curie temperature (490 ℃) and low dielectric constant make it suitable for high temperature and high frequency applications. However, in the process of its preparation and cooling, due to produce cubic - tetragonal phase change prone to micro-cracks. In order to solve this problem, RE-PbTiO3 ceramics with a relative density of 99% can be obtained by modifying with rare earth. The microstructure of the RE-PbTiO3 ceramics can be obviously improved and can be used to manufacture RE-PbTiO3 ceramics with high frequency of 75MHZ Transducer array for work. The analysis shows that due to the RE3 + substitution of rare earth ions, the dielectric constant of PbTiO3 ceramics is reduced and the piezoelectric anisotropy (kt / kp) is enhanced, which is especially suitable for transducers in electronic scanning medical ultrasound system. And due to the ceramic dielectric constant and radial electromechanical coupling coefficient decreases, the high frequency resonance peak becomes simple, conducive to the manufacture of high sensitivity, high resolution ultrasonic transducer.


In PZT piezoelectric ceramics with high piezoelectric coefficient, the sintering properties of PZT ceramics can be obviously improved and the stable electrical and piezoelectric properties can be obtained by adding rare earth oxides such as La2O3, Sm2O3 and Nd2O3. , This is because the use of trivalent La3 +, Sm3 +, Nd3 + and other rare earth ions to replace the PZT in the A position of Pb2 +, the PZT ceramic electrical physical characteristics of a series of changes. In addition, the performance of PZT ceramics can also be improved by adding a small amount of rare earth oxide CeO2, and the addition amount of CeO2 is preferably 0.2% ~ 0.5%. The volume resistivity of PZT ceramics increases with the addition of CeO2, which is conducive to the process of polarization under high temperature and high electric field, and its anti-aging and anti-aging properties are also improved. The rare earth-modified PZT ceramic has been widely used in high voltage generator, ultrasonic generator, underwater acoustic transducer and other devices.


3 in the conductive ceramic applications


Yttria-stabilized zirconia (YSZ) ceramics with rare earth oxide Y2O3 as additive have good thermal stability and chemical stability at high temperature, and are good oxygen ion conductors and have prominence in ion-conductive ceramics. YSZ ceramic sensor has been successfully used to measure the partial pressure of oxygen in the vehicle exhaust, effectively control the air / fuel ratio, energy-saving effect is remarkable, in the industrial boiler, smelting furnace, incinerator and other combustion-based equipment has been widely used. YSZ ceramic can also be used as a high temperature solid oxide fuel cell (SOFC) electrolyte material, the use of more Zr0.9Y0.1O1.95. Since SOFC uses a solid electrolyte, there is no problem of electrolyte treatment involved in other fuel cells, and the conversion efficiency is close to 60%. In addition, rare earth doped LaCr0.9Mg0.1O3, La0.85Sr0.15MnO3 ceramic and Ni-Zr (Y) O2-X cermet thin layer can also be used as bipolar plates in SOFC cells, porous Cathode and porous anode material.


However, YSZ ceramics exhibit higher ionic conductivity only above 900 ° C, so its application is still limited. It has been found in the prior art that Bi2O3 face-centered cubic phase can be stabilized to room temperature by adding appropriate amount of Y2O3 or Gd2O3 to Bi2O3 ceramics with higher ion conductivity, and the X-ray diffraction pattern of (Bi2O3) 0.75 · (Y2O3) 0.25 and (Bi2O3) 0.65 · (Gd2O3) 0.35 are stable face-centered cubic oxygen ion conductive phases. After the side of the ceramic is coated with a protective film of (ZrO2) 0.92 (Y2O3) 0.08, a fuel having high ionic conductivity, good stability and capable of operating at a medium temperature (500 to 800C) can be prepared Battery and oxygen sensor, help solve the problems caused by high temperature technology.


4. In the application of dielectric ceramics


Dielectric ceramic is mainly used for making ceramic capacitors and microwave dielectric components. In TiO2, MgTiO3, BaTiO3 and other dielectric ceramics and their composite dielectric ceramics, the addition of La, Nd, Dy and other rare earth can significantly improve the dielectric properties.


If BaTiO3 ceramics with high dielectric constant are added, the La and Nd rare earth compounds with the permittivity ε = 30-60 can keep their dielectric constant stable over a wide temperature range, and the service life of the device is greatly improved. In the thermal compensation capacitor dielectric ceramic, rare earth can also be properly doped as needed to achieve the ceramic dielectric constant, temperature coefficient, quality factor improvement or regulation, expand its scope of application. Using La2O3 to modify the MgO · TiO2-La2O3-TiO2 ceramics and CaTiO3-MgTiO3-La2TiO5 ceramics, the characteristics of the original dielectric loss and temperature coefficient are kept unchanged , The dielectric constant has also been significantly improved.


A wide range of microwave dielectric ceramics, doped with rare earth oxide BaO-RE2O3-TiO2 ceramic is a more common dielectric material, the dielectric constant ε can be more than 80. Such as MgTiO3-CaTiO3-La2O3 ceramic Qf value of up to 8000, and Nd2Ti2O7- (BaPb) TiO3-TiO2 ceramic dielectric constant ε can reach 90. Due to the application of new technologies, with the development of new ceramics such as BaO-TiO2-SnO2-RE2O3 series, the main technical indexes of microwave ceramic dielectric materials are expected to reach in recent years: the Q? Value is about one order of magnitude higher than that of the present, 10000; ε is serialized in the range of 2 ~ 2000 for a variety of purposes; and the temperature coefficient αε is serially changed in the range of 300 ~ -100, microwave devices such as dielectric resonators and filters with zero temperature coefficient can be obtained more conveniently .


5 in the application of sensitive ceramics


Sensitive ceramics is an important kind of functional ceramics, which is characterized by being sensitive to certain external conditions such as voltage, gas composition, temperature, humidity and the like. Therefore, the response to or change in the relevant electrical performance parameters can be used to realize the circuit, operation Process or environmental monitoring, widely used in control circuit sensing element, it is also known as the sensor ceramic. There is a close relationship between the properties of rare earths and the properties of these ceramics.


(1) electro-optical ceramic


In PZT added rare earth oxide La2O3, you can get transparent lead zirconate titanate (PLZT) optoceramics. The original parent material PZT is generally opaque due to the existence of pores, grain boundary phases and anisotropy, while the addition of La2O3 makes the microstructure more uniform and largely eliminates the pores, weakens the anisotropy and significantly reduces The light scattering caused by multiple refraction on the grain boundary and the light scattering caused by the second phase make the PLZT have a good light transmission performance. PLZT electro-optic ceramic there is a photoelectric effect (Bourke effect), secondary electro-optical effect (Kerr effect) and light scattering effect and optical memory effect, in which the Kerr effect is the most common application, such as shielding nuclear radiation goggles Heavy bomber windows, optical communication modulators, holographic recording devices and the like. As PLZT electro-optic ceramic has the characteristics of using the electric field to change its optical properties, its appearance marks the true entry of ceramic materials into the field of functional optics.


(2) pressure-sensitive ceramic


Central South University of Technology has studied the influence of rare earth elements on the electrical properties of ZnO varistor ceramics. The varistor voltage VlmA increased significantly with La2O3 doped with ZnO varistor ceramics. When the doping amount increased from 0.1% By 10%, the ceramic non-linear coefficient α decreased from 20 to 1, basically no pressure-sensitive properties. Therefore, for ZnO ceramics, low-concentration rare earth elements can increase the voltage-sensitive voltage value when doped with rare earth elements, but have little effect on the nonlinearity coefficient. However, the ceramic with high concentration does not exhibit pressure-sensitive characteristics.


(3) gas-sensitive ceramics


Since the 1970s, many studies have been done on the role of rare earth oxides in gas-sensing ceramic materials such as ZnO, SnO2 and Fe2O3, and ABO3-type and A2BO4-type rare earth composite oxide materials have been prepared. Some studies have shown that the addition of rare earth oxides in ZnO can significantly improve its sensitivity to propylene; SnO2 doped with CeO2 can be obtained ethanol-sensitive sintered components.


Dalian University of Technology The properties of REFeO3 series materials doped with rare earth oxide RE2O3 (RE = Nd, Sm, La) were studied. It is pointed out that the ultrafine particles are an important factor to improve the sensitivity of gas sensors. The effects of different rare earth elements on the micro-morphology of the materials are also different. The particle size of NdFeO3 and SmFeO3 is smaller and the particle size of LaFeO3 is slightly larger. The measured REFeO3 series gas sensors were analyzed in 0.13% concentration of different atmosphere and found that REFeO3 series of materials have higher sensitivity to ethanol, and the order of their sensitivity is NdFeO3> SmFeO3> LaFeO3, while the sensitivity to gasoline Lower, almost no reaction to other gases, it has a strong selectivity.


(4) Thermal ceramics


Barium titanate (BaTiO3) is currently the most studied and most widely used thermal ceramics. When BaTiO3 is doped with rare earth elements such as La, Ce, Sm, Dy, Y and the like (molar atomic fraction control is 0.2% ~ 0.3%), part of Ba2 + is substituted by RE3 + , The resistivity of the ceramic is significantly reduced. However, if the doping amount exceeds a certain value (for example, the mole fraction of doped La> 0.35%), the formation of Ba2 + vacancies And the disappearance of conductive carriers, the electrical resistivity of the ceramic instead of sharp rise, and even become an insulator.


(5) Humidity-sensitive ceramics


In a wide range of humidity-sensitive ceramics, the current rare earth doped mainly lanthanum and its oxides, such as Sr1-xLaxSnO3 system, La2O3-TiO2 system, La2O3-TiO2-V2O5 system, Sr0.95La0.05SnO3 and Pd0.91La0. 09 (Zr0.65Ti0.35) 0.98O3-KH2PO3 and the like. In order to further improve the sensitivity of humidity ceramics, in the nature and stability, in order to enhance its practicality, but also need to strengthen the rare earth doped ceramics related performance impact studies.

Article from NdFeB Industry Network

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