WO2017204672A1 - Ferroelectric ceramics - Google Patents

Abstract

The invention relates to ceramic materials used in electronic engineering, and particularly radio-frequency engineering, and may be applied for creating antennas in the ultrahigh-frequency (UHF) range, and controlled elements having high speed, low power in control circuits, and having low production costs. Ferroelectric ceramics for preparing antennas in the UHF range based on barium titanate (BaTiO₃) and barrium zirconate (BaZrO₃) includes a bismuth silicate additive (Bi₂SiO₅) with the following ratio of components, by mass%: BaTiO₃: 85.5-85.7; BaZrO₃ = 5.3-5.8; Bi₂SiO₅ = 8.5-9.1. Carrying out the invention allows for producing ferro-ceramic materials for antennas in the UHF range which do not contain dangerous components, namely oxides of lead and of strontium, with a relative change in dielectric permittivity, in a temperature range of -60 ÷ +60°C, of no more than ±20%.

Description

 Ferroelectric Ceramics

The invention relates to ceramic materials used in electronic engineering, in particular radio engineering, and can be used to create microwave antennas, controlled elements with high speed, low power in control circuits, which have a low production cost.

 Such materials include ferroelectric materials with a very high relative permittivity, which can significantly reduce the linear dimensions of the antennas due to the formation of an effective excitation zone in the body of the ceramic element. The physical phenomenon that allows creating such elements is based on the dependence of the dielectric constant on the electric field applied to the ferroelectric.

Known materials based on Ba _0, 5Sr _0,5 TiO ₃ (O.G. Vendik, Ferroelectrics find their "niche" among the control devices of the microwave. Solid State Physics, 2009, Volume 51, Issue 7, pp. 1441-1445) . They are considered promising for the creation, in particular, of controlled phase shifters of antenna arrays (PAR). To reduce the intrinsic losses of a ferroelectric, it is used in paraphase, i.e. above the Curie point of the material. Acceptable losses of a ferroelectric are realized with a film technology that has not yet been sufficiently developed. To work, such materials require large displacement fields - of the order of 100 kV / cm.

At the same time, there is a need for bulk ferroelectric materials with low losses, operating in the ferroelectric phase in a wide range of operating temperatures and acceptable bias fields - an order of magnitude less than the above value. Known composite ceramic material containing 90 wt.% Crystalline powder of barium titanate, 5 wt.% Barium stannate and 5 wt.% Barium zirconate. This material is made on the basis of available components and has a piezoelectric effect and a sufficiently large dielectric constant of 2300 € (RU 2209192, MPKS04VZ 5/468), publ. July 27, 2003).

 Known ferroelectric composite material for the manufacture of the working fluid of the antenna, containing 78 - 88 wt.% Barium titanate, 5.5 - 10 wt.% Barium zirconate and 6.5 - 12 wt.% Barium stannate (EA008787, MPKS04VZ 5/468, publ. August 31, 2007). This ferroelectric composition makes it possible to obtain a working fluid with an improved signal-to-noise ratio and an increased density of radio channels.

 Known composite material with high dielectric constant and high dielectric strength, which contains ceramic particles with a trimodal distribution, including barium titanate, titanabarium - strontium, or a combination thereof and a polymer binder (US 88897776, MPKS04VZ 5/468, publ. 18.1 1.2014. )

 Known ferroceramic capacitor dielectric with high dielectric constant and low sintering temperature, containing barium titanate 95, 18 - 95.43%, niobium pentoxide 1, 03 - 05%, cobalt oxide 0.22 - 0.24%, manganese dioxide 0.04 - 0.06%, glass fiber 1, 97 - 2.03% and zinc orthosilicate 1, 25 - 1, 50% (RU 2413325, MPKS04V35 / 46, publ. 02.27.201 1 g).

 However, ferroelectric materials known in the art are not suitable for the manufacture of microwave antennas, both due to losses in the microwave region and due to the low residual polarization.

The objective of the claimed invention is the creation of material for antennas in the microwave range. The technical result achieved at the same time consists in obtaining a ferroelectric ceramic material operating in the ferroelectric phase, in a wide temperature range, with low losses and control fields.

The specified technical result is achieved by the fact that ferroelectric ceramics for the manufacture of microwave antennas based on barium titanate (BaTi0 ₃ ) and barium zirconate (BaZr0 ₃ ) includes the addition of bismuth silicate (Bi ₂ Si0 ₅ ) in the following ratio, wt.%: BaT ₃ = 85.5 - 85.7; BaZr0 ₃ = 5.3-5.8; Bi ₂ Si0 ₅ = 8.5 - 9, 1.

The technical result of the invention is provided by introducing into the composition of the material an additive of bismuth silicate Bi ₂ Si0 ₅ in an amount of 8.5 - 9.1% wt.% And changing the content of all the ingredients that make up the material in the specified range.

Since at room temperature the dielectric constant ε of bismuth silicate is small, and the Curie point Т _с is high (ε = 10; Т _с = 610, A. Firsov et al. Crystallography, 1984, vol. 29, p. 509), then an increase in the content of bismuth silicate in the ferroelectric ceramics of barium titanate zirconate will lead to a decrease in its dielectric constant, an increase in thermal stability, and an expansion of the operating temperature range. In this case, however, the concentration of the introduced bismuth silicate additive should be optimized.

 The proposed use of bismuth silicate in an amount of 8.5 - 9.1% wt.% Ensures the achievement of the specified parameters for the value of the dielectric constant and its relative change of not more than ± 20% in the temperature range -60 + 60 ° C, which is a necessary condition for using this ferroelectric ceramic to create microwave antennas.

The proposed bismuth silicate additive is located between the grains ceramics and partially enters the composition of the shell of complex barium titanium zirconate, forming the zonal-clad shell-shaped structure of ceramics.

 The invention is illustrated by illustrations, in which Fig. 1 shows the frequency dependence of the dielectric constant and the loss tangent of a sample of ferroelectric ceramics, measured in the range 100 Hz - 1 GHz, and Fig. Figure 2 shows the ferroelectric hesteresis loops, and Figure 3 shows the temperature dependence of the change in dielectric constant and loss tangent.

 As follows from the data presented, the polarization field of the limit loop is at 12 kV / cm.

The dielectric constant ε of said ferroelectric ceramic varies from 750 to 910 in the range from 210 to 350 K, is practically constant in the temperature range of 260 to 350 ⁰ Kelvin, and reaches 910 units at room temperature.

 Thus, the implementation of the invention will allow to obtain ferroceramic materials for microwave antennas that do not contain hazardous components - lead and strontium oxides, with a relative change in dielectric constant in the temperature range -60 + 60 ° C of not more than ± 20%.

 To obtain this ferroelectric ceramics, standard technology and materials are used. By changing the composition within the specified limits, it is possible to obtain various characteristics depending on the tasks and purpose of the use of the material.

Claims

 CLAIM  Ferroelectric ceramics for the manufacture of microwave antennas based on barium titanate and barium zirconate, including the addition of bismuth silicate, in the following ratio, wt.%: barium titanate 85.5 - 85.7 barium zirconate 5.3 - 5.8 bismus silicate 8.5 - 9, 1