RU2498959C2 - Piezoelectric ceramic material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of piezoelectric ceramic materials and can be used in making high-frequency electromechanical transducers particularly used in ultrasonic delay lines (used in the 20-30 MHz range), highly sensitive single-response crystals operating on thickness vibrations; in devices where weight characteristics are decisive. The piezoelectric ceramic material based on sodium niobate contains sodium, niobium, lithium, strontium, aluminium and manganese oxides, with the following ratio of components, wt %: Na₂O 16.28-16.50, Nb₂O₅ 79.61-80.71, Li₂O 1.12-1.14, SrO 0.63-0.64, Al₂O₃ 0.31-0.32, MnO₂ 0.69-2.05. The material is produced using conventional ceramic processing. The firing temperature during synthesis is equal to 1133 K.

EFFECT: material has low relative permittivity of polarised samples, high piezoelectric sensitivity on the thickness vibration mode, sufficiently high mechanical Q-factor, as well as high sound speed, low density and high piezo-anisotropy.

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Description

The invention relates to piezoelectric ceramic materials based on sodium niobate and can be used to create high-frequency electromechanical transducers, in particular, used in ultrasonic delay lines (operated in the frequency range (20 ÷ 30) MHz), high-sensitivity mono-frequency resonators operating in thickness vibrations.

For these applications, the material should have low values of relative permittivity of polarized samples, ε ₃₃ ^T / ε ₀ , (100 ÷ 150), high piezoelectric sensitivity, g ₃₃ , (≈40 mV · m / N) at a thick vibration mode, a sufficiently high mechanical quality factor, Q _m , (500 ÷ 1500).

Known piezoelectric material based on sodium niobate, including Na ₂ O, K ₂ O, Nb ₂ O ₅ and oxide compounds of divalent and trivalent elements (Fe, Co, Ni, Mg, Zn, Cu). The material has ε ₃₃ ^T / ε ₀ = (250 ÷ 1343), g ₃₃ = (13.5 ÷ 38.3) mV · m / N (Patent EP 1630149 (A1) Published 01.03.2006. Authors: Masato Yamazaki, Kohei Ito, Katsuya Yamagiwa et al .; application No. JP 2003153426, priority dated May 29, 2004. C04B 35/495, C04B 35/499, H01L 41/187). For these applications, the material has a low enough value of ε ₃₃ ^T / ε ₀ and a low enough value of g ₃₃ .

Known piezoelectric ceramic material based on sodium niobate, including Na ₂ O, K ₂ O, Li ₂ O, Nb ₂ O ₅ , Ta ₂ O ₅ , Bi ₂ O ₃ , as well as oxides of two-, three- and tetravalent elements (Ca , Sr, Ba, Ti, Zr, Sn, Sc, Yb, Nd, Sm, etc.). The material has ε ₃₃ ^T / ε ₀ = (765 ÷ 856), g ₃₃ = (32.6 ÷ 36.1) mVm / N (Patent EP 1876155 (A1) Publ. 09.01.2008. Authors: Shimchiro Kawada, Ryoko Katayama, Katsuhiro Horikawa; by application No. JP 2005133255, priority dated April 28, 2005. C04B 35/00, H01L 41/187). For these applications, the material has not sufficiently low values of ε ₃₃ ^T / ε ₀ and not sufficiently high values of g ₃₃ .

Known piezoelectric ceramic material based on sodium niobate, including Na ₂ O, K ₂ O, Li ₂ O, Nb ₂ O ₅ , Ta ₂ O ₅ and oxides CuO and MnO ₂ . The material has ε ₃₃ ^T / ε ₀ ≈1630, g ₃₃ ≈22.2 mVm / N (Patent EP 2113952 (A2) Published 04.11.2009. Authors: Masahito Fumkawa, Takeo Tsukada, Daisuke Tanaka and others; by application No. JP 2008090331 , priority dated March 31, 2008. H01L 41/08, С04В 35/495, H01L 41/187). For these applications, the material has not sufficiently low values of ε ₃₃ ^T / ε ₀ and not sufficiently high values of g ₃₃ .

Closest to the claimed material but technical essence and the achieved result is a piezoelectric ceramic material based on sodium niobate, including Na ₂ O, K ₂ O, Nb ₂ O ₅ , CuO. The composition of the material corresponds to the chemical formula 0.99 (K _0.5 Na _0.5 NbO ₃ ) + 0.01CuO. The material has for the best compositions ε ₃₃ ^T / ε ₀ ≈237, g ₃₃ ≈46.1 mV · m / N, Q _m = 1408 (Patent EP 1032057 (A1). Publ. 30.08.2000. Author: Yasuyoshi Saito; according to applications No. JP 2000042095, priority 02/21/2000) (Prototype). For these applications, the material is not sufficiently low ε ₃₃ ^T / ε ₀ .

The objective of the invention is to reduce ε ₃₃ ^T / ε ₀ (to values of 120 ÷ 140) while maintaining high g ₃₃ values (~ 40 mVm / N) and sufficiently high Q _m (~ 500).

These results are achieved in that the piezoelectric ceramic material based on sodium niobate, including Na ₂ O and Nb ₂ O ₅ , additionally contains Li ₂ O, SrO, Al ₂ O ₃ and MnO ₃ in the following ratio of components, wt.%:

Na ₂ O = 16.28 ÷ 16.50 Nb ₂ O ₅ = 79.61 ÷ 80.71 Li ₂ O = 1.12 ÷ 1.14 SrO = 0.63 ÷ 0.64 Al ₂ O ₃ = 0.31 ÷ 0.32 MnO ₂ = 0.69 ÷ 2.05

The composition of the material corresponds to the formula:

Li _0.86625 Na _0.12375 Sr _0.01 Nb _0.988 Al _0.01 O ₃ + zMnO ₂ , where 0.01≤z≤0.03.

1. An example of the manufacture of a piezoelectric ceramic material.

The material was manufactured by conventional ceramic technology as follows. Hydrocarbonates, carbonates and oxides of the following qualifications were used as initial reagents: NaHCO ₃ - “chda”, Nb ₂ O ₅ - “NbO-PT”, Li ₂ CO ₃ - “hch”, SrO - “hh”, Al ₂ O ₃ - “h”, MnO ₂ - “h”.

The synthesis was carried out by a single firing of mixtures of raw components: NaHCO ₃ , Nb ₂ O ₅ , Li ₂ CO ₃ , SrO, Al ₂ O ₃ , MnO ₂ taken in quantities (mass%, in the case of NaHCO ₃ , Li ₂ CO ₃ , in in terms of the corresponding oxides): Na ₂ O = 16.50; Nb ₂ O ₅ = 80.72; Li ₂ O = 1.14; SrO = 0.64; Al ₂ O ₃ = 0.31; MnO ₂ = 0.69 with intermediate grinding of the synthesized product. The firing temperature in the synthesis of T _synt. = 1123 K, the duration of isothermal exposure τ _synt = 5 hours. Sintering of the samples in the form of columns Ø12 mm, height (15 ÷ 18) mm was carried out at T _sp. = 1433 K, duration isothermal holding, τ h 2 = _ch. Metallization (applying electrodes) made by coating the flat surface of the pre-ground portion to a thickness of 1 mm samples silver-containing paste and its subsequent brazing at a temperature T _vzhig. = 1070 K for 0.5 h. Samples were polarized in a polyethylene siloxane liquid at a temperature of 400 K for 30 min in a constant electric field of 4 kV / cm.

2. An example of the manufacture of a piezoelectric ceramic material.

The material was manufactured by conventional ceramic technology as follows. Hydrocarbonates, carbonates and oxides of the following qualifications were used as initial reagents: NaHCO ₃ - “chda”, Nb ₂ O ₅ - “NbO-PT”, Li ₂ CO ₃ - “hch”, SrO - “hh”, Al ₂ O ₃ - “h”, MnO ₂ - “h”.

The synthesis was carried out by a single firing of mixtures of raw components: NaHCO ₃ , Nb ₂ O ₅ , Li ₂ CO ₃ , SrO, Al ₂ O ₃ , MnO ₂ taken in quantities (mass%, in the case of NaHCO ₃ , Li ₂ CO ₃ in terms of on the corresponding oxides): Na ₂ O = 16.39; Nb ₂ O ₅ = 80.17; Li ₂ O = 1.13; SrO = 0.63; Al ₂ O ₃ = 0.31; MnO ₂ = 1.37 with intermediate grinding of the synthesized product. The firing temperature during synthesis, T _synt. = 1133 K, the duration of isothermal exposure, τ _synt = 5 hours. Sintering of samples in the form of columns Ø12 mm, height (15 ÷ 18) mm was carried out at T _sp. = 1442 K, duration isothermal holding, τ h 2 = _ch. Metallization (applying electrodes) made by coating the flat surface of the pre-ground portion to a thickness of 1 mm samples silver-containing paste and its subsequent brazing at a temperature T _vzhig. = 1070 K for 0.5 h. Samples were polarized in a polyethylene siloxane liquid at a temperature of 400 K for 30 min in a constant electric field of 4 kV / cm.

3. An example of the manufacture of a piezoelectric ceramic material.

The material was manufactured using conventional ceramic technology as follows. Hydrocarbonates, carbonates and oxides of the following qualifications were used as initial reagents: NaHCO ₃ - “chda”, Nb ₂ O ₅ - “NbO-PT”, Li ₂ CO ₃ - “hch”, SrO - “hh”, Al ₂ O ₃ - “h”, MnO ₂ - “h”.

The synthesis was carried out by a single firing of mixtures of raw components: NaHCO ₃ , Nb ₂ O ₅ , Li ₂ CO ₃ , SrO, Al ₂ O ₃ , MnO ₂ taken in quantities (mass%, in the case of NaHCO ₃ , Li ₂ CO ₃ in terms of to the corresponding oxides): Na ₂ O = 16.28; Nb ₂ O ₅ = 79.61; Li ₂ O = 1.12; SrO = 0.63; Al ₂ O ₃ = 0.31; MnO ₂ = 2.05 with intermediate grinding of the synthesized product.

The firing temperature during synthesis, T _synt. = 1133 K, the duration of the isothermal exposure τ _synt = 5 hours. Sintering of the samples in the form of columns Ø12 mm, height (15 ÷ 18) mm was carried out at T _sp. = 1445 K, duration isothermal holding, τ h 2 = _ch. Metallization (applying electrodes) is produced by coating the flat surface of the pre-ground portion to a thickness of 1 mm samples silver-containing paste and its subsequent brazing at a temperature T _vzhig. = 1070 K for 0.5 h. Samples were polarized in a polyethylene siloxane liquid at a temperature of 400 K for 30 min in a constant electric field of 4 kV / cm.

Electrical characteristics were determined in accordance with OST 11.0444-87. The relative permittivities of polarized samples were measured, ε ₃₃ ^T / ε ₀ (ε ₀ is the dielectric constant) of the samples, piezoelectric modules, | d ₃₁ | and d ₃₃ , the electromechanical coupling coefficient of the planar oscillation mode, K _p , mechanical quality factor, Q _m , sound speed, V ₁ ^E. Piezomodule d _{33 was} determined by the quasistatic method. The experimental density of the samples, ρ _exp, was measured by hydrostatic weighing in octane. The piezosensitivity in the thick mode of vibration, g ₃₃ , was calculated by the formula g ₃₃ = d ₃₃ / ε ₃₃ ^T. The acoustic impedance, Z _{a, was} calculated by the formula Z _a = ρ _exp. V ₁ ^E.

Figure 1, where table 1 is shown, shows the main characteristics of the material depending on the composition, and figure 2, which shows table 2, shows the main electrophysical characteristics of the optimal compositions of the proposed material.

The obtained experimental data (Fig. 1, table 1, examples Nos. 3-5) indicate that the piezoelectric ceramic material of the proposed composition has optimal, from the point of view of the technical problem being solved, characteristics in the indicated range of concentrations.

Thus, the positive effect of the proposed material is due to its qualitative and quantitative composition, which is also confirmed by examples No. 1, 2, 6, 7, demonstrating the deterioration of properties outside the proposed range of concentrations of the components. Violation of these limits leads, as can be seen from table 1, to an increase in ε ₃₃ ^T / ε ₀ and a decrease in d ₃₃ and g ₃₃ .

The proposed piezoelectric ceramic material is obtained by conventional ceramic technology, easily adaptable to industrial conditions, without the use of the expensive hot pressing method, often used for the manufacture of such high-frequency materials (1. Danziger A.Ya., Razumovskaya ON, Reznichenko L.A. , Dudkina SI Highly effective piezoceramic materials. Search optimization. Rostov-on-Don: Publishing house Pike. 1995. - 94 p.). This greatly simplifies and reduces the cost of the process.

The data shown in figure 1, 2 (table 1, 2) confirm the advantages of the proposed piezoelectric ceramic material compared with the prototype material, namely, the reduction of ε ₃₃ ^T / ε _{0 is} almost doubled to values (121 ÷ 135), while maintaining a high piezoelectric sensitivity g ₃₃ = (42.0 ÷ 42.6) mVm / N in the thickness mode of vibration and sufficiently high values of mechanical Q factor, Q _m (516 ÷ 558).

The effect of reducing ε ₃₃ ^T / ε _{0 is} achieved essentially by the additional introduction of Li ₂ O, SrO, Al ₂ O ₃ and MnO ₂ .

All of these material parameters allow it to be used in a higher frequency range than the frequency interval in which the described analogues and prototype can be used.

This follows, first of all, from the fact that solid solutions based on alkali metal niobates (NLM) can be used as resonant elements of piezoelectric transducers in high-frequency (HF) (3.0 ÷ 30.0) MHz and very high-frequency (VHF) (30.0 ÷ 300.0) MHz ranges, mid-frequency (MF) (0.3 ÷ 3.0) MHz range; low-frequency (LF) (30.0 ÷ 300.0) kHz and ultra-low-frequency (VLF) (<30.0 kHz) ranges. Classification of electromagnetic waves by frequency ranges is presented in (2. Nosov Yu.N., Kukaev A.A. Encyclopedia of domestic antennas. Reference publication. M. 2001. P.49).

Provided that the converter is matched to the load (R _i = R _n ) (usually the output impedance R _n ~ 50 Ohms for high and medium frequencies and 1000 Ohms for low frequencies commonly used in commercial electronic equipment), 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; - you can approximately estimate the intervals of the capacitance values C = 1 / 2πfR _i for the indicated frequency ranges, and, therefore, the relative dielectric constant of polarized elements, ε ₃₃ ^T / ε ₀ = k · C, where k is a coefficient depending on the sizes of the elements, ε ₀ = 8.85 · 10 ^-12 F is the dielectric constant of the vacuum; at k = 1, ε ₃₃ ^T / ε ₀ = С.

Figure 3-5, which shows tables 3-5, shows the values of the relative dielectric constant, ε ₃₃ ^T / ε ₀ , implemented in bulk ceramic samples in different frequency ranges. There (*) are comments on the tables.

The developed piezoelectric ceramic material can be used to create high-frequency electromechanical transducers, used, in particular, in ultrasonic delay lines (operated in the frequency range 20–30 MHz), highly sensitive mono-frequency resonators operating on thick vibrations.

Besides the aforementioned low values ε ₃₃ ^T / ε _{0, 33} g of high and sufficiently high Q _m, the material is:

- high speed of sound (V ₁ ^E ≈5.8 km / s), which allows to obtain a given frequency on less thin plates. This simplifies the manufacturing technology of RF devices due to the possibility of increasing their resonant sizes (this, in turn, is beneficial from the point of view of reducing the capacity of the converter);

- low density (ρ _exp ≈4.5 g / cm ³ ), which leads, on the one hand, to a significant reduction in the weight of products, and on the other, to a decrease in acoustic impedance (Z _a = ρ _exp V ₁ ^E = 22.8 ÷ 25.7 mrayl) required to match the acoustic load;

- high anisotropy of the piezoelectric properties (d ₃₃ / | d ₃₁ | ~ 4 ÷ 5), which allows to improve the signal-to-noise ratio and simplify the technology, excluding the operation of cutting the material into subelements;

- sufficiently high Curie temperatures, T _k (620 ÷ 640 K) of the material allow it to be used in a wide temperature range.

From the foregoing, it follows that the technical result of the invention is achieved by a new set of essential features both newly introduced and known, therefore, the claimed piezoelectric ceramic material meets the patentability criterion of "inventive step".

The proposed piezoelectric ceramic material provides a technical result, does not cause difficulties in manufacturing, involves the use of basic (affordable and cheap) materials (reagents) and standard equipment, which indicates that the claimed technical solution meets the patentability criterion of "industrial applicability".

Claims (1)

Piezoelectric ceramic material based on sodium niobate, including Na ₂ O and Nb ₂ O ₅ , characterized in that it further contains Li ₂ O, SrO, Al ₂ O ₃ and MnO ₂ in the following ratio of components, wt.%:
Na ₂ O 16.28 ÷ 16.50 Nb ₂ O ₅ 79.61 ÷ 80.71 Li ₂ O 1.12 ÷ 14 Al ₂ O ₃ 0.31 ÷ 0.32 MnO ₂ 0.69 ÷ 2.05 Sro 0.63 ÷ 0.64

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