RU2596837C1 - Piezoelectric ceramic material - Google Patents

Abstract

FIELD: construction; electricity.

SUBSTANCE: invention relates to piezoelectric ceramic materials. Piezoelectric ceramic material contains oxides at following ratio of initial components, wt%: PbO 44.17-47.84, SrO 12.67-14.58, BaO 6.98-8.03, TiO₂ 30.55-31.26, SiO₂ 1.96.

EFFECT: high values of relative permittivity, reduced dielectric losses, mechanical q-factor and electromechanical coupling factor of radial oscillation mode.

1 cl, 3 tbl

Description

The invention relates to piezoelectric ceramic materials based on lead titanate and can be used in low-frequency ultrasound transducers, in particular, in medical diagnostic equipment, non-destructive testing devices, etc.

(от 400 до 450).For these applications, the piezoelectric ceramic material must have high values of the electromechanical coupling coefficient of the thick vibration mode, K _t (more than 0.40), piezoelectric coefficient, d ₃₃ (more than 40), mechanical Q factor, Q _M (more than 500), low values of the dielectric loss tangent , tgδ (less than 1.0%), radial mode electromechanical coupling coefficient oscillations, K _p (less than 0.10) and low relative permittivity,

(400 to 450).

Lead titanate, PbTiO ₃ , is the main component of most industrially produced piezoceramics, as well as an independent functional material due to its high Curie temperature and anisotropy of properties, low dielectric constant. The disadvantage of lead titanate is the limited variety of properties, self-destruction of ceramics, and the complex technology of manufacturing materials based on it. One of the ways to improve manufacturability and change the properties of lead titanate is modification, including alkaline earth elements [1-3].

, tgδ=0.012-0.020, K_t=0.51-0.59, K_p=0.026-0.039, Q_M=10-30, T_k=270-327°C [4].A known piezoelectric ceramic material based on lead titanate, including PbTiO ₃ , CaTiO ₃ , Pb (W _1/2 Co _1/2 ) O ₃ , Pb (W _1/2 Zn _1/2 ) O ₃ , Pb (BO ₂ ) ₂ , PbMnO ₃ . Material has parameters

, tgδ = 0.012-0.020, K _t = 0.51-0.59, K _p = 0.026-0.039, Q _M = 10-30, T _k = 270-327 ° C [4].

и Q_M, высокие диэлектрические потери (tgδ). Кроме того, недостатком указанного материала является его многокомпонентный состав, что усложняет технологию изготовления. Материал спекается по обычной керамической технологии в атмосфере кислорода.For these applications, the material is low.

and Q _M , high dielectric loss (tanδ). In addition, the disadvantage of this material is its multicomponent composition, which complicates the manufacturing technology. The material is sintered using conventional ceramic technology in an oxygen atmosphere.

, K_t=0.40-0.44, K_p=0.08, Q_M=1260-1660, d₃₃=50-55 пКл/Н, T_k=448-462°С [5].A known piezoelectric ceramic material based on lead titanate, including PbTiO ₃ , La _2/3 TiO ₃ , Pb (W _1/2 Mn _1/2 ) O ₃ . Material has parameters

_{, K t = 0.40-0.44, K p} = 0.08, Q M = 1260-1660, d ₃₃ = 50-55 pC / N, T _k = 448-462 ° C [5].

и высокие значения Q_M. Кроме того, указанный материал изготавливается дорогостоящим методом горячего прессования.For these applications, the material is low.

and high values of Q _M. In addition, the specified material is made by an expensive method of hot pressing.

, tgδ=0.0031-0.0041, K_t=0.46-0.49, d₃₃=74-78 пКл/Н, Q_M=1254-2162, K_p=0.12-0.14, T_k=321-322°С [6].A known piezoelectric ceramic material based on lead titanate is described by the formula Pb _0.88 (La _0.6 Nd _0.4 ) _0.08 (Mn _1/3 Sb _2/3 ) _0.02 Ti _0.98 O ₃ and additionally containing Co ₂ O ₃ from 0.15 to 0.85 wt.%. The material has compositions with parameters:

, tgδ = 0.0031-0.0041, K _t = 0.46-0.49, d ₃₃ = 74-78 pC / N, Q _M = 1254-2162, K _p = 0.12-0.14, T _k = 321-322 ° С [6].

и слишком высокие значения Q_M. Кроме того материал имеет многокомпонентный состав, содержит элементы с переменной валентностью, что усложняет технологический процесс и приводит к неповторяемости параметров материала.For these applications, the material is low.

and too high Q _M values. In addition, the material has a multicomponent composition, contains elements with a variable valency, which complicates the process and leads to the non-repeatability of the material parameters.

, K_t=0.439-0.498, d₃₃=65-70 пКл/Н, Q_M=1237-1937 [7] и принят за прототип. Материал имеет недостаточно высокую величину

и высокие значения Q_M.The closest to the claimed material in technical essence and the achieved result is a piezoelectric ceramic material based on lead titanate, described by the formula Pb _0.76 (Ca _0.24-x Sr _x ) Ti _0.96 (Mn _1/3 Sb _2/3 ) _0.04 O ₃ , 0 < x≤0.05, and containing additives Na ₂ CO ₃ and Li ₂ CO ₃ in an amount of 0.1-0.3 wt.%. The material has the best compositions with the parameters:

, K _t = 0.439-0.498, d ₃₃ = 65-70 pC / N, Q _M = 1237-1937 [7] and taken as a prototype. The material is not high enough

and high values of Q _M.

, снижение диэлектрических потерь tgδ менее 1.0%, механической добротности до Q_M=500-700 и коэффициента электромеханической связи радиальной моды колебаний K_p менее 0.10 при сохранении высоких значений пьезомодуля d₃₃ более 40 пКл/Н и коэффициента электромеханической связи толщиной моды колебаний K_t более 0.40. При этом материал должен быть изготовлен по обычной керамической технологии, допускающей его массовое производство.The technical result of the present invention is to increase the relative permittivity to values

, reduction in dielectric loss tanδ less than 1.0%, mechanical quality factor to Q _M = 500-700 and the coefficient of electromechanical coupling of the radial vibration mode K _p less than 0.10 while maintaining high values of the piezoelectric module d ₃₃ more than 40 pC / N and the coefficient of electromechanical coupling thickness of the mode of vibration K _t more than 0.40. In this case, the material should be manufactured using conventional ceramic technology, allowing its mass production.

The specified technical result is achieved in that the piezoelectric ceramic material containing oxides of PbO, SrO and TiO ₂ according to the invention additionally contains oxides BaO and SiO ₂ in the following ratio of starting components, wt.%:

Pbo 44.17-47.84 Sro 12.67-14.58 Wow 6.98-8.03 TiO ₂ 30.55-31.26 SiO ₂ 1.96

The studies conducted by the authors showed that the introduction of alkaline earth cations into solid solutions based on lead titanate, partially replacing lead in the A sublattice and having lower electronegativity and polarizing effect compared to the lead cation, leads to a decrease in the degree of covalence of AO bonds and, as a result, to reduce spontaneous deformation, to strengthen the “ferroelectric softness” of the material, that is, to increase its dielectric constant. The introduction of silicon oxide, belonging to the group of glass-forming, helps to improve the manufacturability of the inventive piezoceramic material due to the participation of liquid phases in the sintering of the samples.

Table 1 shows the values of the electrophysical parameters of the inventive piezoelectric ceramic material depending on the composition.

Table 2 shows the comparative electrophysical parameters of the prototype and the optimal compositions of the inventive piezoelectric ceramic material.

Oxides and carbonates of the following qualifications were used as starting components: PbO “h” (99.0%), SrCO ₃ “chda” (99.5%), BaCO ₃ “chda” (99.5%), TiO ₂ “ch” (98.0%), SiO ₂ osch (99.9%).

Piezoelectric ceramic material is made according to conventional ceramic technology as follows. The synthesis is carried out by double firing the mixtures at temperatures T ₁ = T ₂ = 950-980 ° C under isothermal Extracts duration τ ₁ = τ ₂ = 4 hours. Sintering samples in the form of columns ⌀12 mm, height of 15-18 mm performed at T _ch = 1200-1260 ° C for an isothermal exposure time of τ = 3 hours. Metallization (deposition of electrodes) is carried out by applying silver-containing pastes previously ground to a thickness of 1 mm to flat surfaces and then annealing them at 800 ° C for 0.5 hours. polarized in polyethylene siloxane Liquids at a temperature of 140 ° C for 40 min in a constant electric field intensity of 2.5-5.0 kV / mm.

, тангенс угла диэлектрических потерь tgδ, пьезомодуль d₃₃, коэффициенты электромеханической связи планарной K_p и толщинной K_t мод колебаний, механическую добротность Q_M. Высокотемпературные диэлектрические спектры измеряли на специальном стенде, сконструированном в НИИ физики ЮФУ, с использованием прецизионных LCR-метров Agilent 4980А. Измерения проводили в интервале температур 25-600°С и в частотном диапазоне от 25 Гц до 1.0 МГц. Глубина дисперсии относительной диэлектрической проницаемости Δε/ε₀ рассчитывалась по известной формуле Δε=[((ε_m25Гц-ε_m1МГц)/ ε_m25Гц)]·100%. Для определения степени поглощения электромагнитных волн СВЧ-диапазона (1.0-9.0 ГГц) образцами заявляемого пьезоматериала использовалась установка на основе анализатора цепей Е8363В 10 Hz - 40 GHz Series PNA Network Analyzer Agilent Technologies (США).In accordance with OST 11 0444-87, the electrophysical characteristics were determined: the relative dielectric constant of polarized samples

, dielectric loss tangent tanδ, piezoelectric module d ₃₃ , electromechanical coupling coefficients of planar K _p and thickness K _t vibration modes, mechanical quality factor Q _M. High-temperature dielectric spectra were measured on a special bench designed at the Research Institute of Physics of Southern Federal University, using Agilent 4980A precision LCR meters. The measurements were carried out in the temperature range of 25-600 ° C and in the frequency range from 25 Hz to 1.0 MHz. The dispersion depth of the relative permittivity Δε / ε _{0 was} calculated using the well-known formula Δε = [((ε _m25Hz- ε _{m1 MHz} ) / ε _{m25 Hz} )] · 100%. To determine the degree of absorption of electromagnetic waves in the microwave range (1.0-9.0 GHz) by the samples of the inventive piezoelectric material, a setup based on the E8363B 10 Hz - 40 GHz Series PNA Network Analyzer Agilent Technologies (USA) was used.

, tgδ=0.0050-0.0061, K_t=0.48-0.50, d₃₃=45-50 пКл/Н, K_p=0.08-0.10, Q_M=590-670. Выход за пределы заявленных концентраций компонентов (примеры 1, 5) приводит к снижению целевых параметров, в частности

, K_t и d₃₃.As follows from table 1, examples 2-4 indicate that the inventive piezoelectric ceramic material has a combination of electrophysical parameters that meet the objective of the invention:

, tgδ = 0.0050-0.0061, K _t = 0.48-0.50, d ₃₃ = 45-50 pC / N, K _p = 0.08-0.10, Q _M = 590-670. Going beyond the declared concentrations of the components (examples 1, 5) leads to a decrease in target parameters, in particular

, K _t and d ₃₃ .

до значений 405-449, снижение Q_M до 590-670 и tgδ до 0.0052-0.0061 при сохранении высоких значений K_t=0.49-0.50 и d₃₃=47-50 пКл/Н. Состав предлагаемого материала отличается простотой (малокомпонентностью), что упрощает технологию его изготовления и позволит использовать в массовом производстве. Следует отметить также и другие преимущества предлагаемого пьезокерамического материала, а именно повышенную стабильность параметров, что подтверждается исследованиями дисперсии диэлектрической проницаемости (глубина дисперсии минимальна в этой области (таблица 1, примеры 3, 4) и составляет Δε=9.7-21.8% в интервале рабочих температур), и высокие значения параметра, характеризующего степень поглощения электромагнитных волн СВЧ-диапазона образцами заявляемого пьезоматериала |S₂₁|=(41-43) дБ (1.0-9.0 ГГц) (таблица 1, примеры 2, 4).The data shown in table 2, confirm the advantages of the proposed piezoelectric ceramic material compared with the material of the prototype, namely the increase

to values 405-449, a decrease in Q _M to 590-670 and tanδ to 0.0052-0.0061 while maintaining high values of K _t = 0.49-0.50 and d ₃₃ = 47-50 pC / N. The composition of the proposed material is simple (low component), which simplifies the technology of its manufacture and will allow use in mass production. It should also be noted other advantages of the proposed piezoceramic material, namely increased stability of the parameters, which is confirmed by studies of the dispersion of the dielectric constant (the dispersion depth is minimal in this area (table 1, examples 3, 4) and amounts to Δε = 9.7-21.8% in the range of operating temperatures ), and high values of the parameter characterizing the degree of absorption of electromagnetic waves of the microwave range by the samples of the inventive piezomaterial | S ₂₁ | = (41-43) dB (1.0-9.0 GHz) (table 1, examples 2, 4).

, высокие значения K_t=0.49-0.50 и d₃₃=47-50 пКл/Н заявляемого пьезоматериала определяют основное его назначение - использование в различных ультразвуковых преобразователях, работающих в частотном диапазоне 7.1-8.0 МГц (таблица 3), в частности, в устройствах медицинской диагностики; низкие значения диэлектрических потерь позволяют увеличить КПД преобразователя, который пропорционален величине

; высокая анизотропия пьезоэлектрических параметров K_t/K_p=5.4÷6.2 способствует подавлению нежелательных колебаний, улучшает отношение сигнал/шум. Указанные выше дополнительные преимущества заявляемого пьезоэлектрического материала позволяют использовать его в высокостабильных ультразвуковых преобразователях, а также при разработке защитных покрытий для медицинских приборов и персонала, работающего с источниками СВЧ-излучения; в СВЧ-антеннах различного назначения, поглотителях паразитных видов колебаний, согласующих нагрузках.Values

high values of K _t = 0.49-0.50 and d ₃₃ = 47-50 pC / N of the inventive piezoelectric material determine its main purpose - use in various ultrasonic transducers operating in the frequency range 7.1-8.0 MHz (table 3), in particular, in devices medical diagnostics; low values of dielectric losses can increase the efficiency of the converter, which is proportional to

; high anisotropy of the piezoelectric parameters K _t / K _p = 5.4 ÷ 6.2 helps to suppress unwanted vibrations, improves the signal-to-noise ratio. The above additional advantages of the claimed piezoelectric material allow it to be used in highly stable ultrasonic transducers, as well as in the development of protective coatings for medical devices and personnel working with microwave sources; in microwave antennas for various purposes, absorbers of spurious oscillations, matching loads.

, где k - коэффициент, зависящий от размеров элементов, ε₀=8.85·10^-12 Ф - диэлектрическая проницаемость вакуума; при k=1

.The possibility of using the inventive piezomaterial in the specified frequency range is confirmed by the following calculations. Provided the converter is matched with the load R _i = R _n , the output resistance R _{n, which} is usually implemented in commercial electronic equipment, is of the order of 50 Ohms for high frequencies using the formula for the capacitance of the converter R _i = 1 / ωС, where R _i is the capacitance of the converter Ohm; ω is the circular frequency, Hz; C is the capacity, f; - it is possible to estimate intervals capacitance C = 1 / 2πfR _i values for these frequency bands and consequently also the relative permittivity polarized elements,

where k is a coefficient depending on the size of the elements, ε ₀ = 8.85 · 10 ^-12 F is the dielectric constant of the vacuum; for k = 1

.

, включая заявляемый материал и прототип, реализуемые на объемных керамических образцах. Таким образом, для работы ультразвуковых преобразователей в диапазоне частот менее 10 МГц необходимы значения

, что соответствует параметрам заявляемого материала.Table 3 shows the frequency ranges for different values

, including the claimed material and prototype, implemented on bulk ceramic samples. Thus, for the operation of ultrasonic transducers in the frequency range less than 10 MHz, values are necessary

that corresponds to the parameters of the claimed material.

Information sources

1. Duran P., Fdez Lozano J.F., Capel F., Moure C. Large electromechanical anisotropic modified lead titanate ceramics // J. Mater. Science. 1989. V. 24. P. 447-452.

2. Chu S.-Y., Chen C.-H. Effect of calcium on the piezoelectric and dielectric properties of Sm-modified PbTiO ₃ ceramics // Sensor and Actuators A. 2001. V. 89. P. 210-214.

3. Chen T.-Y., Chu S.-Y. The piezoelectric and dielectric properties of Ca-additive Sm-modified PbTiO ₃ ceramics intended for surface acoustic wave devices // J. Eur. Ceram. Soc. 2003. V. 23. P. 2171-2176.

4. SU 1634655, IPC C04B 35/00, publ. 03/15/1991. Bull. No. 10.

5. SU 1135736, IPC C04B 35/00, publ. 01/23/1985. Bull. Number 3.

6. CN 101717251 (A), IPC С04В 35/472. Modified lead titanate piezoelectric ceramic material and preparation method thereof, publ. 06/02/2010.

7. KR 10-0765176 (B1), IPC C04B 35/472. Piezoelectric ceramics and the manufacturing method thereof, publ. 10/02/2007 - a prototype.

Claims (1)

Piezoelectric ceramic material containing oxides of PbO, SrO and TiO ₂ , characterized in that it additionally contains oxides of BaO and SiO ₂ in the following ratio of starting components, wt.%:
Pbo 44.17-47.84 Sro 12.67-14.58 Wow 6.98-8.03 TiO ₂ 30.55-31.26 SiO ₂ 1.96