what's the polarization method of piezoelectric ceramic

(1)Oil bath polarization method

The oil bath polarization method is a method in which a product such as methyl silicone oil is used as an insulating medium to polarize a product under a certain polarization electric field, temperature and time. Due to the wide temperature range, high dielectric strength and good moisture resistance of methyl silicone oil, the method is suitable for piezoelectric ceramic materials with high polarization electric field.

(2) Gas polarization method

The air polarization method is a method in which air is used as an insulating medium to polarize a product under the certain polarization conditions. The method is simple in operation because the insulating oil is not used, and the polarized product is not clean, so the cost is low. Due to the low air breakdown field strength (3kV/mm), this method is especially suitable for soft PZT materials with lower coercive field strength. For materials with an EC of 0.6KV/mm, the polarization electric field is 2EC of 1.2KV/mm, and the 3EC is 1.8KV/mm, which is much lower than the breakdown strength of the air medium, piezoelectric disc vibration sensor can achieve the same polarization as the oil bath effect. Under the conditions of increasing the polarization temperature and prolonging the polarization time, the method can also be adapted to the polarization of a product having a reduced breakdown field strength and a sheet product is having difficulty in high-pressure polarization.

(3)High temperature air polarization method

The high-temperature polarization method of air is based on air as the insulating medium. The polarization temperature of ultrasonic piezoelectric ceramic transducer is gradually reduced from above the curie temperature (above TC10-20 °C) to below 100 °C, and the corresponding polarization electric field is gradually weaker (about 30 V/mm). The method of increasing the intensity (about 300 V/mm) and polarizing the product is also called high temperature polarization or thermal polarization. The principle of the method is that an electric field is applied before the formation of the ferroelectric phase of the product, so that the paraelectric-ferroelectric phase transition is performed under the action of an applied electric field, and the domain is oriented in the direction of the external field as soon as it appears. Since the domain motion is easy at the high temperature and the crystal anisotropy is small, the resistance of the domain for non-180o steering is small, and the stress strain is small. Therefore, a very low electric field can obtain a highly polarized electric field at a low temperature. The method has the characteristics of small polarization electric field, there is no need of high DC electric field equipment, there is no cracking of insulating oil and products. It is suitable for piezoelectric ceramic element with large polarization (such as the power generation part of piezoelectric step-up transformer) and high voltage in the common polarization.