A high-curie temperature lead-free piezoelectric ceramic and a method for preparing the same

Abstract

This invention proposes a high Curie temperature lead-free piezoelectric ceramic and its preparation method. The formula for the lead-free piezoelectric ceramic is Ba(Hf) 0.02 Ti 0.98 The preparation method of BaCO3-xSiO2, where x = 0-1.5, includes the following steps: BaCO3, TiO2, HfO2, and SiO2 powders are weighed according to a certain ratio; the weighed powders are ball-milled for the first time, then dried and sieved; the powders are pre-fired; then ball-milled a second time; after ball milling, dried and sieved; paraffin wax is added to the powder for granulation; the granulated ceramic powder is made into ceramic green bodies; the ceramic green bodies are placed in a tube furnace for debinding and sintering to obtain lead-free piezoelectric ceramics. This invention uses Ba(HfO2-xSiO2) as the raw material. 0.02 Ti 0.98 Using BHT (Bio-O3) as the matrix, SiO2 is introduced to add a second phase, thereby increasing the Curie temperature. During the process of SiO2 entering the BHT ceramic matrix, the second phase is formed and enriched at the grain boundaries in the form of independent grains. When the temperature rises to near the Curie temperature, the second phase will hinder the transformation of the ferroelectric phase into the paraelectric phase, thereby achieving the purpose of increasing the Curie temperature.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric ceramics technology, and in particular to a high Curie temperature lead-free piezoelectric ceramic and its preparation method. Background Technology

[0002] In the information age, the discovery and application of piezoelectric materials have provided new solutions for information transmission and energy conversion, fully demonstrating the crucial role of materials science in modern technological progress. Among them, piezoelectric ceramics, as an important functional material for realizing the mutual conversion of mechanical energy and electrical energy, play an irreplaceable role in key fields such as aerospace, medical devices, precision measurement, and electronic information technology due to their unique physical properties.

[0003] In the classification of piezoelectric materials, based on their constituent elements, they are mainly divided into two categories: lead-based and lead-free piezoelectric ceramics. Lead-based piezoelectric ceramics, Pb(Zr,Ti)O3 (PZT), are currently the most widely used piezoelectric materials. However, the widespread use of lead-based piezoelectric ceramics has brought concerns about environmental pollution and human health. During high-temperature production processes, the volatilization of lead can pollute the environment. Furthermore, long-term exposure to environments with excessive lead content may lead to health risks such as damage to the nervous system, cardiovascular disease, osteoporosis, reproductive system disorders, and decreased immune function; these effects are often irreversible. With increasing public concern about environmental pollution and health, internationally, a series of laws and regulations aimed at restricting the use of lead-containing materials have begun to be formulated and implemented. Against this international backdrop, the development of lead-free piezoelectric ceramics to replace traditional lead-based piezoelectric materials is not only a necessity to address regulatory restrictions but also aligns with the scientific trend of sustainable development and environmental protection. As the world's largest industrial country and the largest exporter of industrial products, my country's exports to relevant countries will inevitably be restricted with the implementation of relevant national laws. In order to avoid such restrictions, it is urgent to develop products that can replace lead-based piezoelectric ceramics.

[0004] Chemical doping is one of the most common techniques for modifying piezoelectric ceramics. It involves altering the microstructure of the raw material by doping with ions of different radii, thereby regulating the performance of the piezoelectric ceramic. Conventional doping methods include equivalent doping and heterovalent doping, both of which introduce changes to the microstructure of the piezoelectric ceramic, thus affecting its performance. Changes in microstructure directly impact various properties of piezoelectric ceramics, such as Curie temperature and piezoelectric constant.

[0005] The Curie temperature marks the critical point at which ferroelectric or ferrielectric materials transform into paraelectric materials. In other words, the Curie temperature directly affects the operating temperature range of piezoelectric ceramics and is one of the important performance parameters of BT-based piezoelectric ceramics. The proportionality constant describing the linear response between the mechanical and electrical quantities of a piezoelectric material is called the piezoelectric constant, which is also an important performance parameter of BT-based piezoelectric ceramics. However, in traditional chemical doping methods, the Curie temperature and piezoelectric constant cannot be increased simultaneously, nor can it be guaranteed that one performance parameter will not decrease while the other is effectively improved. Summary of the Invention

[0006] To achieve the above objectives, the present invention aims to provide a lead-free piezoelectric ceramic with a high Curie temperature and a method for preparing the same, which can increase the Curie temperature of the lead-free piezoelectric ceramic without reducing the piezoelectric constant.

[0007] To achieve the above objectives, this invention proposes a high Curie temperature lead-free piezoelectric ceramic, the expression of which is Ba(Hf) 0.02 Ti 0.98 O3-xSiO2, where x = 0 to 1.5.

[0008] This invention also proposes a method for preparing lead-free piezoelectric ceramics with high Curie temperature, comprising the following steps:

[0009] S1: Weigh out BaCO3, TiO2, HfO2, and SiO2 powders according to the specified proportions;

[0010] S2: The weighed powder is ball-milled for the first time, then dried and sieved;

[0011] S3: Pre-calcine the powder, then ball mill the powder a second time, dry the ball-milled powder, and sieve it;

[0012] S4: Add paraffin wax to the sieved powder to granulate it, and then make the granulated ceramic powder into a ceramic body.

[0013] S5: The ceramic blank is placed in a tube furnace for debinding and sintering to obtain lead-free piezoelectric ceramic.

[0014] In the above scheme, the particle size of BaCO3, TiO2, HfO2, and SiO2 powders is 0.1–5 μm, and the purity is greater than 99.0%.

[0015] In the above scheme: In step S2, anhydrous ethanol is first added to the weighed powder, and then ball milling is performed for the first time to prevent the powder from sticking together.

[0016] In the above scheme, the ratio of the weighed powder to anhydrous ethanol is 1g:1.5-2ml.

[0017] In the above scheme, the ball milling parameters for the first and second ball milling are: ball milling speed 300-400 rpm / min, ball milling time 12-24h, the ball milling beads used are ZrO2 with a purity of 95%, and the ball mill contains three types of ball milling beads with diameters of 1mm, 3mm and 5mm, respectively, with a corresponding mass ratio of 1:3:5.

[0018] In the above scheme: In step S4, the mass of paraffin wax added is 6%-8% of the powder mass.

[0019] In the above scheme: in step S5, the glue discharge temperature is 600-650℃, and the holding time is 4h; solid-state sintering method is adopted, and the sintering temperature is 1300~1400℃, wherein the heating rate from room temperature to 600℃ is 5℃ / min; the heating rate from 600℃ to 1100℃ is 4℃ / min; and the heating rate from 1100℃ to 1400℃ is 3℃ / min.

[0020] The beneficial effects of this invention are: the use of Ba(Hf) 0.02 Ti 0.98 Using BHT (Bio-O3) as the matrix, a novel chemical modification method is employed, which differs from common equivalent and heterovalent doping. SiO2 is introduced to add a second phase, thereby increasing the Curie temperature. During the process of SiO2 entering the BHT ceramic matrix, the second phase formed is enriched at the grain boundaries in the form of independent grains. When the temperature rises to near the Curie temperature, the second phase enriched at the grain boundaries will hinder the transformation of the ferroelectric phase into the paraelectric phase, thereby achieving the purpose of increasing the Curie temperature. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0022] Figure 1 XRD patterns of lead-free piezoelectric ceramics. (a) XRD pattern. (b) Magnified XRD pattern.

[0023] Figure 2 SEM and EDS images of lead-free piezoelectric ceramics. (a)-(d) SEM morphology and grain size distribution of ceramics; (e) Relationship between grain size and SiO2 content; (f) Enlarged view of morphology region.

[0024] Figure 3 The dielectric temperature spectrum of lead-free piezoelectric ceramics is shown. (a)-(d)ε r -T and tanδ-T curves; (e) Schematic diagram of grain equivalent capacitor.

[0025] Figure 4 The diagram shows the test results for the ferroelectric and piezoelectric properties of lead-free piezoelectric ceramics. Detailed Implementation

[0026] like Figure 1 As shown in Figure 4, a high Curie temperature lead-free piezoelectric ceramic is described by the expression Ba(Hf) 0.02 Ti 0.98 O3-xSiO2, where x = 0 to 1.5. The specific chemical composition is shown in Table 1.

[0027] Table 1 Ba(Hf) 0.02 Ti 0.98 Chemical composition of O3-xSiO2 lead-free piezoelectric ceramics

[0028]

[0029] This invention also proposes a method for preparing lead-free piezoelectric ceramics with high Curie temperature, which mainly consists of the following steps:

[0030] S1: Weigh out BaCO3, TiO2, HfO2, and SiO2 powders according to the specified proportions. The powder particle size is 0.1–5 μm, and the purity of each powder is greater than 99.0%.

[0031] S2: Perform the first ball milling on the weighed powder. Add anhydrous ethanol before ball milling to prevent the powder from sticking together. The ratio of the weighed powder to anhydrous ethanol is 1g:1.5-2ml. After ball milling, dry and sieve.

[0032] S3: Pre-calcine the powder, then ball-mill the powder a second time, and dry and sieve the ball-milled powder.

[0033] The ball milling parameters for the first and second ball millings are as follows: ball milling speed 300-400 rpm / min, ball milling time 12-24 h, the ball milling beads used are 95% pure ZrO2, and the ball mill contains three diameter ball milling beads, namely 1 mm, 3 mm and 5 mm, with a corresponding mass ratio of 1:3:5.

[0034] S4: Add paraffin wax to the sieved powder to granulate. The mass of the added paraffin wax is 6%-8% of the powder mass. Make the granulated ceramic powder into ceramic blanks.

[0035] S5: The ceramic blank is placed in a tube furnace for debinding and sintering to obtain lead-free piezoelectric ceramics; the debinding temperature is 600-650℃, and the holding time is 4h; solid-state sintering method is adopted, and the sintering temperature is 1300~1400℃, wherein the heating rate from room temperature to 600℃ is 5℃ / min; the heating rate from 600℃ to 1100℃ is 4℃ / min; and the heating rate from 1100℃ to 1400℃ is 3℃ / min.

[0036] Example 1

[0037] S1: According to Ba(Hf) 0.02 Ti 0.98 BaCO3, TiO2, HfO2, and SiO2 powders were weighed, with each powder having a particle size of 0.1–5 μm and a purity greater than 99.0%.

[0038] S2: Transfer the weighed powder to a nylon ball mill jar for the first ball milling. Add anhydrous ethanol before milling to prevent powder adhesion. The ratio of weighed powder to anhydrous ethanol is 90 ml of anhydrous ethanol per 50 g of ceramic powder. The milling parameters are: milling speed 300 rpm / min, milling time 12 h, and the milling beads used are 95% pure ZrO2. The mill contains three diameter milling beads: 1 mm, 3 mm, and 5 mm, with a corresponding mass ratio of 1:3:5. Transfer the milled powder to an oven and dry at 60℃ for 10 h. After drying, separate the ceramic powder from the milling beads using an 80-mesh standard sieve.

[0039] S3: Place the powder in an alumina crucible for pre-firing at 1200℃ for 3 hours. After pre-firing, ball mill the powder a second time, dry and sieve the milled powder, following the same details as the first ball milling.

[0040] S4: Add paraffin wax to the sieved powder to granulate. The mass of the added paraffin wax is 6% of the mass of the powder. Compress the granulated ceramic powder into round ceramic blanks with a diameter of 1.2 mm and a diameter of 1.1 mm under a pressure of 30 MPa.

[0041] S5: The ceramic blank is placed in a tube furnace for debinding and sintering to obtain lead-free piezoelectric ceramics; the debinding temperature is 600℃ and the holding time is 4h; solid-state sintering method is adopted, and the sintering temperature is 1300~1400℃, wherein the heating rate from room temperature to 600℃ is 5℃ / min; the heating rate from 600℃ to 1100℃ is 4℃ / min; and the heating rate from 1100℃ to 1400℃ is 3℃ / min, thus obtaining the final ceramic sample.

[0042] S6: Finally, according to the test requirements, silver paste is coated on both poles of the ceramic sample and then fired into silver.

[0043] Example 2

[0044] S1: According to Ba(Hf) 0.02 Ti 0.98 BaCO3, TiO2, HfO2, and SiO2 powders were weighed, with each powder having a particle size of 0.1–5 μm and a purity greater than 99.0%.

[0045] S2: Transfer the weighed powder to a nylon ball mill jar for the first ball milling. Add anhydrous ethanol before milling to prevent powder adhesion. The ratio of weighed powder to anhydrous ethanol is 90 ml of anhydrous ethanol per 50 g of ceramic powder. The milling parameters are: milling speed 300 rpm / min, milling time 12 h, and the milling beads used are 95% pure ZrO2. The mill contains three diameter milling beads: 1 mm, 3 mm, and 5 mm, with a corresponding mass ratio of 1:3:5. Transfer the milled powder to an oven and dry at 60℃ for 10 h. After drying, separate the ceramic powder from the milling beads using an 80-mesh standard sieve.

[0046] S3: Place the powder in an alumina crucible for pre-firing at 1200℃ for 3 hours. After pre-firing, the powder is ball-milled a second time. The ball-milled powder is then dried and sieved, following the same procedures as the first ball milling.

[0047] S4: Add paraffin wax to the sieved powder to granulate. The mass of the added paraffin wax is 6% of the mass of the powder. Compress the granulated ceramic powder into round ceramic blanks with a diameter of 1.2 mm and a diameter of 1.1 mm under a pressure of 30 MPa.

[0048] S5: The ceramic blank is placed in a tube furnace for debinding and sintering to obtain lead-free piezoelectric ceramics; the debinding temperature is 600℃ and the holding time is 4h; solid-state sintering method is adopted, and the sintering temperature is 1300~1400℃, wherein the heating rate from room temperature to 600℃ is 5℃ / min; the heating rate from 600℃ to 1100℃ is 4℃ / min; and the heating rate from 1100℃ to 1400℃ is 3℃ / min, thus obtaining the final ceramic sample.

[0049] S6: Finally, according to the test requirements, silver paste is coated on both poles of the ceramic sample and then fired into silver.

[0050] Example 3

[0051] S1: According to Ba(Hf) 0.02 Ti 0.98 BaCO3, TiO2, HfO2, and SiO2 powders were weighed, with each powder having a particle size of 0.1–5 μm and a purity greater than 99.0%.

[0052] S2: Transfer the weighed powder to a nylon ball mill jar for the first ball milling. Add anhydrous ethanol before milling to prevent powder adhesion. The ratio of weighed powder to anhydrous ethanol is 90 ml of anhydrous ethanol per 50 g of ceramic powder. The milling parameters are: milling speed 300 rpm / min, milling time 12 h, and the milling beads used are 95% pure ZrO2. The mill contains three diameter milling beads: 1 mm, 3 mm, and 5 mm, with a corresponding mass ratio of 1:3:5. Transfer the milled powder to an oven and dry at 60℃ for 10 h. After drying, separate the ceramic powder from the milling beads using an 80-mesh standard sieve.

[0053] S3: Place the powder in an alumina crucible for pre-firing at 1200℃ for 3 hours. After pre-firing, the powder is ball-milled a second time. The ball-milled powder is then dried and sieved, following the same procedures as the first ball milling.

[0054] S4: Add paraffin wax to the sieved powder to granulate. The mass of the added paraffin wax is 6% of the mass of the powder. Compress the granulated ceramic powder into round ceramic blanks with a diameter of 1.2 mm and a diameter of 1.1 mm under a pressure of 30 MPa.

[0055] S5: The ceramic blank is placed in a tube furnace for debinding and sintering to obtain lead-free piezoelectric ceramics; the debinding temperature is 600℃ and the holding time is 4h; solid-state sintering method is adopted, and the sintering temperature is 1300~1400℃, wherein the heating rate from room temperature to 600℃ is 5℃ / min; the heating rate from 600℃ to 1100℃ is 4℃ / min; and the heating rate from 1100℃ to 1400℃ is 3℃ / min, thus obtaining the final ceramic sample.

[0056] S6: Finally, according to the test requirements, silver paste is coated on both poles of the ceramic sample and then fired into silver.

[0057] Example 4

[0058] S1: According to Ba(Hf) 0.02 Ti 0.98 )O3-xSiO2, x=1.5 Weigh out BaCO3, TiO2, HfO2 and SiO2 powders, each powder has a particle size of 0.1~5μm and a purity of greater than 99.0%.

[0059] S2: Transfer the weighed powder to a nylon ball mill jar for the first ball milling. Add anhydrous ethanol before milling to prevent powder adhesion. The ratio of weighed powder to anhydrous ethanol is 90 ml of anhydrous ethanol per 50 g of ceramic powder. The milling parameters are: milling speed 300 rpm / min, milling time 12 h, and the milling beads used are 95% pure ZrO2. The mill contains three diameter milling beads: 1 mm, 3 mm, and 5 mm, with a corresponding mass ratio of 1:3:5. Transfer the milled powder to an oven and dry at 60℃ for 10 h. After drying, separate the ceramic powder from the milling beads using an 80-mesh standard sieve.

[0060] S3: Place the powder in an alumina crucible for pre-firing at 1200℃ for 3 hours. After pre-firing, the powder is ball-milled a second time. The ball-milled powder is then dried and sieved, following the same procedures as the first ball milling.

[0061] S4: Add paraffin wax to the sieved powder to granulate. The mass of the added paraffin wax is 6% of the mass of the powder. Compress the granulated ceramic powder into round ceramic blanks with a diameter of 1.2 mm and a diameter of 1.1 mm under a pressure of 30 MPa.

[0062] S5: The ceramic blank is placed in a tube furnace for debinding and sintering to obtain lead-free piezoelectric ceramics; the debinding temperature is 600℃ and the holding time is 4h; solid-state sintering method is adopted, and the sintering temperature is 1300~1400℃, wherein the heating rate from room temperature to 600℃ is 5℃ / min; the heating rate from 600℃ to 1100℃ is 4℃ / min; and the heating rate from 1100℃ to 1400℃ is 3℃ / min, thus obtaining the final ceramic sample.

[0063] S6: Finally, according to the test requirements, silver paste is coated on both poles of the ceramic sample and then fired into silver.

[0064] Figure 1 XRD patterns of lead-free piezoelectric ceramics. (a) XRD pattern. (b) Magnified XRD pattern. Second phase was detected in all samples with x = 0.5-1.5 wt%. By comparing with standard cards, the second phase was found to be Ba2TiSi2O8 and Ba2SiO8, both of which are Si-containing oxides. Comparing the diffraction peaks of the standard cards, the 45° characteristic peak of x = 0 wt% split into obvious T(002) and O(022), O(200) diffraction peaks, indicating that the two phases O and T coexist at room temperature.

[0065] Figure 2 SEM and EDS of lead-free piezoelectric ceramics; (a)-(d) SEM morphology and grain size distribution of ceramics; (e) Relationship between grain size and SiO2 content; (f) Enlarged view of morphology region; Figure 2In (a)-(e), it was observed that the grain size was relatively large (30.33 μm) when x = 0 w%, but immediately decreased to 0.6 μm upon the addition of SiO2. With increasing SiO2 content, the grain size increased again. This is because the increase in the second phase during sintering led to an increase in the liquid phase, thus slightly increasing the grain size. The influence of the liquid phase and the effect of the second phase as a grain growth inhibitor coexisted. Through analysis of... Figure 2 EDS elemental analysis of the three points in (f) shows that the second phase enriched with Si is embedded inside the BHT ceramic grains.

[0066] Figure 3 Dielectric temperature spectrum testing for lead-free piezoelectric ceramics. (a)-(d)ε r -T and tanδ-T curves; (e) Schematic diagram of grain equivalent capacitor; Figure 3 From (a)-(d), it can be seen that in T C Nearby ε r The -T curves show a clear gradual change from sharp and narrow to rounded and divergent as the second phase increases, indicating that the dispersion phase transition behavior of the sample increases with the increase of the second phase. Figure 3 T can be observed in (d). C Compared to (a), it increased by 14 degrees, proving that the Curie temperature can be increased by this method; as shown in Figure 3(e), with a fixed electric field E, ε r It decreases as the grain size increases.

[0067] Figure 4 For testing the ferroelectric and piezoelectric properties of lead-free piezoelectric ceramics, specifically the content of the second phase (Ba2TiSi2O8) and the Curie temperature T... C and piezoelectric constant d 33 The curve as x changes. For example... Figure 4 As shown, d can be found 33 It first decreases rapidly in the range from x = 0w% to x = 0.5w%, then d 33 The decrease in T is very slight, almost negligible. C The trend of change is exactly the opposite, slowly increasing from x = 0w% to x = 0.5w%, followed by T C It rapidly increased to 134.7℃.

Claims

1. A high Curie temperature lead-free piezoelectric ceramic, characterized in that: The expression for the lead-free piezoelectric ceramic is Ba(Hf) 0.02 Ti 0.98 O3-xSiO2, where x = 0.5~1.5wt%.

2. A method for preparing a high Curie temperature lead-free piezoelectric ceramic according to claim 1, characterized in that, Includes the following steps: S1: Weigh out BaCO3, TiO2, HfO2, and SiO2 powders according to the specified proportions; the particle size of BaCO3, TiO2, HfO2, and SiO2 powders is 0.1~5μm, and the purity of each is greater than 99.0%. S2: The weighed powder is ball-milled for the first time, then dried and sieved; S3: Pre-calcine the powder, then ball mill the powder a second time, dry the ball-milled powder, and sieve it; S4: Add paraffin wax to the sieved powder to granulate it, and then make the granulated ceramic powder into a ceramic body. S5: The ceramic blank is placed in a tube furnace for debinding and sintering to obtain lead-free piezoelectric ceramics; the debinding temperature is 600-650℃, and the holding time is 4h; solid-state sintering method is adopted, and the sintering temperature is 1300~1400℃, of which the heating rate from room temperature to 600℃ is 5℃ / min; the heating rate from 600℃ to 1100℃ is 4℃ / min; and the heating rate from 1100℃ to 1400℃ is 3℃ / min.

3. The method for preparing high Curie temperature lead-free piezoelectric ceramics according to claim 2, characterized in that: In step S2, anhydrous ethanol is first added to the weighed powder, and then the first ball milling is performed.

4. The method for preparing high Curie temperature lead-free piezoelectric ceramics according to claim 3, characterized in that: The ratio of the weighed powder to anhydrous ethanol is 1g:1.5-2ml.

5. The method for preparing high Curie temperature lead-free piezoelectric ceramics according to claim 3, characterized in that, The ball milling parameters for the first and second ball millings are as follows: ball milling speed 300-400 rpm, ball milling time 12-24 h, the ball milling beads used are 95% pure ZrO2, and the ball mill contains three types of ball milling beads with diameters of 1 mm, 3 mm and 5 mm, with a corresponding mass ratio of 1:3:

5.

6. The method for preparing high Curie temperature lead-free piezoelectric ceramics according to claim 2, characterized in that: In step S4, the mass of paraffin wax added is 6%-8% of the powder mass.

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