JP5933335B2 - Piezoelectric material and method for manufacturing piezoelectric material - Google Patents

Description

  The present invention relates to a piezoelectric material, and more specifically, to an improved technique for a piezoelectric material not containing lead.

As a piezoelectric material, PZT (PbTiO ₃ —PbZrO ₃ ) composition ceramics are well known. PZT is excellent in piezoelectric characteristics such as an electromechanical coupling coefficient and a piezoelectric constant, and this PZT is widely used for piezoelectric elements such as sensors, ultrasonic motors, and filters.

  By the way, in recent years, there is an urgent need to make industrial products “lead-free” due to environmental demands. Naturally, since PZT is finally used for industrial products, it is necessary to replace the piezoelectric material from PZT containing lead (Pb) with another piezoelectric material not containing lead.

Then, as the piezoelectric material not containing lead (lead-free piezoelectric material), the general formula _K x _{Na (1-x)} compounds represented by NbO ₃ (KNN), barium titanate _(Ba n TiO ₃₎ based piezoelectric of There are materials. Note that a piezoelectric material containing KNN as a main component (hereinafter referred to as a KNN-based piezoelectric material) is described in Patent Document 1 below, for example. Further, general techniques relating to piezoelectric materials are described in detail in Non-Patent Documents 1 and 2 below.

Japanese Patent Publication No.56-12031

FDK Corporation, “Piezoelectric Ceramics (Technical Document)”, [online], [Search April 6, 2012], Internet <URL: http://www.fdk.co.jp/cyber-j/pdf/ BZ-TEJ001.pdf> NEC TOKIN Corporation, “Piezoelectric Ceramics Vol.04”, [online], [Search April 6, 2012], Internet <URL: http://www.nec-tokin.com/product/piezodevice1/pdf/ piezodevice_j.pdf>

Some inventors related to the present invention (hereinafter, the present inventor) have previously described the general formula {(K _1-a Na _a ) _1-b Li _b } (Nb _1-c-d Ta _c Sb _d ) O The moisture resistance performance of the compound represented by ₃ is examined, and in the course of the study, the composition of each composition constituting the compound (ad in the general formula) is appropriately set and glass is added. Invented a piezoelectric material having improved moisture resistance while maintaining a piezoelectric characteristic that can be used practically, and applied for a patent (Japanese Patent Application No. 2010-57735: Prior Invention No. 1, Japanese Patent Application No. 2010-161856: Prior Invention No. 2) .

  However, in the subsequent research process, in the piezoelectric material containing the above compound as a substance that causes the piezoelectricity, various piezoelectric properties (electromechanical coupling coefficient Kp, relative dielectric constant εr) are all improved. It was found that it was difficult to improve the balance in a balanced manner. That is, in the piezoelectric material composed of the compound alone or the piezoelectric materials according to the first and second inventions, the characteristics of Qm and εr are in a reciprocal relationship. On the extension lines of the first and second inventions, it is extremely difficult to further improve the characteristics of both Qm and εr.

In order to achieve the above object, the present invention provides a piezoelectric material represented by the general formula (K _a Na _b Li _c ) (Nb Bd _e Ta _d Sb _e ) O ₃ + xmol% BaTiO ₃ + ymol% CuO Because
B = 1.1, a + b ≧ 0.96,
0.4 ≦ a ≦ 0.52, 0.46 ≦ b ≦ 0.54, 0.040 ≦ c ≦ 0.057, 0.1 ≦ d ≦ 0.2, 0.005 ≦ e ≦ 0.04, 3 ≦ x <7, 2 ≦ y ≦ 4,
The piezoelectric material is characterized by this.

  The piezoelectric material according to the third aspect of the invention is sufficiently practical when used in a passive piezoelectric device such as a sensor. In addition, depending on conditions, characteristics that can be used for active piezoelectric devices such as buzzers, ultrasonic motors, and bimorphs were also obtained. In subsequent studies, the composition of the piezoelectric material of the prior invention 3 was further optimized, and the characteristics obtained in the prior invention 3 were obtained more stably, and further attempts were made to improve the characteristics. However, the conventional development method of optimizing the composition including the prior invention 3 has a limit in improving the characteristics. Therefore, we decided to fundamentally change the technical idea that is the origin of the development method.

  The present invention was created from the start of changing the technical concept related to the development method of piezoelectric material, and is an environmentally friendly, various piezoelectric characteristics in a well-balanced, active piezoelectric device such as an ultrasonic motor. It is an object to provide an “extraordinarily” excellent piezoelectric material that can be applied to the above. Other purposes will be clarified in the following description.

To achieve the above object, the present invention provides a piezoelectric material represented by the general formula (K _a Na _b Li _c ) (Nb Bd _e Ta _d Sb _e ) O ₃ + xmol% BaTiO ₃ + ymol% CuO. And
B = 1.1, a + b ≧ 0.96,
0.4 ≦ a ≦ 0.52, 0.46 ≦ b ≦ 0.54, 0.004 ≦ c ≦ 0.057, 0.1 ≦ d ≦ 0.2, 0.005 ≦ e ≦ 0.04, 3 ≦ x <7, 2 ≦ y ≦ 4,
The piezoelectric material is characterized by this.

  In addition, in the above piezoelectric material, piezoelectric materials having an electromechanical coupling coefficient Kp, a relative dielectric constant εr, and a mechanical quality factor Qm of Kp ≧ 30%, εr ≧ 900, and Qm ≧ 900 are also included in the scope of the present invention.

The present invention also extends to a method for manufacturing the above piezoelectric material,
A mixing step of mixing a raw material of a compound to be the piezoelectric material and a solvent;
A pre-baking step of baking the mixture of the compound and the solvent at a predetermined temperature lower than a sintering temperature;
A molding step of molding a mixture obtained by adding a binder to the mixture after the preliminary firing step into a predetermined shape;
A firing step of sintering the molded product obtained in the molding step in an oxygen atmosphere;
A method for manufacturing a piezoelectric material characterized by comprising:

  According to the piezoelectric material of the present invention, the environmental load is reduced, various piezoelectric characteristics are well balanced and extremely excellent, and can be widely used in various applications.

It is process drawing for demonstrating the manufacturing method of the piezoelectric material which concerns on the Example of this invention. It is the schematic of the piezoelectric element for evaluating the characteristic of the piezoelectric material which concerns on the Example of this invention.

=== Technical idea of the present invention ===
The destination invention 3 is represented by the general formula _{{(K 1-a Na a} ) 1-b Li b} (Nb 1-c-d Ta c Sb d) O 3 + xmol% Ba n TiO 3 + ymol% CuO In the third aspect of the present invention, by setting the values of x, y, a, b, c, d, and n within an appropriate numerical range, the relative permittivity εr and mechanical properties that have conventionally been in a canceling relationship are set. We succeeded in improving both the quality factor Qm. As described above, the piezoelectric material according to the invention 3 is excellent in various piezoelectric characteristics in a well-balanced manner, and in some applications, it can be replaced with a conventional piezoelectric material containing lead. However, it was not a substitute for all applications. Therefore, the present inventor considered a technique for improving the piezoelectric characteristics. And if the piezoelectric material is a ceramic produced by firing the raw material, and the alkali component that contributes to the piezoelectric properties is volatilized in the course of firing, even if the composition in the above general formula is optimized, I thought it would be difficult to greatly improve the characteristics.

Specifically, in the above general formula representing the piezoelectric material of the invention 3, it is represented by {(K _1−a Na _a ) _1−b Li _b } (Nb _1−c−d Ta _c Sb _d ) O ₃ . (1-a) (1-b) is a, a (1-b) is b, b is c, c is d, and d is e. _b Li _c ) (Nb _1- de Ta _d Sb _e ) O ₃ . The elements constituting the _{(K a Na b Li c)} (Nb 1-d-e Ta d Sb e) O 3 is an alkaline component.

_{Incidentally, (K a Na b Li c} ) In the compound represented by _{(Nb 1-d-e Ta} d Sb e) O 3, (K a Na b Li c) the A _{site, (Nb 1-d-e} Tad _{When d} Sb _e ) is a B site, the compound is a substance having a perovskite crystal structure represented by ABO ₃ with different compositions of A and B. And the ratio of A site and B site is 1: 1. That is, a + b + c = 1 and (1−d−e) + d + e = 1 so that the total ratio of elements constituting each site is 1.

In addition, the ratio of the A site to the B site being 1: 1 as described above is not limited to (K _a Na _b Li _c ) (Nb _1- de Ta _d Sb _e ) O _3, but also piezoelectric. Widely applied to all perovskites in materials. Here, the inventor is on the extension of the previous invention 3, that is, on the assumption that the ratio of the A site to the B site is 1: 1, the values of a to e, x, y, n in the composition It was judged that there was a limit to the improvement of the piezoelectric characteristics only by narrowing down the optimum value.

Next, the present inventor reviewed the ratio of the A site and the B site in the perovskite, that is, the value of a + b + c and the value of B. Volatilized during firing, and in fact it was expected that both a + b + c and B would be less than 1. Then, he came up with the technical idea of compensating for the volatilized alkali component. Of course, if there is an excess or deficiency in the compensation amount, the characteristics may deteriorate instead. In addition, it is easily expected that the characteristics change depending on the ratio with other compositions constituting the piezoelectric material such as BaTiO ₃ and CuO. The present invention has been conceived as a result of intensive studies based on the above technical idea, based on the composition of the piezoelectric material according to the prior invention 3. Hereinafter, the production procedure, composition, and characteristics of the piezoelectric material according to the example of the present invention will be described.

=== Procedure for Manufacturing Piezoelectric Material ===
FIG. 1 shows a procedure for producing a piezoelectric material in an embodiment of the present invention. First, a predetermined amount of raw materials for the piezoelectric material are weighed and blended, and the raw material and an alcohol (such as ethanol) as a solvent are placed in a ball mill and wet mixed (s1). Thereby, the raw material of the piezoelectric material as a sample is mixed and pulverized into powder. Then, the mixture is calcined for 2.5 hours (h) at a temperature of 950 ° C. (s2), the powder after the calcining is wet mixed for 24 h, and the mixture is crushed (s3). Next, an aqueous PVA solution is added as a binder to the crushed mixture and mixed to form a powder with an appropriate particle size (s4). Further, the granulated powder is formed into a desired shape (s5). Here, it was formed into a predetermined shape using a die having a diameter of 21.5 mm and a pressure of about 300 MPa. The molded product is fired in the atmosphere at a temperature of 1000 ° C. to 1100 ° C. for 1 h (s6) to obtain a piezoelectric material that is ceramic.

  Finally, in order to measure the characteristics of the piezoelectric material, it is formed on a piezoelectric element. Specifically, as shown in the side view shown in FIG. 2, the piezoelectric material is processed into a disk shape having a diameter Φ = 17 mm ± 1 mm and a thickness t = 1.0 mm ± 0.05 mm. After the Ag electrodes 3 were baked on both surfaces of the disk-shaped piezoelectric material 2 (s7, s8), the piezoelectric element 1 was obtained by performing a polarization treatment for 30 minutes in a 120 ° C. silicon oil with an electric field of 4 Kv / mm ( s9).

=== About Example of the Invention ===
In the present invention, the subject of the piezoelectric material _{(K a Na b Li c)} (Nb B-d-e Ta d Sb e) as a base material a compound represented by _{O 3,} CuO and Ba _n in this matrix By adding both TiO ₃ as auxiliaries, the technical idea of Prior Invention 3 that complements both disadvantages and comprehensively improves various piezoelectric characteristics is further developed, and an alkali component constituting the base material is added. By adding excessively, it aims to further improve the characteristics.

The piezoelectric material according to an embodiment of the present invention, which is represented by the general formula _{(K a Na b Li c)} (Nb B-d-e Ta d Sb e) O 3 + xmol% Ba n TiO 3 + ymol% CuO is there. Hereinafter, unless otherwise specified, “general formula” refers to this formula. This general formula itself is the same as that defined in the invention 3 as long as a + b + c = A, and A = 1 and B = 1. However, the difference from the prior invention 3 is that, as described above, the A site and the B site are not in a ratio of 1: 1. Then, various piezoelectric materials having different combinations of a to e, x, y, and n in the general formula are prepared as samples, and the piezoelectric characteristics of each sample are evaluated, whereby the specific composition of the piezoelectric material according to the example is determined. Stipulate.

By the way, in the comparative example with respect to the embodiment of the present invention, the so-called “benchmark” piezoelectric material has the most excellent characteristics in the numerical range of a to d, x, y, n defined in the previous invention 3. It becomes. Specifically, it is expressed as (K _0.48 Na _0.48 Li _0.04 ) (Nb _1-0.10-0.04 Ta _0.10 Sb _0.04 ) O ₃ +3 mol% BaTiO ₃ +2 mol% CuO. Piezoelectric material. That is, in the above general formula, a = b = 0.48, c = 0.04, d = 0.10, e = 0.04, B = 1, x = 3, y = 2, and n = 1. Piezoelectric material. Then, various piezoelectric materials based on the above technical idea are manufactured, and piezoelectric materials whose characteristics are improved over the reference sample are examples of the present invention. Here, after defining the composition of Ba _n TiO ₃ in the above general formula to n = 1, which has a track record in the prior invention 3, various samples having different values of a to e and B in the above general formula are prepared, The appropriate values of these values are specified.

=== About Samples ===
The characteristics of the piezoelectric material, particularly the characteristics of the piezoelectric material manufactured by a laboratory-level manufacturing facility, vary greatly from one manufacturing lot to another compared to a manufacturing facility for industrial mass production. That is, even if the reference samples have the same composition, if the production opportunities are different, the characteristics change, and it may not be possible to accurately compare the characteristics with the examples. Therefore, the reference sample was also newly produced at the same time as the other samples by the above-described production procedure, instead of diverting the characteristics obtained in the previous invention 3.

Table 1 below shows the conditions for producing the samples (No. 1 to No. 42).

  In Table 1, no. 1 is a reference sample. No. 2 is No.2. In this sample, the ratio of the B site to 1 is B = 1.1, which is larger than 1.0. That is, by setting the value of B to be greater than 1, an alkali component is naturally excessively added to the B site regardless of the ratio of elements constituting the B site.

No. 3-No. 40 is a sample in which B = 1.1 and the values of a to e, x, and y in the general formula are changed. In addition, No. 1-No. In the 30 samples, the addition amounts of BaTiO ₃ and CuO are the same as those of the reference sample, and x = 3.0 mol% and y = 2.0 mol%. No. The samples Nos. 21, 29, 32, and 37 are No. The sample 17 has the same composition, and “(17)” is added to the column of the sample number so that it can be understood.

  Incidentally, in the reference sample, a + b = 0.96. In the present invention, the purpose is to improve the characteristics by compensating the alkali component volatilized by firing. 2-No. At 40, in order not to satisfy a + b <0.96, the ratio of the other of K or Na at the A site is increased so that a + b ≧ 0.96 is satisfied for the sample having less than 0.48. . Specifically, no. Samples 9, 10, 14, and 15 correspond to this. In the table, a value corresponding to a + b ≧ 0.96 is described in the column a or b corresponding to these samples. Therefore, in the piezoelectric material according to the embodiment of the present invention, one of the conditions is a + b ≧ 0.96.

=== Piezoelectric properties ===
No. 1 shown in Table 1. 1-No. Forty samples, an electromechanical coupling coefficient Kp (%) and a mechanical quality factor Qm (%), which are indicators of piezoelectric characteristics, were measured. Further, the dielectric constant ε ₃₃ ^T was measured, and the relative dielectric constant εr was determined by the equation εr = ε ₃₃ ^T / ε ₀ . The piezoelectric characteristics were measured after the sample produced by the process shown in FIG. 1 was left in the atmosphere for 24 hours.

Table 2 shows the piezoelectric characteristics of the samples (No. 1 to No. 40).

=== About the ratio of B site ===
In Table 2, No. which is a reference sample. When the characteristic of 1 is seen, it is found that Kp = 27.83%, Qm = 594.83, and εr = 757.90, and the characteristics are sufficiently excellent. In contrast, no. No. 2 was obtained by changing the ratio of the B site from 1 to 1.1 (B = 1.1), and the characteristics were improved for all of Kp, Qm, and εr. In particular, the characteristic of εr was greatly improved. Therefore, it was confirmed that the B site ratio was 1.1. Therefore, sample no. 3-No. 40 defines B = 1.1, and then, the sample No. 3-No. By evaluating 40 characteristics, appropriate values of a to e, x, and y are specified.

=== About the composition of the A site ===
<Ratio of Li>
As shown in Table 1, no. 3-No. The sample of 8 differs in the ratio of Li in the A site. As shown in Table 2, No. 4-No. Sample 7 had better properties than the reference sample. The ratio c of Li at this time is 0.050 ≦ c ≦ 0.057. From the composition of 2, it can be said that 0.040 ≦ c ≦ 0.057 is an appropriate value of Li at the A site.

<Ratio of K>
No. 9-No. The 13 samples differ in the proportion of K at the A site. And No. 10-No. The 12 samples had better characteristics than the reference sample, and the K ratio c at this time was 0.40 ≦ a ≦ 0.52. That is, it can be said that this numerical range is an appropriate value of K at the A site.

<Ratio of Na>
Similar to Li and K above, No. 14-No. The proper value of Na at the A site is obtained from the characteristics of 19 samples. No. 15-No. The 18 samples had better properties than the reference sample, and the Na ratio c at this time was 0.46 ≦ b ≦ 0.54. That is, it can be said that this numerical range is an appropriate value of Na at the A site. In addition, No. In 15-17, both Qm and εr were 1000 or more, and the value of Kp was also excellent. No. 16 and No. In 17, Kp exceeded 30.

=== About the composition of the B site ===
No. 3-No. No. 19 was a piezoelectric material having a different composition at the A site. Next, for the A site, no. 3-No. No. 19 having the most excellent characteristics. Samples having the same composition as that of the sample No. 17 and the composition of the B site being changed are No. 20-30.

<Ta ratio>
No. 20 to 23 are samples in which the ratio of Ta at the B site was changed as shown in Table 1. That is, it is a sample in which the ratio of Nb and Ta is changed while the ratio of Sb is fixed. Note that the ratio of Sb is set to e = 0.04 which is the same as that of the reference sample. And No. The samples 21 and 22 were superior in characteristics to the reference sample, and the Ta ratio d at this time was 0.10 ≦ d ≦ 0.20. That is, it can be said that this numerical range is an appropriate value of Ta at the B site.

<Percentage of Sb>
No. 24 to 30 are samples in which the ratio of Sb at the B site was changed as shown in Table 1. About the ratio of Ta, it is set to e = 0.10 same as a reference | standard sample. And No. The samples of 25 to 29 were superior in characteristics to the reference sample, and the ratio e of Sb at this time was 0.005 ≦ e ≦ 0.04. That is, it can be said that this numerical range is an appropriate value of Sb at the B site.

=== About the addition amount of BaTiO ₃ and CuO ===
No. 1-No. Of the 40 samples, no. 1-No. No. 30 had the same addition amount of BaTiO ₃ and CuO as the reference sample (x = 3, Y = 2). In contrast, no. In 31 to 40, thereby changing the amount of BaTiO ₃ and CuO.

<Amount of BaTiO ₃ added>
As shown in Table 1, no. Nos. 31 to 35 show the composition of the A site and the B site and the added amount of CuO. 1-No. No. 30 with the most excellent characteristics. 17 (No. 21, 29), and the amount of addition of BaTiO ₃ was changed. As shown in Table 2, No. Samples 32 to 34 were superior in characteristics to the reference sample. At this time, the addition amount x of BaTiO ₃ was 3.0 ≦ x ≦ 7.0. That is, it can be said that this numerical range is an appropriate addition amount of BaTiO ₃ .

<Addition amount of CuO>
On the other hand, samples with different amounts of CuO added were No. 36-40. The No. 36 to 40, the composition of the A site and the B site and the addition amount of BaTiO ₃ were No. Same as 17 samples. As shown in Table 2, No. Samples 37 to 39 were superior in characteristics to the reference sample. At this time, the addition amount y of CuO was 2.0 ≦ y ≦ 4.0. That is, this numerical range is an appropriate addition amount of CuO.

=== About the optimal composition of the A site ===
From the above, it is a condition that the piezoelectric material according to the embodiment of the present invention includes the following items (1) to (4) as requirements.

(1) A piezoelectric material represented by the general formula (K _a Na _b Li _c ) (Nb Bd _e Ta _d Sb _e ) O ₃ + xmol% BaTiO ₃ + ymol% CuO.
(2) B = 1.1.
(3) a + b ≧ 0.96.
(4) 0.40 ≦ a ≦ 0.52, 0.46 ≦ b ≦ 0.54, 0.040 ≦ c ≦ 0.057, 0.10 ≦ d ≦ 0.20, 0.005 ≦ e ≦ 0 0.04, 3.0 ≦ x ≦ 7.0, 2.0 ≦ y ≦ 4.0.

  Here, when the results shown in Table 2 are reexamined, It can be seen that the characteristics of the samples 6, 10, 15 to 17 are extremely excellent. Both Qm and εr are 900 or more, and Kp is as high as about 30 to 35%. Further, when the characteristics of the samples with the numbers before and after these samples are seen, for example, No. 10 to 12 are constant as long as the ratio of Na in the A site is a + b ≧ 0.96, and the ratio of K is changed. And No. In the samples 10 to 12, there is a tendency that the characteristics of Qm and εr are traded off depending on the ratio of K. Specifically, the larger the K ratio, the better the εr characteristic and the lower the Qm characteristic. About Kp, it is improving, so that the ratio of K is large.

  On the other hand, No. changing the ratio of Na in the A site. Among samples 15 to 18, No. In 15-17, all the characteristics of Kp, Qm, and εr are improved. In particular, no. 16 and 17, Qm was 1000 or more.

  Therefore, no. In No. 16 sample, the ratio of K was slightly increased, and the composition of the A site was set to a = b = 0.50 and c = 0.056. Forty-one samples were manufactured and properties were measured.

In Table 3 and Table 4, No. The composition and piezoelectric properties of 41 samples were shown.

  No. of the composition shown in Table 3. 41, as shown in Table 4, Kp was 35 or more, and Qm and εr were 1000 or more.

=== About the firing conditions ===
The present inventor previously discovered that even a piezoelectric material having the same composition is superior in characteristics when fired in an oxygen atmosphere than when fired in the air. A patent application was filed (Japanese Patent Application No. 2011-256486). Therefore, the piezoelectric material according to the example of the present invention was examined as to whether or not the characteristics were improved by firing in an oxygen atmosphere. In this examination, No. having a different composition of the A site. 11, 17, and 41 were extracted as comparison targets, and a piezoelectric material having the same composition as the extracted sample was baked in an oxygen atmosphere, and the characteristics of the piezoelectric material were measured.

Table 5 shows the composition of the sample to be compared.

Table 6 shows the comparison results of the piezoelectric characteristics depending on the firing conditions.

  In Table 6, the sample with “B” after the sample number is a piezoelectric material fired in an oxygen atmosphere, and all the characteristics of Kp, Qm, and εr for all the piezoelectric materials to be compared. Improved. From the above results, the piezoelectric material specified by the above (1) to (4) is not limited to the composition of the sample to be compared, and further enhancement of characteristics can be expected by firing in an oxygen atmosphere. .

  The present invention can be used for devices and elements using piezoelectricity such as a piezoelectric buzzer and an ultrasonic motor.

DESCRIPTION OF SYMBOLS 1 Piezoelectric element, 2 disc-shaped piezoelectric material, 3 silver electrode, s1 raw material mixing | blending process, s2 temporary baking process, s6 baking process

Claims (3)

A piezoelectric material represented by _a general formula (K _a Na _b Li _c ) (Nb Bd _e Ta _d Sb _e ) O ₃ + xmol% BaTiO ₃ + ymol% CuO,
B = 1.1, a + b ≧ 0.96,
0.4 ≦ a ≦ 0.52, 0.46 ≦ b ≦ 0.54, 0.040 ≦ c ≦ 0.057, 0.1 ≦ d ≦ 0.2, 0.005 ≦ e ≦ 0.04, 3 ≦ x <7, 2 ≦ y ≦ 4,
A piezoelectric material characterized by that.   2. The piezoelectric material according to claim 1, wherein the electromechanical coupling coefficient Kp, the relative dielectric constant εr, and the mechanical quality factor Qm are Kp ≧ 30%, εr ≧ 900, and Qm ≧ 900, respectively. A method of manufacturing the piezoelectric material according to claim 1 or 2,
A mixing step of mixing a raw material of a compound to be the piezoelectric material and a solvent;
A pre-baking step of baking the mixture of the compound and the solvent at a predetermined temperature lower than a sintering temperature;
A molding step of molding a mixture obtained by adding a binder to the mixture after the preliminary firing step into a predetermined shape;
A firing step of sintering the molded product obtained in the molding step in an oxygen atmosphere;
A method for producing a piezoelectric material, comprising:

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