Barium titanate ceramics are ceramic materials with barium titanate (BaTiO3) or its solid solution as the main crystal phase. The main raw materials are barium carbonate and titanium dioxide. Generally, barium titanate is synthesized at 1200℃ first, and then modified oxide is added. After fine grinding, it is sintered at 1400℃ or so. Used as dielectric material of capacitor and make many kinds of piezoelectric devices
Barium titanate ceramics are ceramics with barium titanate or its solid solution as the main crystal phase. With a perovskite structure of ABO3, it is a typical ferroelectric material with the molecular formula BaTiO3. BaCO3 and TiO2 as the main raw materials were synthesized in advance and sintered at 1280 ~ 1400℃. Or high purity super fine barium titanate powder prepared by chemical method can be burned directly after forming. The artificial high voltage polarization has piezoelectric properties, its electromechanical coupling coefficient (Kp) 0.36, quality factor (Qm) 300, the piezoelectric constants d31 and d33 reach -80× 10-12c /N and 190× 10-12c /N respectively, the Curie temperature is 120℃, used for making piezoelectric devices. It can be modified by adding peak-shifting agent or peak-pressing agent. Barium titanate semiconductor ceramics can be prepared by forced reduction or donor doping method, which can be used to manufacture ferroelectric capacitors, positive temperature coefficient (PTC) thermal sensitive elements, surface layer capacitors and various piezoelectric devices
Mechanism of barium titanate materials
As famous ferroelectric and piezoelectric material, BaTIO3 as early as in 1942 has been found by beauty, Su Xuezhe, one is by far the most thorough material, and in the view of modern, BaTIO3 the electrical properties of piezoelectric ceramic and less pollution is one of the important factors, the respected by people again so BaTIO3 is also the important candidate for the preparation of lead-free piezoelectric ceramic materials at present. At present, the research of BaTIO3 piezoelectric ceramics is mainly focused on the bivariate or multielement ceramic system based on BT.
BaTiO3 belongs to ABO3 type of calcium deposit structure (as shown in figure 1). With the change of temperature, BaTiO3 undergoes the following phase transition process: cubic phase, electrical phase ~120℃, quadonal phase ~5℃, normal phase ~ 80℃, three-way phase. At room temperature, it has a strong piezoelectric ferroelectricity, showing a strong spontaneous polarization along the c axis, the spontaneous polarization value is 26×10-12 c /cm2. When the temperature is higher than 120℃, BaTIO3 crystal belongs to cubic crystal system, and the piezoelectric ferroelectric properties disappear
BaTIO3 ceramic is a mature lead-free piezoelectric ceramic material, which has high dielectric constant, large coupling coefficient and piezoelectric constant, medium mechanical quality factor and small dielectric loss. However, the Curie temperature is low (Tc=120℃), the working temperature range is narrow, and there is a phase change near room temperature, that is, BaTIO3 ceramics at 5℃, the ferroelectric quadric phase (4mm) to ferroelectric normal phase (Zmm) transformation, which is inconvenient to use, can not be used for high-power transducers. At the same time, the temperature and time stability of the piezoelectric properties of the ceramic is not good, and the sintering is difficult (generally from 1300℃ to 1350℃), so it is difficult to improve its properties through doping modification to meet different needs
Since the discovery of piezoelectric properties of barium titanate ceramics in the 1940s, piezoelectric ceramics have been developed for more than 60 years. Piezoceramics, as a kind of important functional materials with fierce international competition, has been applied in every corner of human production and life. However, most of the traditional piezoelectric ceramics are lead-containing ceramics, in which lead oxide (or lead tetroxide) accounts for about 70% of the total quality of raw materials, which will bring harm to the environment and human beings in the process of preparation, use and waste treatment. From the perspective of ecological environment protection and the implementation of social sustainable development strategy, the lead free development of piezoelectric ceramics is the inevitable trend of its development. Type ABO3 perovskite BaTiO3 (BT) is the earliest lead-free piezoelectric ceramic and the first applied piezoelectric ceramic material.
Barium titanate crystals have a common characteristic of piezoelectric materials: when they change shape under pressure, an electric current is generated, which changes shape when energized. So people put barium titanate in an ultrasonic wave, and when it was pressed, a current was generated. By contrast, a high-frequency current can be passed through it to produce ultrasonic waves. Now, in almost all ultrasound machines, barium titanate is used. In addition, barium titanate has many USES. For example, a railroad, which workers place under the tracks to measure the pressure of a train as it passes by; Doctors used it to make a pulse recorder. The underwater detector made of barium titanate is a sharp underwater eye. It can not only see schools of fish, but also see reefs, icebergs and enemy submarines