How to improve the pyroelectric coefficient of crystals, what is the pyroelectric effect principle

The basic ones are to look at the physical properties of this material, and if you want to understand it in detail, go to this book about pyroelectric materials to see pyroelectric materials.

pyroelectric materialA crystalline material with spontaneous polarization properties. Spontaneous polarization refers to the intrinsic polarization due to the fact that the structure of the substance itself does not coincide with the centers of positive and negative charges in a certain direction. In general, the surface-bound charge generated by the spontaneous polarization of the crystal is shielded by the free charge adsorbed on the crystal surface, and when the temperature changes, the spontaneous polarization changes, thereby releasing part of the charge adsorbed on the surface.

The polarity of the charge when the crystal is cooled is opposite to that when heated. Pyroelectric materials are piezoelectric materials that are crystals that do not have central symmetry. There are thousands of materials with pyroelectric properties, but only a dozen are widely used, mainly triglycoside sulfate peptides, lead lanthanum zirconate titanate, transparent ceramics and polymer films.

Pyroelectric materials can be used in industry as infrared detection devices, thermal camera tubes and have certain special uses in national defense. It has the advantage that it does not require cryogenic cooling, but its sensitivity is lower than that of the corresponding semiconductor devices.

There are positive and negative charges, with positive charges denoted by a "+" sign and negative charges denoted by a "-" sign. Generally speaking, it is fixed which end of a charged substance produces a positive charge and which end produces a negative charge. However, some crystals have a charge reversal phenomenon, that is, when heated, one end produces a positive charge and the other end produces a negative charge, and when cooling, the end that originally generated a positive charge produces a negative charge, and the end that originally generated a negative charge produces a positive charge.

These crystals are called pyroelectric crystals. Mercury cadmium telluride crystals are one of these pyroelectric crystals.

In some insulating substances, the phenomenon of a change in the polarization state due to a change in temperature is called the pyroelectric effect. Substances that can achieve pyroelectric effects are called thermoelectrics. Thermoelectric substances include triglycerin sulfate (TGS), ferroelectric barium titanate, tourmaline and sucrose.

The phenomenon was discovered 2,300 years ago, but research on it began in the 18th century. It is now one of the most active research areas in solid state physics. Because the pyroelectric coefficient of ferroelectric is much larger than that of general thermoelectrics, it has become a widely used thermoelectric material, in addition to TGS and its derivatives, ferroelectric ceramics (such as PZT, PLZT, etc.) have become practical thermoelectric materials that are easy to change the control performance by composition, suitable for mass production, and inexpensive.

The pyroelectric effect has been used in pyroelectric infrared detectors in the past 10 years, and is widely used in radiation and non-contact temperature measurement, infrared spectroscopy measurement, laser parameter measurement, industrial automatic control, space technology, and infrared photography. China's infrared camera tubes made of ATGSAS crystals have begun to be exported abroad. Its temperature response rate reaches 4 5 A, the temperature resolution is less than that, the signal sensitivity is high, the image clarity and anti-strong light interference ability are also significantly improved, and the hysteresis is small.

In addition, since pyroelectric phenomena also exist in living organisms, it can be expected that the pyroelectric effect will have important applications in living organisms and even in life processes.

To understand the pyroelectric effect, I think you need to have a certain foundation in piezoelectric ceramics and solid state physics. I'll let you know the definition first, and if you have any questions, please ask.

pyroelectric effect

Due to the change of temperature, pyroelectric crystals and piezoelectric ceramics will have a relative displacement of the charge center on the structure, which will change their spontaneous polarization intensity, resulting in a binding charge with a different sign at both ends of them, a phenomenon called pyroelectric effect. Materials that have this property are called pyroelectrics. Piezoelectric ceramics belong to pyroelectric bodies.

Regardless of temperature inhomogeneity, pyroelectric bodies generally have primary and secondary pyroelectric effects. Among them, the second-order pyroelectric effect is the second-order effect in which the material is deformed due to temperature change, and then the charge is generated by the piezoelectric effect. In general, if the rate of temperature change is the same, the pyroelectric charges generated during the ramp and fall are of equal magnitude but with opposite signs.

1 Polarization

The polarization of the dielectric is called the polarization of the dielectric when the charge bound in the dielectric is displaced or the polarity rotates in the direction of the electric field under the action of an electric field.

2 Spontaneous polarization

In the absence of an external electric field, there is polarization in ferroelectric crystals or ferroelectric ceramics due to the orderly arrangement of electric dipoles, which is called spontaneous polarization. On a surface perpendicular to the axis of polarization, the amount of spontaneously polarized charge per unit area is called the spontaneous polarization intensity. It is a vector quantity, denoted by p, and its unit is c m2.

3 piezoelectric effect

The application of mechanical force to certain dielectrics causes the relative displacement of the centers of positive and negative charges within them, resulting in polarization, resulting in the appearance of bound charges with opposite signs on the surface of the dielectric at both ends. Within a certain range of stress, the mechanical force has a linearly reversible relationship with the electric charge, a phenomenon known as the piezoelectric effect or the positive piezoelectric effect. On the contrary, if the medium with piezoelectric effect is placed in an external electric field, the action of the electric field will cause the displacement of the center of positive and negative charges inside the medium, and this displacement will deform the medium.

Within a certain range of electric field strength, the electric field strength has a linear reversible relationship with the deformation, and this effect is called the inverse piezoelectric effect.

The pyroelectric effect refers to the phenomenon of charge release exhibited by the change of polarization intensity with temperature, and macroscopically it is the change of temperature that causes a voltage or current to occur at both ends of the material.

There are positive and negative charges, with positive charges denoted by a "+" sign and negative charges denoted by a "-" sign. Generally speaking, it is fixed which end of the charged substance produces a positive charge and which end produces a negative charge. However, some crystals will have a charge reversal phenomenon, that is, when heated, one end produces a positive charge, and the other end produces a negative charge, and when cooling, the original positive charge of one end of the auspicious slag accompaniment produces a negative charge, and the original end of the negative charge produces a positive charge.

These crystals are called pyroelectric crystals. Mercury cadmium telluride crystals are one of these pyroelectric crystals.

The pyroelectric effect is similar to the piezoelectric effect, which is also a natural physical effect of crystals. For crystals with spontaneous polarization, when the crystal is heated or cooled, the phenomenon of spontaneous polarization intensity change (ps) due to the change of temperature (t), resulting in a surface polarization charge in a certain direction of the crystal is called pyroelectric effect. The relationship can be expressed in a formula.

ps=p△t

where ps is the change in spontaneous polarization intensity; t is the temperature change; p is the pyroelectric coefficient.

The pyroelectric effect was first found in tourmaline crystals (Na, Ca) (Mg, Fe)3B3Al6Si6(O, H, F)3, which belong to the trigonal crystal system and have a single triple axis of rotation. As with piezoelectric crystals, the pyroelectric effect of crystals presupposes spontaneous polarization, i.e., the presence of an intrinsic moment in a certain direction. However, piezoelectric crystals do not necessarily have a pyroelectric effect, whereas pyroelectric crystals must have a piezoelectric effect.

Pyroelectric crystals can be divided into two main categories. One type has spontaneous polarization, but spontaneous polarization is not steered by external electric fields. Another type of spontaneously polarized crystal that can be steered by an external electric field is ferroelectric.

Because this type of crystal has macroscopic residual polarization after pre-polarization, and its residual polarization changes with temperature, the surface charge can be released, showing a pyroelectric effect.

Normally, the binding charge generated by the spontaneous polarization of the crystal is neutralized by the free electrons in the air that are attached to the outer surface of the crystal, and its spontaneous polarization moment cannot be displayed. When the temperature changes, the center of gravity of the positive and negative charges in the crystal structure will be shifted relatively, and the spontaneous polarization value of the crystal will change, and the charge will be exhausted on the crystal surface.

Crystals that produce pyroelectric effects are called pyroelectrics, also known as thermoelectric elements. Commonly used materials for thermoelectric components include single crystal (Litao3, etc.), piezoelectric ceramics (PZT, etc.), and polymer thin films (PVF2, etc.).

If resistors are connected in parallel at both ends of the thermoelectric element, when the element is heated, current flows through the resistor, and a voltage signal can be obtained at both ends of the resistor.

Theoretically, even if the object itself cannot be seen, as long as Hu can observe the infrared rays emitted by it, it is possible to accurately determine its position and determine its size, shape, and other characteristics. Since pyroelectric crystals are sensitive to heat, they are suitable for this task. Now a large number of infrared night vision devices are equipped with military ** is made of pyroelectric components made of pyroelectric crystals and other electronic, mechanical and other components.

It's amazing.