Potassium sodium niobate-based lead-free piezoelectric transparent ceramic and preparation method thereof

Abstract

The present invention discloses a sodium potassium niobate-based lead-free piezoelectric transparent ceramic and a preparation method thereof. The general chemical composition formula of the ceramic is: (K 0.5 Na 0.5 ) 0.98 Eu 0.02 NbO3: x Yb, where x is the molar fraction of component Yb, and 0.01 ≤ x ≤ 0.02. The embodiment of the present invention provides a sodium potassium niobate-based lead-free piezoelectric transparent ceramic. The transparent ceramic has good light transmittance, luminescence performance, electrical properties, and photochromic ability. This novel ceramic with both luminescence and electrical properties has a very wide range of applications.

Description

Technical Field

[0001] The invention relates to the field of functional ceramics, and in particular to a potassium sodium niobate-based lead-free piezoelectric transparent ceramic and a preparation method thereof. Background Art

[0002] Rare earth ion doped luminescent materials have broad application prospects in the fields of lasers, volumetric three-dimensional displays, phosphors and oriented films due to their excellent luminescent properties. In recent years, rare earth doped photochromic materials have attracted people's attention. Photochromic materials have great application potential in information storage, optical anti-counterfeiting and other aspects. To achieve high luminous efficiency, one possible path is to prepare transparent ceramics; to make rare earth doped luminescent materials have certain electrical properties, one possible path is to dope ferroelectric materials as a matrix. Therefore, rare earth doped transparent ferroelectric ceramics have become a hot research topic.

[0003] Photochromic materials are mainly divided into two categories: organic photochromic materials and inorganic photochromic materials. Among them, inorganic photochromic materials have become a hot topic of research due to their excellent cycle performance and high photochromic sensitivity. After the inorganic matrix is ​​doped with rare earth ions, on the one hand, the rare earth ions can be used as the luminescence center of the matrix to realize photoluminescence, and on the other hand, the luminescence intensity of the rare earth ions can be reversibly modulated in the photochromic reaction. In this process, the inorganic photochromic material will not produce irreversible changes, and information can be written and erased cyclically.

[0004] At present, the only transparent ferroelectric ceramics with certain applications are lead zirconate titanate-doped lithium-based ceramics. As we all know, lead is a toxic element, and lead zirconate titanate-based ceramics have a high lead content, which is easy to cause the volatilization of lead during production, use and waste treatment, which is a huge threat to the ecological environment and human health. Therefore, many countries and regions have issued some laws or directives to restrict the use of harmful elements such as lead in electronic devices.

[0005] Especially in recent years, with the gradual improvement of people's environmental awareness and from the perspective of building sustainable development, it is urgent to develop high-performance lead-free ceramics that can replace lead-based transparent ceramics. Among the many lead-free piezoelectric systems, potassium sodium niobate-based ceramics have received widespread attention due to their excellent performance. Some researchers have found that potassium sodium niobate-based piezoelectric ceramics not only have excellent electrical properties, but also have good luminescence properties and transparency when doped with specific elements. Therefore, the research on the optoelectronic properties of potassium sodium niobate-based ceramics has attracted many researchers to participate.

[0006] However, it is difficult to balance the luminescence, transparency, and piezoelectric properties of potassium sodium niobate-based ceramics. Therefore, how to retain certain piezoelectric properties while achieving good transparency and luminescence performance is a problem that researchers urgently need to solve. When irradiating ceramics, how to obtain ceramics that can achieve fast response photochromism so that optical information can be quickly written and erased is also one of the current focuses of research on potassium sodium niobate-based optoelectronic ceramics. Summary of the invention

[0007] The purpose of the present invention is to provide a potassium sodium niobate-based ceramic that can take into account transparency, luminescence performance, and piezoelectric performance, has the characteristics of fast response photochromism, the luminescence attenuation after photochromism is large enough, and the photochromic cycle performance is good. Information can be repeatedly written and erased to ensure that the ceramic can be used in optical information storage, optical anti-counterfeiting and other fields.

[0008] In order to achieve the above object, a technical solution adopted by the present invention is:

[0009] A lead-free piezoelectric transparent ceramic based on potassium sodium niobate, the general chemical composition formula is:

[0010] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 NbO3: x Yb, where x is the molar fraction of the component Yb, 0.01 ≤ x ≤ 0.02.

[0011] Preferably, x Are 0.01, 0.015, and 0.02.

[0012] Preferably, the potassium sodium niobate-based lead-free piezoelectric transparent ceramic has the following characteristics:

[0013] (1) Piezoelectric constant of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic d 33 20~30 pC / N;

[0014] (2) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has a light transmittance of 20% to 40% at 1000 nm;

[0015] (3) The strongest excitation light wavelength of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic is 465-466 nm;

[0016] (4) The luminescence lifetime of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic at 610 nm under 465 nm light excitation is 833-878 μs;

[0017] (5) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic changes color fully within 10 seconds under 407 nm violet light irradiation;

[0018] (6) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has a down-conversion luminescence attenuation of 65% to 75%, and an up-conversion luminescence attenuation of 50% to 70%.

[0019] The second technical solution adopted by the present invention is:

[0020] A method for preparing potassium sodium niobate-based lead-free piezoelectric transparent ceramics, comprising:

[0021] The raw material components are weighed according to the general chemical composition formula, and the potassium sodium niobate-based lead-free piezoelectric transparent ceramic is prepared by a solid phase sintering method.

[0022] Preferably, the solid phase sintering method includes pre-sintering and sintering, and the sintering is divided into the following heating stages:

[0023] The sintering temperature was increased to 800 °C at a heating rate of 5 °C / min; then increased to 1125 °C at a heating rate of 1 °C / min and kept at this temperature for 3 h, and then increased to 1155 °C at a heating rate of 1 °C / min and kept at this temperature for 3 h; then decreased to 1000 °C at a cooling rate of 1 °C / min and ended the program by cooling to room temperature to complete the sintering.

[0024] Preferably, the solid phase sintering method specifically comprises the following steps:

[0025] ball-milling the raw material components to obtain a wet powder slurry;

[0026] Drying and pre-calcining the wet powder slurry to obtain a powder;

[0027] The powder is ball-milled for a second time and dried to obtain dry powder;

[0028] Adding a binder to the dry powder, grinding, drying, sieving, and then pressing to form an embryo;

[0029] The embryo body is debinded, sintered, silver treated, and polarized to obtain the potassium sodium niobate-based lead-free piezoelectric transparent ceramic.

[0030] Preferably, the pre-calcination is performed at 850° C. for 6 hours.

[0031] Preferably, the specific method of adding a binder to the dry powder, grinding, drying, sieving and then pressing to form is:

[0032] Add a binder to the dry powder, grind it uniformly to form flocculent particles, continue to add a binder after drying, grind to obtain flocculent particles, dry and sieve to obtain fine powder, and press the fine powder into an embryo.

[0033] Preferably, the debinding is performed by debinding the embryo at 850° C. for 2 h and then cooling the embryo to room temperature.

[0034] Preferably, the process parameters of the silver treatment are: heating to 600°C and keeping the temperature for 10 min;

[0035] The process parameters of the polarization treatment are: the polarization electric field is 30 ~ 50 kV / cm, and the polarization time is 10 min.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention achieves good red light emission and optical transparency by doping with the rare earth element Eu, and achieves up-conversion luminescence by doping with the rare earth element Yb. The potassium sodium niobate-based lead-free piezoelectric transparent ceramic provided by the present invention has high transparency, a transmittance of up to 40% at 1000 nm, and an ultra-sensitive transition phenomenon at 465 nm. The irradiation results show that the ceramic has the characteristics of fast response photochromism, and can fully change color after 10 seconds of ultraviolet light irradiation. The luminescence attenuation after color change is up to more than 70%, and the photochromic cycle performance is good, and information can be repeatedly written and erased, making it valuable for practical applications.

[0038] The method for preparing the potassium sodium niobate-based lead-free piezoelectric transparent ceramic provided in the embodiment of the present invention can be prepared using industrial raw materials, and the preparation process is simple and stable, and equipment can be used to achieve mass production, which is convenient for industrial production. The present invention provides a lead-free, environmentally friendly piezoelectric ceramic that will not cause harm to the human body and the ecological environment during the production process, and is more in line with environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Graphs showing the light transmittance of potassium sodium niobate-based lead-free piezoelectric transparent ceramics prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0040] Figure 2 1 is a scanning electron microscope image of the potassium sodium niobate-based lead-free piezoelectric transparent ceramics prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0041] Figure 3 The quasi-static state of the lead-free piezoelectric transparent ceramics based on potassium sodium niobate prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention is d 33 picture;

[0042] Figure 4 The diagrams are up-conversion luminescence and down-conversion luminescence of the potassium sodium niobate-based lead-free piezoelectric transparent ceramics prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0043] Figure 5 It is a photochromic image of potassium sodium niobate-based lead-free piezoelectric transparent ceramics prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0044] Figure 6 It is a graph showing the variation of the luminescence intensity of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic obtained in Example 3 of the present invention with the pump light power and a luminescence mechanism graph drawn based on the graph. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It is worth noting that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0046] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0047] The first embodiment of the present invention provides a lead-free piezoelectric transparent ceramic based on potassium sodium niobate, and the chemical composition formula of the transparent ceramic is:

[0048] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 NbO3: x Yb, where x is the molar fraction of the component Yb, 0.01≤ x ≤ 0.02.

[0049] It should be noted that the potassium sodium niobate-based lead-free piezoelectric transparent ceramic provided in the embodiment of the present invention is a lead-free piezoelectric transparent ceramic based on K 0.5 Na 0.5 On the basis of NbO3 ceramic matrix, doping components Yb2O3 and Eu2O3 realize the transparency and luminescence of ceramics. Among them, doping of Eu element A improves the transparency of ceramics, and Eu as the luminescence center of ceramics realizes luminescence; doping of Yb element B realizes up-conversion luminescence. Doping of Yb element reduces transparency, but improves luminescence intensity and photochromic luminescence modulation ratio, and at the same time causes certain changes in the crystal symmetry of ceramics, which is specifically manifested in spectral line shift and energy level splitting.

[0050] In the actual preparation process, in order to ensure the stability of production, K2CO3 is used as the K source, Na2CO3 is used as the Na source, and Nb2O5 is used as the Nb source.

[0051] It is worth mentioning that in the potassium sodium niobate-based lead-free piezoelectric transparent ceramic provided in the above embodiment, except for the content of the component Yb in the chemical composition formula of the ceramic material, the content ratios of other elements are fixed. 0.5 Na 0.5 ) 0.98 Eu 0.02 NbO3: x In the "Yb" component, the atomic ratio of K element, Na element, Nb element, Eu element and O element is 0.49: 0.49: 1: 0.02: 3.

[0052] In some preferred embodiments of the present invention, x The general formulas of potassium sodium niobate-based lead-free piezoelectric transparent ceramics are:

[0053] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 Yb 0.01 O3;

[0054] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 Yb 0.015 O3;

[0055] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 Yb 0.02 O3.

[0056] After testing, the transmittance of this potassium sodium niobate-based lead-free piezoelectric transparent ceramic at 1000 nm was 20%~40%, and the photochromic luminescence attenuation was 50%~75%.

[0057] It should be noted that it is difficult to take into account the transparency, luminescence, fast response photochromic and piezoelectric properties of potassium sodium niobate-based ceramics, and it is especially difficult to obtain piezoelectric transparent ceramics with all the characteristics. The ceramics provided by the present invention have gradient transparency, luminescence and piezoelectric properties, and all have the characteristics of fast response photochromic properties, and have excellent performance.

[0058] Specifically, the potassium sodium niobate-based lead-free piezoelectric transparent ceramic has the following characteristics:

[0059] (1) Piezoelectric constant of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic d 33 20~30 pC / N;

[0060] (2) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has a light transmittance of 20% to 40% at 1000 nm;

[0061] (3) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has an ultra-sensitive transition phenomenon, and the strongest excitation light wavelength is 465-466 nm;

[0062] (4) The luminescence lifetime of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic at 610 nm under 465 nm light excitation is 833-878 μs;

[0063] (5) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has a fast-response photochromic phenomenon, and under 407 nm violet light irradiation, the color changes completely within 10 seconds;

[0064] (6) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has a high photochromic luminescence attenuation, with a down-conversion luminescence attenuation of 65% to 75% and an up-conversion luminescence attenuation of 50% to 70%.

[0065] The potassium sodium niobate-based lead-free piezoelectric transparent ceramic provided by the embodiment of the present invention has high luminous intensity, good transparency, good piezoelectric performance, and large luminous attenuation after photochromism. In addition, since the piezoelectric ceramic material provided by the embodiment of the present invention is an environmentally friendly material that does not contain lead, it is more in line with environmental protection requirements and is expected to be widely used.

[0066] The second embodiment of the present invention provides a method for preparing potassium sodium niobate-based lead-free piezoelectric transparent ceramics.

[0067] The preparation method adopted by the present invention is a commonly used solid phase sintering method to prepare the potassium sodium niobate-based lead-free piezoelectric transparent ceramic.

[0068] The solid phase sintering method includes the steps of pre-sintering and sintering. The sintering procedure has a great influence on transparent ceramics. High-quality transparent ceramics require precise control of the sintering temperature. The sintering is divided into the following heating stages: the sintering temperature is increased to 800 °C at a heating rate of 5 °C / min; then the temperature is increased to 1125 °C at a heating rate of 1 °C / min and kept at this temperature for 3 h, and then the temperature is increased to 1155 °C at a heating rate of 1 °C / min and kept at this temperature for 3 h; the temperature is reduced to 1000 °C at a cooling rate of 1 °C / min, and then the procedure is ended and cooled to room temperature to complete the sintering.

[0069] It should be noted that in this embodiment, the temperature is first quickly raised to 800°C, which can save time on the one hand, and on the other hand, the temperature control at this stage does not need to be very precise. When the temperature rises to above 800°C, the heating rate needs to be reduced. On the one hand, if the heating rate is too fast, it is easy to cause the temperature to exceed the required 1125°C, and the heating rate is too fast, which will cause the grains to grow too fast, which is not conducive to the removal of pores, making the pores unevenly distributed, affecting the density of the material, and causing problems with the product. On the other hand, it can increase the life of the sintering furnace.

[0070] In some specific embodiments, the solid phase sintering method specifically comprises the following steps:

[0071] ball-milling the raw material components to obtain a wet powder slurry;

[0072] Drying and pre-calcining the wet powder slurry to obtain a powder;

[0073] The powder is ball-milled for a second time and dried to obtain dry powder;

[0074] Adding a binder to the dry powder, grinding, drying, sieving, and then pressing to form an embryo;

[0075] The embryo body is debinded, sintered, silver treated, and polarized to obtain the potassium sodium niobate-based lead-free piezoelectric transparent ceramic.

[0076] For the specific process parameters of other steps besides solid-phase sintering, such as ball milling, drying, pre-firing, debinding, pressing, silver treatment, polarization treatment, etc., in actual production, those skilled in the art can make adaptive adjustments based on the solid-phase sintering method commonly used for piezoelectric ceramics and actual conditions without special limitations.

[0077] For example, the raw material components are ball-milled to obtain a wet powder slurry, which can be as follows: the raw material components are proportioned according to the general chemical composition formula, anhydrous ethanol is used as a medium, and after planetary ball milling in a ball mill for 12 hours, a uniformly mixed wet powder is obtained; wherein the ball mill is a nylon mill, and the grinding balls in the ball mill are ZrO2 balls.

[0078] The drying and pre-calcining of the wet powder slurry to obtain the powder may be: drying the wet powder and then pre-calcining it, the pre-calcining temperature is increased to 850° C. at a heating rate of 3° C. / min and kept at that temperature for 6 h, and then cooled to room temperature to obtain the powder.

[0079] The second ball milling and drying of the powder to obtain dry powder can be as follows: the powder is poured into a ball mill, anhydrous ethanol is added, and after 12 hours of planetary ball milling, a uniform wet powder is obtained, and the wet powder is dried to obtain dry powder; wherein the ball mill is a nylon mill, and the grinding balls in the ball mill are ZrO2 balls.

[0080] The step of adding a binder to the dry powder, grinding, drying, sieving, and then pressing to form an embryo can be as follows: adding 8% PVA to the dry powder, grinding evenly to form flocculent particles, drying, and then continuing to add 8% PVA to form flocculent particles, drying, and then passing through a 100-mesh sieve to obtain coarse powder and fine powder; then pressing the fine powder into an embryo with a diameter of 10 mm and a thickness of 1 mm under a pressure of 400 MPa; wherein the 8% PVA is a mixed solution of polyvinyl alcohol and deionized water, and the mass proportion of polyvinyl alcohol is 8%.

[0081] The debinding is to debind the embryo body at 850° C. for 2 h and then cool it to room temperature to obtain a debinded embryo body.

[0082] The silver treatment and polarization treatment can be: silver electrodes are placed on the two surfaces of the sintered ceramic material, the temperature is raised to 600°C and kept warm for 10 minutes; a withstand voltage tester is used to polarize the ceramic material with the silver electrodes burned in silicone oil at room temperature, the polarization electric field is 30 to 50 kV / cm, and the polarization time is 10 minutes.

[0083] The method for preparing the potassium sodium niobate-based lead-free piezoelectric transparent ceramic provided in the embodiment of the present invention can be prepared using industrial raw materials, and the preparation process is stable, and equipment can be used to achieve mass production, which is convenient for industrial production.

[0084] The potassium sodium niobate-based lead-free piezoelectric transparent ceramics and their properties provided by the above-mentioned embodiments of the present invention will be described in detail below with reference to specific examples.

[0085] Example 1

[0086] The chemical composition of potassium sodium niobate-based lead-free piezoelectric transparent ceramics is:

[0087] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 Yb 0.01 O3, that is x is 0.01.

[0088] The preparation method of the transparent ceramic is as follows:

[0089] (1) Weigh 3.4203 g K2CO3, 2.6020 g Na2CO3, 13.2971 g Nb2O5, 0.3520 g Eu2O3, and 0.1971 g Yb2O3 of analytically pure material as raw materials and prepare the ingredients.

[0090] (2) The weighed raw materials were milled with anhydrous ethanol as the medium by planetary ball milling for 12 h and then dried to obtain a uniformly mixed dry powder. The obtained dry powder was then pre-calcined at 850 °C for 6 h.

[0091] (3) The pre-calcined powder is milled with anhydrous ethanol as the medium, and then dried to obtain a uniformly mixed dry powder.

[0092] (4) Add 8% PVA to the powder after the second ball milling, and evenly grind to form flocculent particles. After drying, continue to add 8% PVA, grind to obtain flocculent particles, and dry and pass through a 100-mesh sieve to obtain fine powder. The powder that is not sieved is coarse powder.

[0093] (5) The fine powder is pressed into a body with a diameter of 10 mm and a thickness of 1 mm at a pressure of 400 MPa.

[0094] (6) Debinding the embryo at 850°C.

[0095] (7) Sintering the debinded green body at 1155°C.

[0096] (8) Silver electrodes were applied on both surfaces of the sintered ceramic sample and the silver was sintered at 600 °C for 10 min for later use.

[0097] (9) The ceramic sample with silver electrodes was placed in silicone oil at room temperature for polarization with an electric field of 30-50 kV / cm and a polarization time of 10 min.

[0098] Example 2

[0099] The chemical composition of potassium sodium niobate-based lead-free piezoelectric transparent ceramics is:

[0100] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 Yb 0.015 O3, that is x is 0.015.

[0101] The preparation method of the transparent ceramic is the same as that of Example 1, and the similarities are not repeated here. The difference is that the mass of the raw materials is weighed and prepared according to the chemical formula in Example 2 to obtain a dry sheet.

[0102] Example 3

[0103] The chemical composition of potassium sodium niobate-based lead-free piezoelectric transparent ceramics is:

[0104] (K 0.5 Na 0.5 ) 0.98 Eu0.02 Yb 0.02 O3, that is x is 0.02.

[0105] The preparation method of the transparent ceramic is the same as that of Example 1, and the similarities are not repeated here. The difference is that the mass of the raw materials is weighed and prepared according to the chemical formula in Example 3 to obtain a dry sheet.

[0106] Comparative Example 1

[0107] The chemical composition of potassium sodium niobate-based lead-free piezoelectric transparent ceramics is:

[0108] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 NbO3, namely x is 0.

[0109] The preparation method of the transparent ceramic is the same as that of Example 1, and the similarities are not repeated here. The difference is that the mass of the raw materials is weighed and prepared according to the chemical formula in Comparative Example 1 to obtain a dry sheet.

[0110] Comparative Example 2

[0111] The chemical composition of potassium sodium niobate-based lead-free piezoelectric transparent ceramics is:

[0112] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 Yb 0.005 O3, that is x is 0.005.

[0113] The preparation method of the transparent ceramic is the same as that of Example 1, and the similarities are not repeated here. The difference is that the mass of the raw materials is weighed and prepared according to the chemical formula in Comparative Example 2 to obtain a dry sheet.

[0114] Comparative Example 3

[0115] The chemical composition of potassium sodium niobate-based lead-free piezoelectric transparent ceramics is:

[0116] (K 0.5 Na 0.5 ) 0.98 Eu 0.02 Yb 0.025 O3, that is x is 0.025.

[0117] The preparation method of the transparent ceramic is the same as that of Example 1, and the similarities are not repeated here. The difference is that the mass of the raw materials is weighed and prepared according to the chemical formula in Comparative Example 3 to obtain a dry sheet.

[0118] Figure 1 It is a transparency diagram of the potassium sodium niobate-based lead-free piezoelectric transparent ceramics prepared in Examples 1-3 of the present invention and Comparative Examples 1-3.

[0119] like Figure 1 As shown, it can be seen that with the increase of Yb doping amount, the transmittance of the ceramic piece gradually decreases, which is basically consistent with the transparency of the actual ceramic sample in the illustration; the transparency of the shaded part in the figure at 920 nm, 950 nm, and 980 nm decreases because of the absorption of light by Yb ions. It is generally believed that the absorption peak of Yb ions is 980 nm, but in low-symmetry cubic crystals, the energy levels of Yb ions will split, resulting in multiple absorption peaks. The greater the Yb ion doping amount, the more obvious the decrease in transparency; the transmittance of the ceramic piece below 400nm is close to 0, which is due to the interband transition of the ceramic piece. When x =0.025, the light transmittance of the ceramic has dropped below 20%, the ceramic color is darker and the performance is poor.

[0120] Figure 2 It is a scanning electron microscope image of the potassium sodium niobate-based lead-free piezoelectric transparent ceramics prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0121] like Figure 2 As shown, when x =0, 0.005, 0.01, 0.015, 0.02, 0.025, the corresponding geometric mean grain sizes are 0.2510 μm, 0.2450 μm, 0.2063 μm, 0.2017 μm, 0.1946 μm, 0.1708 μm, respectively. It can be seen that with the increase of Yb 3+ With the increase of content, the grain size of ceramics gradually decreases.

[0122] Figure 3 The quasi-static state of the lead-free piezoelectric transparent ceramics based on potassium sodium niobate prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention is d 33 picture.

[0123] like Figure 3 As shown in Figure 2, it can be seen that with the increase of Yb content, the quasi-static d 33 The decrease in piezoelectric performance can be explained by the local distortion of the crystal, which produces polar nanoregions (PNRs). + and Na+ By Eu 3+ After substitution, since the ionic radius and valence state of the two are different, the mismatch of ionic radius forms a local elastic field, and the mismatch of valence state forms a local electric field. The interaction between the two will produce a large number of PNRs, which explains why the piezoelectric performance of the prepared ceramics is biased; Nb at the B site 5+ By Yb 3+ After substitution, both have the same problem of mismatch between ionic radius and valence state. This can also explain why Yb 3+ The greater the doping amount, the worse the piezoelectric performance. The presence of a large number of PNRs will lead to the formation of a pseudocubic phase, which can reduce light scattering and improve transparency on the one hand, but on the other hand will reduce the piezoelectric performance of the ceramic. x =0.025, ceramic d 33 It drops to 15 pC / N, which is poor performance.

[0124] Figure 4 The diagrams are up-conversion luminescence and down-conversion luminescence of the potassium sodium niobate-based lead-free piezoelectric transparent ceramics prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention, wherein: (a) is down-conversion luminescence; (b) is up-conversion luminescence.

[0125] like Figure 4 As shown, Figure 5 (a) is the emission spectrum of the ceramic sample under 465 nm light excitation. x = 0, the sample 5 D0→ 7 The F1 emission peak is still a single peak, but with the Yb 3+ As the doping amount increases, the single peak splits into two peaks, which may be due to the fact that Yb 3+ Doping substitution Nb 5+ After the position is changed, the crystal field is distorted and the symmetry of the crystal is reduced, resulting in the occurrence of energy level splitting. From the figure, we can also observe the occurrence of spectral line shift. x =0.01, 5 D0→ 7 The peak of the F1 transition shifts from 593 nm to 594 nm, and signs of energy level splitting can be observed. 5 D0→ 7 The peak of F2 transition shifted from 614 nm to 612 nm. The reason for the line shift may be the addition of Yb 3+ Replace Nb 5+ This causes the electronegativity of the next-nearest neighboring atoms of the luminescent center to change. 5 D0→ 7 The F2 transition luminescence intensity increases with the Yb 3+The increase in doping amount first increases and then decreases. The reason for the increase in luminescence intensity is that the 465 nm light converts Eu 3+ Inspired 5 D2 level, then Eu 3+ Radiation-free transition to 5 D1 energy level, which will 7 F6 energy level transitions and transfers energy to Yb 3+ , so that it 2 F 7 / 2 Jump to 2 F 5 / 2 , while releasing phonons of a certain energy, and then Eu can be converted into 3+ Excitation to a higher energy level induces Eu 3 + The possible reason for the decrease in luminescence intensity is the concentration quenching effect, that is, Yb 3+ Excessive concentration leads to a large number of non-radiative transitions and energy transfer. Figure 5 (b) is the upconversion luminescence spectrum of the ceramic sample obtained under 980 nm laser excitation. x = 0, the ceramic does not emit light. 3+ When the doping amount is small, the luminescence is also weak, indicating that the upconversion luminescence is completely generated by Yb 3+ Dominant. When up-conversion luminescence occurs, the ceramic 5 D0→ 7 The F2 transition luminescence intensity increases with the Yb 3+ The increase in doping amount is due to the fact that Yb 3+ As the only component in the ceramic that can absorb 980 nm light and transition to a high energy level, its concentration increase can promote more Yb 3+ Reaching a high energy level, thereby making more Eu 3+ Transition to a high energy level, enhancing the upconversion luminescence of the ceramic. In order to achieve strong upconversion luminescence, it is necessary to ensure that the doping amount of Yb is large enough. In this experiment, it was found that x ≥0.01 can effectively promote upconversion luminescence.

[0126] Figure 5 The graphs of up-conversion luminescence and down-conversion luminescence of potassium sodium niobate-based lead-free piezoelectric transparent ceramics prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention are shown. Among them: (a) is the comparison of luminescence intensity before and after down-conversion luminescence photochromism; (b) is the cycle life of down-conversion luminescence photochromism; (c) is the comparison of luminescence intensity before and after up-conversion luminescence photochromism; (d) is the summary of photochromic luminescence attenuation value.

[0127] like Figure 5 As shown, Figure 5(a) is the luminescence spectrum of the ceramic sample before and after irradiation. The dark curve is the luminescence spectrum before irradiation, and the light curve is the luminescence spectrum after irradiation. It can be seen from the figure that the luminescence intensity of the ceramic generally weakens after irradiation. Here, we define a parameter ΔR I Characterize the degree of change in luminous intensity before and after irradiation ,in R 0 is the luminous intensity before irradiation, R 1 is the luminous intensity after irradiation. In order to characterize the cycle performance of the ceramic sheet, we also conducted cycle tests, such as Figure 5 (b) is shown. Figure 5 (b) The change in luminous intensity before irradiation and after irradiation heating and recovery ,in R 0 is the luminous intensity before irradiation, R 2 It is the luminous intensity after irradiation and reheating. From the figure, it can be seen that the ceramic sheet has good cycle performance. After irradiation, it can be restored to its original state by heating, and its luminous performance does not change much. Figure 5 (c) is the spectrum of upconversion luminescence before and after irradiation, the ceramic sample x =0, 0.005, 0.01 have lower luminous intensity, and their enlarged images have also been marked. Figure 5 (d) is the calculated ΔR I From the summary, we can see that the down-conversion luminescence ΔR I are relatively large, showing a greater modulation effect, while the modulation effect is not obvious when the upconversion luminescence is weak, but when the doping amount x ≥0.01, it also begins to show a greater modulation effect. Regardless of up-conversion luminescence or down-conversion luminescence, when x =0.02, the maximum luminescence modulation effect is shown. This is the result of two reasons. On the one hand, the ceramic component is most likely to produce more defects. After irradiation, a large number of color centers are formed, which leads to a large amount of non-radiative resonant energy transfer, thereby inhibiting the Eu 3+ The radiation transition of x =0.02 The up-conversion luminescence and down-conversion luminescence of the ceramic with this component are both relatively large, so the luminescence intensity changes significantly, showing a relatively large modulation effect. The relatively large modulation effect provides the possibility for the ceramic to be used in optical information storage, optical anti-counterfeiting or optoelectronic multifunctional devices.

[0128] Figure 6 The graph of the luminescence intensity of the lead-free piezoelectric transparent ceramic based on potassium sodium niobate obtained in Example 3 of the present invention as a function of the pump light power and the luminescence mechanism diagram drawn based on the graph. Among them: (a) is the spectrum obtained by changing the pump light power; (b) is the record5 D0→ 7 (c) is the fitting diagram obtained by processing the F2 transition luminescence intensity data; (c) is the up-down conversion luminescence mechanism diagram of the ceramic.

[0129] like Figure 6 As shown, Figure 6 (a) is to take x =0.02 ceramic, change the laser power to measure the luminous intensity, the luminous intensity and laser power have a relationship I∝W n , where I is the luminous intensity, W is the laser power, and n is the number of photons absorbed by the luminescent ion from the ground state to the excited state. 5 D0→ 7 The F2 transition luminescence intensity was recorded and processed together with the laser power to obtain Figure 6 (b), which means that the number of photons absorbed by the luminescent ion from the ground state to the excited state is about 2, and the upconversion luminescence is a two-photon process. Based on this, we draw the energy level transition mechanism diagram of up-conversion luminescence, as shown in Figure 6 (c) As shown in this figure, we can explain the luminescence peak of the ceramic in detail and understand the energy level transition mode of the system.

[0130] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A potassium sodium niobate-based lead-free piezoelectric transparent ceramic, characterized in that: The general chemical formula is: (K 0.5 Na 0.5 ) 0.98 Eu 0.02 NbO3: xYb, wherein x is the molar fraction of the component Yb, 0.01≤ x ≤ 0.02; Yb element is doped in the B position.

2. The potassium sodium niobate-based lead-free piezoelectric transparent ceramic according to claim 1, characterized in that: x is 0.01, 0.015, and 0.

02.

3. The potassium sodium niobate-based lead-free piezoelectric transparent ceramic according to any one of claims 1 to 2, characterized in that: The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has the following characteristics: (1) The piezoelectric constant d of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic 33 20~30 pC / N; (2) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has a light transmittance of 20% to 40% at 1000 nm; (3) The strongest excitation light wavelength of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic is 465-466 nm; (4) The luminescence lifetime of the potassium sodium niobate-based lead-free piezoelectric transparent ceramic at 610 nm under 465 nm light excitation is 833-878 μs; (5) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic changes color fully within 10 seconds under 407 nm violet light irradiation; (6) The potassium sodium niobate-based lead-free piezoelectric transparent ceramic has a down-conversion luminescence attenuation of 65% to 75%, and an up-conversion luminescence attenuation of 50% to 70%.

4. A method for preparing a potassium sodium niobate-based lead-free piezoelectric transparent ceramic according to any one of claims 1 to 3, characterized in that: include: Weighing various raw material components according to the chemical composition formula, and preparing the potassium sodium niobate-based lead-free piezoelectric transparent ceramic by solid phase sintering method; The solid phase sintering method includes pre-sintering and sintering, and the sintering is divided into the following heating stages: The sintering temperature was increased to 800 °C at a heating rate of 5 °C / min; then increased to 1125 °C at a heating rate of 1 °C / min and kept at this temperature for 3 h, and then increased to 1155 °C at a heating rate of 1 °C / min and kept at this temperature for 3 h; then decreased to 1000 °C at a cooling rate of 1 °C / min and ended the program by cooling to room temperature to complete the sintering.

5. The preparation method according to claim 4, characterized in that: The solid phase sintering method specifically comprises the following steps: ball-milling the raw material components to obtain a wet powder slurry; Drying and pre-calcining the wet powder slurry to obtain a powder; The powder is ball-milled for a second time and dried to obtain dry powder; Adding a binder to the dry powder, grinding, drying, sieving, and then pressing to form an embryo; The embryo body is debinded, sintered, silver treated, and polarized to obtain the potassium sodium niobate-based lead-free piezoelectric transparent ceramic.

6. The preparation method according to claim 4 or 5, characterized in that: The pre-sintering is performed at 850° C. for 6 hours.

7. The preparation method according to claim 5, characterized in that: The specific method of adding a binder to the dry powder, grinding, drying, sieving and then pressing to form is: Add a binder to the dry powder, grind it uniformly to form flocculent particles, continue to add a binder after drying, grind to obtain flocculent particles, dry and sieve to obtain fine powder, and press the fine powder into an embryo.

8. The method according to claim 5, characterized in that The debinding is performed by debinding the embryo at 850° C. for 2 h and then cooling the embryo to room temperature.

9. The method according to claim 5, characterized in that The process parameters of the silver treatment are: heating to 600°C and keeping the temperature for 10 min; The process parameters of the polarization treatment are: the polarization electric field is 30 ~ 50 kV / cm, and the polarization time is 10 min.

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