Porous barium titanate single crystal as well as preparation method and application thereof

Abstract

The invention discloses a porous barium titanate single crystal and a preparation method and application thereof, and belongs to the technical field of piezoelectric single crystal materials. The porous barium titanate single crystal provided by the invention has an ultrahigh piezoelectric voltage coefficient which can reach (50-55) * 10 <-3 > Vm / N, and has a better application prospect in electromechanical devices such as sensors, transducers and the like. The porous barium titanate single crystal is prepared by adopting a solid phase method, seed crystals are utilized to induce single crystal growth, and the method is simple in preparation process, low in cost and beneficial to large-scale production of the porous barium titanate single crystal.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric single crystal materials technology, and in particular to a porous barium titanate single crystal, its preparation method, and its application. Background Technology

[0002] Piezoelectric materials are functional materials that enable the conversion between electrical and mechanical energy, playing a crucial role in aerospace, medical devices, and oil exploration. Based on material type, piezoelectric materials can be divided into piezoelectric single-crystal materials and piezoelectric ceramic materials. Compared to ceramic materials, piezoelectric single-crystal materials exhibit significant anisotropy in their structure, allowing for superior electrical properties through specific crystal orientations. However, commonly used piezoelectric single-crystal materials, such as barium titanate, have relatively low piezoelectric voltage coefficients, making it difficult to meet the higher performance requirements of various high-performance, high-precision instruments. Furthermore, the current preparation of piezoelectric single-crystal materials mainly relies on liquid-phase methods, including crucible lowering, Czochralski, and flux methods. These methods are costly, complex, and produce inconsistent product quality, hindering large-scale production and limiting the practical applications of piezoelectric single-crystal materials.

[0003] Therefore, how to provide a barium titanate single crystal with a higher voltage coefficient is an urgent problem to be solved in this field. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a porous barium titanate single crystal, its preparation method, and its applications. The porous barium titanate single crystal of this invention possesses an ultra-high voltage coefficient, and its preparation process is simple and low-cost.

[0005] The technical solution of the present invention is as follows:

[0006] The first aspect of this invention protects a porous barium titanate single crystal, wherein the piezoelectric voltage coefficient of the porous barium titanate single crystal is (50~55)×10⁻⁶. -3 Vm / N.

[0007] Preferably, the porous barium titanate single crystal has a porosity of 3-6% and a pore size range of 10-30 μm.

[0008] The second aspect of this invention protects a method for preparing porous barium titanate single crystals as described in the first aspect, comprising the following steps:

[0009] S1. Mix BaTiO3 and TiO2 in a certain proportion, grind, and dry to obtain powder;

[0010] S2. Add a binder to the powder, mix well, and press to obtain a blank;

[0011] S3. Place the billet in a heating device, heat it to temperature T and keep it at that temperature to remove the binder, then cold isostatically press it to obtain a dense billet.

[0012] S4. The dense blank is placed in a heating device, and a seed crystal is placed on top of the dense blank. The blank is then sintered to obtain the porous barium titanate single crystal.

[0013] Preferably, in step S1, the amount of TiO2 added is 0.3 to 0.6 mol% of the BaTiO3;

[0014] And / or, the grinding time is 20 to 24 hours;

[0015] And / or, the drying temperature is 100-120°C; the drying time is 2-3 hours.

[0016] Preferably, the amount of binder added is 2-4 wt% of the total mass of BaTiO3 and TiO2;

[0017] And / or, the adhesive comprises an aqueous solution of polyvinyl alcohol; the concentration of the aqueous solution of polyvinyl alcohol is 7-9 wt%, and the amount of polyvinyl alcohol added is 2-4 wt% of the total mass of BaTiO3 and TiO2.

[0018] Preferably, in step S2, the pressing pressure is 8-12 MPa and the pressing time is 1.0-2.0 min.

[0019] Preferably, in step S3, the heating rate is 1-2℃ / min, the temperature T is 550-650℃, and the holding time is 2-4h;

[0020] And / or, the pressure of the cold isostatic pressing is 120-150 MPa, and the time is 25-35 min.

[0021] Preferably, in step S4, the seed crystal comprises a BaTiO3 single crystal with an orientation of

[001] .

[0022] Preferably, in step S4, the sintering is performed by heating to 1430-1440°C at a rate of 1.2-1.6°C / min and holding at that temperature for 10-30 hours.

[0023] The third aspect of this invention protects the application of the porous barium titanate single crystal described in the first aspect and / or the porous barium titanate single crystal prepared by the preparation method described in the second aspect in electromechanical devices.

[0024] The beneficial technical effects of this invention are as follows:

[0025] This invention employs a solid-state method, utilizing seed crystals to induce single-crystal growth, to prepare porous barium titanate single crystals. This preparation method is simple, easy to operate, and low-cost, which is beneficial for the large-scale production of porous barium titanate single crystals. The porous barium titanate single crystals of this invention can achieve ultra-high piezoelectric voltage coefficients, showing good application prospects in electromechanical devices such as sensors and transducers. It also provides feasibility guidance for the application of environmentally friendly lead-free piezoelectric single crystals in electromechanical devices. Attached Figure Description

[0026] Figure 1 These are sample images of porous barium carbonate single crystals prepared in Examples 1, 2, and 3.

[0027] Figure 2 The image shows the SEM pattern of the porous barium carbonate single crystal obtained in Example 3.

[0028] Figure 3 The image shows the XRD pattern of the porous barium carbonate single crystal prepared in Example 3.

[0029] Figure 4 The graph shows a comparison of the dielectric properties of the porous barium carbonate single crystal prepared in Example 3 with those of Comparative Examples 1 and 2.

[0030] Figure 5 The images show the porous barium carbonate single crystal samples prepared in Comparative Examples 4-7.

[0031] Figure 6 This is a sample image of the porous barium carbonate single crystal prepared in Comparative Example 8. Detailed Implementation

[0032] A porous barium titanate single crystal, wherein the piezoelectric voltage coefficient of the porous barium titanate single crystal is (50~55)×10 -3 Vm / N.

[0033] In some embodiments, the piezoelectric voltage coefficient of the porous barium titanate single crystal is 52.62 × 10⁻⁶. -3 Vm / N.

[0034] In some embodiments, the porosity of the porous barium titanate single crystal is 3–6%; the pore size ranges from 10 to 30 μm. The pores are mainly spherical and irregularly distributed inside the porous barium titanate single crystal.

[0035] Generally, the density of barium titanate (BTO) single crystals affects the piezoelectric properties of the material; higher density results in superior piezoelectric performance and a larger piezoelectric coefficient. Therefore, the presence of porosity typically reduces the piezoelectric properties of BTO single crystals, leading to a decrease in the piezoelectric coefficient. However, the applicant's research has revealed that in this invention, the presence of porosity affects the distribution of domain structures around the porosity, disrupting the long-range order of the tetragonal ferroelectric domains and introducing a local stress field. During polarization, a portion of the contribution to piezoelectric performance changes from polarization stretching to polarization rotation, intrinsically improving piezoelectricity and neutralizing the weakening of piezoelectric performance originally caused by non-dense structure. The piezoelectric coefficient of the porous barium titanate single crystal of this invention is essentially the same as that of commercially available BTO single crystals.

[0036] It is understandable that the porous structure negatively impacts the dielectric properties of BTO single crystals, reducing their dielectric constant. Therefore, the porous barium titanate single crystal of this invention has a lower dielectric constant. According to the formula for calculating the piezoelectric voltage coefficient: g 33 =d 33 / (ε0ε 33 ), where g 33 The piezoelectric voltage coefficient (Vm / N) is represented by d. 33 ε represents the piezoelectric coefficient (m / V), and ε0 represents the vacuum permittivity, approximately 8.854 × 10⁻⁶. -12 F / m, ε 33 This represents the parallel component (dimensionless) of the dielectric constant under constant stress. The porous structure has little effect on the piezoelectric coefficient of BTO single crystals, but it significantly reduces their dielectric constant. Combined with this formula, it can be seen that porous barium titanate single crystals can achieve ultra-high piezoelectric voltage coefficients. A high piezoelectric voltage coefficient can significantly improve the voltage output efficiency of materials under mechanical stress, thereby enhancing the sensitivity and energy conversion efficiency of electromechanical devices such as sensors and transducers.

[0037] A method for preparing porous barium titanate single crystals includes the following steps:

[0038] S1. Mix BaTiO3 and TiO2 in a certain proportion, grind, and dry to obtain powder;

[0039] S2. Add a binder to the powder, mix well, and press to obtain a blank;

[0040] S3. Place the billet in a heating device, heat it to temperature T and keep it at that temperature to remove the binder, then cold isostatically press it to obtain a dense billet.

[0041] S4. The dense blank is placed in a heating device, and a seed crystal is placed on top of the dense blank. The blank is then sintered to obtain the porous barium titanate single crystal.

[0042] In some embodiments, in step S4, the sintering is performed by heating to 1430-1440°C at a rate of 1.2-1.6°C / min and holding at that temperature for 10-30 hours.

[0043] When preparing porous barium titanate single crystals using the above method, the lattice expands during heating and contracts during cooling. This change can easily lead to uneven bonding between grains and difficulty in maintaining a stable density. At the same time, without applying external pressure to compensate for this volume change, some areas will experience uneven stress during cooling, leaving voids and ultimately forming a porous structure.

[0044] The heating rate during sintering should not be too fast or too slow. If it is too fast, the grain growth rate will increase, resulting in an increase in the average grain size, making it difficult to prepare porous barium titanate single crystals. If it is too slow, the grain growth rate will be inconsistent, resulting in obviously abnormally large grains, which in turn makes the quality of BTO single crystals unstable.

[0045] The sintering temperature should not be too high or too low. If it is too high, liquefaction will occur in the material and the grain growth rate will be accelerated, resulting in a large number of abnormal grains, making it difficult to prepare porous barium titanate single crystals. It may also result in the material being made as a ceramic material. If it is too low, the material being made will also be a ceramic material rather than a single crystal material.

[0046] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0047] Example 1

[0048] A method for preparing porous barium titanate single crystals includes the following steps:

[0049] S1. Mix BaTiO3 and TiO2 at a molar ratio of 1:0.5%, grind thoroughly for 24 hours, and dry in an oven at 100℃ for 3 hours to obtain powder;

[0050] S2. Add a 7wt% polyvinyl alcohol aqueous solution to the powder, mix well, and press under a pressure of 10MPa for 1min to obtain a green body; the polyvinyl alcohol is 3wt% of the total mass of BaTiO3 and TiO2.

[0051] S3. Place the billet in a muffle furnace and heat it to 600℃ at a rate of 1℃ / min and hold it for 3 hours. Then, cold isostatically press it at 150MPa for 30 minutes to obtain a dense billet.

[0052] S4. Place the dense billet in a muffle furnace, and place a 1mm×1mm×0.2mm

[001] oriented BTO single crystal on top of the dense billet as a seed crystal to induce its single crystal growth. Heat the billet to 1440℃ at a rate of 1.5℃ / min and hold for 10h for sintering to obtain a porous barium titanate single crystal with a porosity of 5% and a pore size range of 10~30μm.

[0053] Example 2

[0054] A method for preparing porous barium titanate single crystals is basically the same as that in Example 1, except that the heat preservation time in step S4 is 20h.

[0055] Example 3

[0056] A method for preparing porous barium titanate single crystals is basically the same as that in Example 1, except that the heat preservation time in step S4 is 30h.

[0057] Comparative Example 1

[0058] A method for preparing barium titanate ceramic material is basically the same as that in Example 1, except that in step S4: no seed crystal is placed on the top of the dense green body, the sintering temperature is 1450℃, and the holding time is 3h. The rest is the same as in Example 1.

[0059] Comparative Example 2

[0060] Commercially available barium titanate single crystal material was selected and cut into the same size as the porous barium titanate single crystal in Example 1 as Comparative Example 2. The barium titanate single crystal material used in this comparative example was purchased from Hefei Kejing Materials Technology Co., Ltd.

[0061] Comparative Example 3

[0062] Commercially available PZT5 ceramic sheets were selected and cut to the same size as the porous barium titanate single crystal in Example 1 as Comparative Example 3. The PZT5 ceramic sheets used in this comparative example were purchased from Hefei Kejing Materials Technology Co., Ltd.

[0063] Comparative Example 4

[0064] A method for preparing porous barium titanate single crystals is basically the same as that in Example 1, except that the sintering temperature in step S4 is 1420℃.

[0065] Comparative Example 5

[0066] A method for preparing porous barium titanate single crystals is basically the same as that in Example 1, except that the heating rate in step S4 is 2℃ / min.

[0067] Comparative Example 6

[0068] A method for preparing porous barium titanate single crystals is basically the same as that in Example 1, except that the heating rate in step S4 is 1℃ / min.

[0069] Comparative Example 7

[0070] A method for preparing porous barium titanate single crystals is basically the same as that in Example 1, except that the sintering temperature in step S4 is 1450℃.

[0071] Comparative Example 8

[0072] A method for preparing a porous barium titanate single crystal is basically the same as that in Example 1, except that in step S4: a 1 mm × 1 mm × 0.2 mm

[110] oriented barium titanate single crystal is placed on the top of the dense blank.

[0073] Test case

[0074] Figure 1 The image shows a sample of porous barium titanate single crystals prepared in the above embodiments, combined with... Figure 1 It can be seen that the size of the porous barium titanate single crystal in Example 3 is larger than that in Examples 2 and 1; indicating that during sintering, within the range of 10 to 30 hours of holding time, the size of the porous barium titanate single crystal gradually increases with the extension of the holding time.

[0075] Figure 2 The image shows the SEM pattern of the porous barium titanate single crystal prepared in Example 3. Figure 2 It can be seen that there are no obvious grain boundaries on the surface of the porous barium titanate single crystal in Example 3, which can preliminarily prove that the material is a single crystal structure. At the same time, it can be seen that there are pore structures of different sizes in the porous barium titanate single crystal.

[0076] Figure 3 The XRD pattern of the porous barium titanate single crystal prepared in Example 3 is shown below. Figure 3 It can be seen that the porous barium titanate single crystal in Example 3 exhibits a clearly defined

[001] oriented single crystal structure.

[0077] Figure 4 This is a comparison diagram of the dielectric properties of the porous barium titanate single crystal prepared in Example 3 with those of Comparative Examples 1 and 2.

[0078] Table 1 shows the comprehensive performance data of the porous barium titanate single crystal prepared in Example 3 compared with those of Comparative Examples 1, 2, and 3.

[0079] Table 1: Overall performance data of Example 3 and Comparative Examples 1, 2, and 3

[0080]

[0081] according to Figure 4As shown in Table 1, the dielectric properties of the porous barium titanate single crystal in Example 3 are significantly lower than those of the barium titanate ceramic material in Comparative Example 1 and the commercially available barium titanate single crystal in Comparative Example 2. Table 1 also shows that the piezoelectric coefficient of the porous barium titanate single crystal in Example 3 is basically the same as that of the commercially available barium titanate single crystal in Comparative Example 2, but both are slightly smaller than those of the barium titanate ceramic material in Comparative Example 1 and also smaller than those of the commercially available PZT5 ceramic sheet in Comparative Example 3. The formula for calculating the piezoelectric coefficient is: g 33 =d 33 / (ε0ε 33 ), where, where, g 33 The piezoelectric voltage coefficient (Vm / N) is represented by d. 33 ε represents the piezoelectric coefficient (m / V), and ε0 represents the vacuum permittivity, approximately 8.854 × 10⁻⁶. -12 F / m, ε 33 The parallel component of the dielectric constant under constant stress (dimensionless) is represented. Based on the formula for the piezoelectric voltage coefficient, the piezoelectric voltage coefficients of the materials in Example 3 and Comparative Examples 1-3 can be calculated. The results are shown in Table 1. The porous barium titanate single crystal of Example 3 has a high piezoelectric voltage coefficient, far exceeding that of the barium titanate ceramic material of Example 1, the commercially available barium titanate single crystal of Example 2, and the commercially available PZT5 ceramic sheet in Comparative Example 3. This indicates that the porous barium titanate single crystal material prepared by the method of this invention can obtain an ultra-high piezoelectric voltage coefficient, and still exhibits significant advantages compared to the commercially available PZT5 ceramic material.

[0082] Figure 5 Images of porous barium titanate single crystals prepared in Comparative Examples 4–7 are shown. (Combined with...) Figure 5 It can be seen that in Comparative Example 4, the sintering temperature was too low, resulting in a ceramic material rather than a single crystal material. In Comparative Example 7, the sintering temperature was too high, making it difficult to prepare porous barium titanate single crystals. This is because the high sintering temperature caused liquefaction in the prepared material, and at the same time, the grain growth rate accelerated, resulting in a large number of abnormal grains. In Comparative Example 5, the heating rate was too fast, making it difficult to prepare porous barium titanate single crystals. This is because the excessively fast heating rate led to an accelerated grain growth rate and a significant increase in the average grain size, making it difficult to prepare single crystal materials. In Comparative Example 6, the heating rate was too slow, resulting in unstable quality of the single crystals. This is because the slow heating rate led to inconsistent grain growth rates and the appearance of obviously abnormally large grains.

[0083] Figure 6 This is a sample image of the porous barium titanate single crystal prepared in Comparative Example 8, combined with... Figure 6It can be seen that the material induced by the

[110] -oriented seed crystal is composed of multiple small single crystals with different orientations, rather than a single orientation. The reason is speculated to be that the growth direction of the single crystal induced by the

[110] -oriented seed crystal is in two directions,

[100] and

[010] . With more choices of crystal growth direction, it is easy to cause orientation disorder, resulting in the co-growth of multiple single crystals with different orientations, which makes it difficult to prepare porous barium titanate single crystals.

[0084] In summary, the method of this invention can prepare porous barium titanate single crystals. The preparation method is simple to operate and has low production cost. At the same time, the porous barium titanate single crystals can obtain ultra-high voltage coefficients.

[0085] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A porous barium titanate single crystal, characterized in that, The piezoelectric voltage coefficient of the porous barium titanate single crystal is (50~55)×10. -3 Vm / N.

2. The porous barium titanate single crystal according to claim 1, characterized in that, The porous barium titanate single crystal has a porosity of 3-6% and a pore size range of 10-30 μm.

3. A method for preparing porous barium titanate single crystals according to any one of claims 1-2, characterized in that, Includes the following steps: S1. Mix BaTiO3 and TiO2 in a certain proportion, grind, and dry to obtain powder; S2. Add a binder to the powder, mix well, and press to obtain a blank; S3. Place the billet in a heating device, heat it to temperature T and keep it at that temperature to remove the binder, then cold isostatically press it to obtain a dense billet. S4. The dense blank is placed in a heating device, and a seed crystal is placed on top of the dense blank. The blank is then sintered to obtain the porous barium titanate single crystal.

4. The preparation method according to claim 3, characterized in that, In step S1, the amount of TiO2 added is 0.3 to 0.6 mol% of the BaTiO3; And / or, the grinding time is 20 to 24 hours; And / or, the drying temperature is 100-120°C; the drying time is 2-3 hours.

5. The preparation method according to claim 3, characterized in that, In step S2, the amount of binder added is 2 to 4 wt% of the total mass of BaTiO3 and TiO2; And / or, the adhesive comprises an aqueous solution of polyvinyl alcohol; the concentration of the aqueous solution of polyvinyl alcohol is 7-9 wt%, and the amount of polyvinyl alcohol added is 2-4 wt% of the total mass of BaTiO3 and TiO2.

6. The preparation method according to claim 3, characterized in that, In step S2, the pressing pressure is 8-12 MPa, and the pressing time is 1.0-2.0 min.

7. The preparation method according to claim 3, characterized in that, In step S3, the heating rate is 1-2℃ / min, the temperature T is 550-650℃, and the holding time is 2-4h. And / or, the pressure of the cold isostatic pressing is 120-150 MPa, and the time is 25-35 min.

8. The preparation method according to claim 3, characterized in that, In step S4, the seed crystal includes a BaTiO3 single crystal with an orientation of [001].

9. The preparation method according to claim 3, characterized in that, In step S4, the sintering is carried out by heating to 1430-1440°C at a rate of 1.2-1.6°C / min and holding at that temperature for 10-30 hours.

10. The application of a porous barium titanate single crystal according to any one of claims 1-2, and / or a porous barium titanate single crystal prepared by the preparation method according to any one of claims 3-9, in electromechanical devices.

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