RU2358953C2 - Piezoelectric ceramic material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention can be used in devices for defectoscopy of equipment of atomic reactors, working at high temperatures. The piezoelectric ceramic material based on lithium metaniobate contains oxides of lithium, niobium and strontium at the following ratio of components, wt %: Li₂O - 9.02÷9.17; Nb₂O₅ - 86.27÷86.77; SrO - 4.71÷4.06. The material is made using traditional ceramic processing technology.

EFFECT: attaining upper limit of working temperature, electromechanical coupling coefficient of the width of oscillation mode, piezoelectric modulus; ratio of electromechanical coupling coefficient of the width and planar oscillation mode and piezoelectric modulus approach infinity, which enables suppression of parasitic oscillations, distorting the operational signal.

2 ex, 2 tbl

Description

The invention relates to piezoelectric ceramic materials based on lithium methaniobate and can be used in inspection devices of equipment of nuclear reactors operating at high temperatures.

The closest to the claimed material in technical essence and the achieved result is a piezoelectric ceramic material based on lithium methaniobate, including Li ₂ O, Nb ₂ O ₅ , B ₂ O ₃ , SiO ₂ , CaO. The material has an upper working temperature limit T _slave = (900 + 1220) K, the piezoelectric module d ₃₃ = (6.9 + 13.0) pC / N, the electromechanical coupling coefficient of the thickness vibration mode k _t = 0.20, the final (and low ) the ratio of electromechanical coupling coefficients of thickness k _t and planar k _p vibration modes k _t / k _p = 20, the ratio of piezoelectric modules d ₃₃ / | d ₃₁ = 20 (low anisotropy of piezoelectric properties). (Smotrakov V.G., Panich A.E., Polonskaya AM, Eremkin V.V., Vusevker Yu.A. Piezoceramic material. // RF Patent No. 2040506 of 07.25.1995 on Application No. 5058742/33 (priority of 14.08 .1992), IPC С04В 35/00) (prototype). For the indicated application, the material has insufficiently high T _slave , k _t , d ₃₃ , k _t / k _p , d ₃₃ / | d ₃₁ |.

The objective of the invention is to obtain the values of T _slave = 1400 K, k _t = 0.32 ÷ 0.35, d ₃₃ = 18-20 pC / N, k _t / k _p = d ₃₃ / | d ₃₁ | → ∞.

This result is achieved in that the piezoelectric ceramic material based on lithium methaniobate, including Li ₂ O, Nb ₂ O ₅ and additives, contains SrO as an additive in the following ratio of components, wt.%: Li ₂ O - 9.02 ÷ 9, 17; Nb ₂ O ₅ - 86.27 ÷ 86.77; SrO - 4.71 ÷ 4.06.

Oxides and carbonates of the following qualifications were used as initial components: Li ₂ CO ₃ - “hch”, Nb ₂ O ₅ - “Nbo-Fri”, SrO - “chda”.

1. An example of the manufacture of a piezoelectric material

The material is manufactured by conventional ceramic technology as follows. The synthesis is carried out by double firing a mixture of Li ₂ O 9,02 wt.%,

,

, длительности изотермических выдержек τ₁=τ₂=14,4·10³ с. Спекание образцов диаметром 12÷15 мм, высотой 3-5 мм осуществляется двукратными обжигами, при этом первый обжиг при

производят под давлением 10 МПа в течение 0,3·10³ с, а второй - без давления при Т_сп.2 1300 К в течение 7,2·10³ с. Металлизация (нанесение электродов) производится путем нанесения на плоские поверхности предварительно сошлифованных до толщины 1 мм образцов серебросодержащей пасты и последующего ее вжигания при температуре Т_вжиг=1070 К в течение 1,8·10³ с. Образцы поляризуют в полиэтиленсилоксановой жидкости при температуре 450 К в течение 2,4·10³ с в постоянном электрическом поле напряженностью 70 кВ/см.Nb ₂ O ₅ 86.27 wt.%, SrO 4.71 wt.%, With intermediate grinding of the synthesized product. Firing temperatures

,

, the duration of isothermal exposure τ ₁ = τ ₂ = 14,4 · 10 ³ s Sintering of samples with a diameter of 12 ÷ 15 mm, a height of 3-5 mm is carried out by double firing, with the first firing at

produced under a pressure of 10 MPa for 0.3 · 10 ³ s, and the second without pressure at T _{SP 2} 1300 K for 7.2 · 10 ³ s. Metallization (deposition of electrodes) is carried out by applying silver-containing paste samples previously ground to a thickness of 1 mm to flat surfaces and annealing them at a temperature T _annealing = 1070 K for 1.8 · 10 ³ s. Samples are polarized in a polyethylene siloxane liquid at a temperature of 450 K for 2.4 · 10 ³ s in a constant electric field with an intensity of 70 kV / cm.

The electrophysical characteristics are determined in accordance with OST 11.0444-87, the piezoelectric module d _{33 is} measured by a quasistatic method.

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

производят под давлением 10 МПа в течение 0,3·10³ с, а второй - без давления при

в течение 7,2·10³ с. Металлизация (нанесение электродов) производится путем нанесения на плоские поверхности предварительно сошлифованных до толщины 1 мм образцов серебросодержащей пасты и последующего ее вжигания при температуре Т_вжиг=1070 К в течение 1,8·10³ с. Образцы поляризуют в полиэтиленсилоксановой жидкости при температуре 450 К в течение 2,4·10³ с в постоянном электрическом поле напряженностью 70 кВ/см.The material is manufactured by conventional ceramic technology as follows. The synthesis is carried out by double firing a mixture of Li ₂ O 9.17 wt.%, Nb ₂ O ₅ 86.77 wt.%, SrO 4.06 wt.% With intermediate grinding of the synthesized product. Firing temperatures T _{synth. 11} 1120 K, T _{synth. 2} 1170 K, isothermal exposure durations τ ₁ = τ ₂ = 14.4 · 10 ³ s. Sintering of samples with a diameter of 12-15 mm, a height of 3-5 mm is carried out by double firing, with the first firing at

produced under a pressure of 10 MPa for 0.3 · 10 ³ s, and the second without pressure at

within 7.2 · 10 ³ s. Metallization (deposition of electrodes) is carried out by applying silver-containing paste samples previously ground to a thickness of 1 mm to flat surfaces and annealing them at a temperature T _annealing = 1070 K for 1.8 · 10 ³ s. Samples are polarized in a polyethylene siloxane liquid at a temperature of 450 K for 2.4 · 10 ³ s in a constant electric field with an intensity of 70 kV / cm.

The electrophysical characteristics are determined in accordance with OST 11.0444-87, the piezoelectric module d _{33 is} measured by a quasistatic method.

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 for the optimal composition of the proposed material.

The obtained experimental data (Fig. 1, Table 1, examples 4, 5) indicate that the piezoelectric ceramic material of the proposed composition has optimal characteristics from the point of view of the technical problem to be solved in the indicated range of component values.

The data shown in figure 2 (table 2), confirm the advantages of the proposed piezoelectric ceramic material compared with the material of the prototype, namely the increase in the upper limit of the operating temperature T _slave. up to 1400 K, piezoelectric module ratios d ₃₃ / | d ₃₁ | and electromechanical coupling coefficients of the thickness and planar vibration modes k _t / k _p to infinity due to the "reduction" to zero | d ₃₁ | and k _p , increasing the values of the piezoelectric characteristics d ₃₃ and k _t . The mechanical quality factor Q _{m of the} material is less than 100, the relative dielectric constant is ε ₃₃ ^t / ε _о ~ 50, and the dielectric loss is <2% (tanδ · 10 ² = 1.9). The expansion of the ranges of concentrations of the constituent components (examples 1, 2, 3, 6, 7 of Table 1.) leads to a decrease in T _slave , d ₃₃ / | d ₃₁ |, k _t / k _p , d ₃₃ , k _t .

, слоистую кристаллическую структуру и ориентированную (текстурированную) зеренную структуру, наследуемые предлагаемым материалом. Благоприятствует повышению указанных параметров и использование на стадии рекристаллизации (образования зеренной структуры) при

кратковременного воздействия извне приложенного давления («ковка»), способствующего текстурированию материала и, как следствие, усилению пьезоотклика.The effect of improving these parameters is achieved substantially by introducing a lithium metaniobate (LiNbO ₃₎ pironiobata strontium (Sr ₂ Nb ₂ O ₇₎ having a higher than the LiNbO _3, the Curie temperature

, a layered crystalline structure and oriented (textured) grain structure, inherited by the proposed material. The use at the stage of recrystallization (formation of a grain structure) at

short-term exposure from outside the applied pressure (“forging”), which contributes to the texturing of the material and, as a result, to enhance the piezoelectric response.

The proposed piezoelectric ceramic material is obtained by conventional ceramic technology without the use of glass-forming additives (B ₂ O ₃ , SiO ₂ ) used in the prototype, which significantly complicate the process (due to their crystal-chemical features). In addition, the use of toxic boron compounds sharply limits the range of possible applications of piezoceramics (Directive 2002/95 / EC of the European Parliament as revised on January 27, 2003 on the use of hazardous materials in electronics and electronic devices). In our case, the simple chemical composition of the proposed material, which does not contain volatile toxic substances, allows us to simplify and cheapen the process of manufacturing piezoceramic products.

The indicated parameters of the new material will allow it to be used in a wider temperature range, and the infinite anisotropy of the piezoelectric properties combined with low mechanical Q factor Q _m will lead to an increase in the signal-to-noise ratio and suppression of spurious resonances (false oscillations), which distort the shape of the working signal and worsen the characteristics made of these sensor materials. This is conducive to increasing the resolution and sensitivity of materials and sensors. The achievement of infinite anisotropy of the piezoelectric properties is not associated with the development of microcracks in ceramics, as is the case in other high-temperature materials with high ratios k _t / k _p and d ₃₃ / | d ₃₁ |. This is a consequence of the qualitatively-quantitative elemental composition of the proposed material and the features of its crystalline and grain structures. The low relative permittivity ε ₃₃ ^t / ε _о and the dielectric loss tangent tanδ of the material allow it to be used in microwave technology, and the low specific gravity d is used in devices where weight characteristics are decisive.

Claims (1)

A piezoelectric ceramic material based on lithium methaniobate, including Li ₂ O and Nb ₂ O ₅ , characterized in that it additionally contains SrO in the following ratio of components, wt.%:
Li ₂ O 9.02 ÷ 9.17 Nb ₂ O ₅ 86.27 ÷ 86.77 Sro 4.71 ÷ 4.06

Images