Defect dipole concentration gradient induced large field deformation lead-free piezoelectric ceramic material as well as preparation method and application thereof

Abstract

The invention discloses a defect dipole concentration gradient induced large field deformation lead-free piezoelectric ceramic material and a preparation method and application thereof, the defect dipole concentration gradient induced large field deformation lead-free piezoelectric ceramic material comprises single-component gradient lead-free piezoelectric ceramic with the general formula of (NayKzSr1-y-z) Nb (1-x) MxO3 and / or multi-component gradient lead-free piezoelectric ceramic with the general formula of BamTiO3, M is selected from Nb, Zr, Sn or Sb, the value range of x is 0-0.03, the value range of y is 0.45-0.55, and the value range of z is 0-0.05. The value range of z is 0.45 to 0.55; the value range of m is 0.98 to 1. The large-field-induced-deformation lead-free piezoelectric ceramic material can generate large bending deformation in an electric field, has excellent electrostrictive displacement performance, has the advantages of large equivalent electrostrictive strain, low driving electric field, good fatigue resistance, wide use temperature range, good frequency stability and the like, can generate huge output displacement after being prepared into a bicrystal structure, and has good application prospects. The method can be used for a piezoelectric actuator or a piezoelectric sensor.

Description

Technical Field

[0001] The present invention belongs to the field of piezoelectric ceramic materials, and in particular relates to a large field-induced deformation lead-free piezoelectric ceramic material induced by a defect dipole concentration gradient, and a preparation method and application thereof. Background Art

[0002] Piezoelectric actuators, capable of converting electrical energy into mechanical energy, are used in a variety of precision positioning, control, and actuation applications, playing a vital role in both industrial production and everyday life. Commercially available modified lead zirconate titanate ceramic materials can produce strains approaching 0.2% under a driving electric field of 20 kV / cm, with an equivalent inverse piezoelectric coefficient of 1000 pm / V. Therefore, the current piezoelectric actuator market is dominated by lead-based lead zirconate titanate and its modified ceramic materials. However, due to the environmental and human hazards of lead, the development of lead-free, high-performance piezoelectric ceramics has become a mainstream research direction in the field of piezoelectric actuators.

[0003] Lead-free ferroelectric material K 0.5 Na 0.5 NbO3 (abbreviated as KNN) and BaTiO3 (abbreviated as BT), as perovskite-type ferroelectric materials, not only possess excellent ferroelectricity and piezoelectricity, but also have low coercive fields (BT less than 5kV / cm, KNN less than 10kV / cm), require very low drive voltages, and can be prepared through traditional solid-phase sintering methods. However, most KNN and BT ceramics can only achieve an electrostrain of 0.1% to 0.2% at an electric field of 40kV / cm, which cannot meet the requirements of commercial piezoelectric actuators.

[0004] Through defect control engineering, field-induced strain comparable to that of lead zirconate titanate can be obtained in lead-free piezoelectric ceramics. y K z Li 1-y-z )NbO3-xSr(Nb 1-m Ni m )O3 can generate a high electrostrain of 0.25% under an electric field of 20 kV / cm, surpassing commercial lead-based lead zirconate titanate ceramics. However, the strain generated by lattice stretching has an upper limit, which has led to a bottleneck in the electrostrain of lead-free piezoelectric ceramics. Faced with the mature industrial production lines of lead-based piezoelectric ceramics, lead-free piezoelectric ceramics have difficulty gaining a significant advantage over lead-based piezoelectric ceramics. Therefore, new methods are needed to improve the field-induced displacement performance of lead-free piezoelectric ceramics to enhance their commercial value and promote the development of lead-free piezoelectric actuators. Summary of the Invention

[0005] In view of the limitations of the prior art described above, the main purpose of the present invention is to provide a lead-free piezoelectric ceramic material with large field-induced deformation induced by a defect dipole concentration gradient, so as to break through the bottleneck of the electrostrain performance of lead-free piezoelectric ceramic materials in the prior art.

[0006] Another object of the present invention is to provide an application of the large field-induced deformation lead-free piezoelectric ceramic material induced by the defect dipole concentration gradient in a piezoelectric actuator.

[0007] To achieve the above object, the present invention is implemented through the following technical solutions:

[0008] The present invention provides a large field-induced deformation lead-free piezoelectric ceramic material induced by a defect dipole concentration gradient, which includes a single-component gradient lead-free piezoelectric ceramic and / or a multi-component gradient lead-free piezoelectric ceramic; the general formula of the single-component gradient lead-free piezoelectric ceramic is (Na y K z Sr 1-y-z )Nb 1-x M x O3, M is a transition metal element selected from Nb, Zr, Sn, and Sb, the value of x ranges from 0 to 0.03, the value of y ranges from 0.45 to 0.55, and the value of z ranges from 0.45 to 0.55;

[0009] The multi-component gradient lead-free piezoelectric ceramic is composed of multiple layers of lead-free piezoelectric ceramics with different components, and its general formula is Ba m TiO3, the value range of m is 0.98~1.

[0010] Preferably, M is Sn or Sb, and the value of x ranges from 0.01 to 0.02.

[0011] More preferably, the chemical formula of the single component gradient lead-free piezoelectric ceramic is (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 M 0.01 O3, M is selected from Nb, Zr, Sn or Sb.

[0012] More preferably, the multi-component composition gradient lead-free piezoelectric ceramic is composed of Ba 0.99 It is composed of TiO3 and BaTiO3.

[0013] Preferably, the value range of m is 0.99-1.

[0014] Preferably, the crystal structure of the large field-induced deformation lead-free piezoelectric ceramic material induced by the defect dipole concentration gradient is a perovskite structure.

[0015] Preferably, the single-component composition-gradient lead-free piezoelectric ceramic obtains a composition gradient by controlling the volatilization of alkali metals during sintering, and the preparation method comprises the following steps:

[0016] 1) According to the general formula (Na y K z Sr 1-y-z )Nb 1-x M x O3 selects multiple types of potassium carbonate, sodium carbonate, strontium carbonate, niobium pentoxide, zirconium dioxide, tin dioxide and antimony pentoxide as raw materials for batching;

[0017] 2) adding anhydrous ethanol as a ball milling medium for ball milling, and drying after ball milling to obtain a mixed dry powder;

[0018] 3) pre-calcining the mixed dry powder at 800-900° C. to form a powder, adding 2 wt % to 8 wt % of a polyvinyl alcohol aqueous solution to the powder to form granules, thereby obtaining a powder;

[0019] 4) Pressing the powder into a green body, debinding at 550°C, and then sintering at 1150-1200°C to obtain a ceramic sheet;

[0020] 5) The ceramic wafer is polished, coated with silver electrodes, and then polarized in silicone oil.

[0021] More preferably, in step 3), the mass ratio of the polyvinyl alcohol aqueous solution to the powder is 0.05 to 0.1:1.

[0022] More preferably, in step 4), the pressing pressure for the green body is 180-220 MPa, the debinding treatment time is 3-5 h, the sintering treatment time is not less than 6 h, and the crucible cover for sintering is a zirconia ceramic plate with a porosity of 20%.

[0023] More preferably, in step 5), the polarization temperature is 100-150° C., the polarization electric field strength is 3-5 kV / mm, and the polarization time is 5-30 min.

[0024] Preferably, the method for preparing the multi-component composition gradient lead-free piezoelectric ceramic comprises the following steps:

[0025] a) According to the general formula Ba m TiO3 uses barium carbonate and titanium dioxide as raw materials for batching;

[0026] b) adding anhydrous ethanol as a ball milling medium for ball milling, and drying after ball milling to obtain a mixed dry powder;

[0027] c) pre-calcining the mixed dry powder at 800-900°C to form a powder, and sieving it through a sieve to obtain a fine powder;

[0028] d) adding a binder, a dispersant, a defoaming agent and an organic solvent to the fine powder and stirring and mixing them to form a slurry, vacuum defoaming the slurry and then performing tape casting to obtain a film tape;

[0029] e) laminating the membrane strips of different components into a green body according to a concentration gradient, performing a binder removal treatment at 600° C., and then sintering at 1350° C. to obtain a ceramic sheet;

[0030] f) The ceramic wafer is polished, coated with silver electrodes, and then polarized in silicone oil.

[0031] More preferably, in step c), the sieve is a 40-mesh sieve.

[0032] More preferably, in step d), the binder is polyvinyl butyral 30 and 60, the dispersant is dioctyl phthalate, the defoaming agent is n-butanol, and the organic solvent is anhydrous ethanol and n-butyl acetate.

[0033] More preferably, in step e), the lamination pressure is 180-220 MPa, the lamination temperature is 55-60° C., and the debinding treatment time is 20 hours of heating followed by 10 hours of heat preservation.

[0034] More preferably, in step f), the polarization temperature is 120-140° C., the polarization electric field strength is 2-4 kV / mm, and the polarization time is 5-30 min.

[0035] The present invention also provides application of the large field-induced deformation lead-free piezoelectric ceramic material induced by the defect dipole concentration gradient in piezoelectric elements.

[0036] Preferably, the piezoelectric element includes a single-layer ceramic piezoelectric driver, a multi-layer ceramic piezoelectric driver, a piezoelectric sensor, a piezoelectric motor, a piezoelectric vibration device or a piezoelectric ejection device.

[0037] The present invention also provides a bimorph piezoelectric element, comprising:

[0038] upper piezoelectric layer;

[0039] a conductive metal intermediate layer;

[0040] lower piezoelectric layer;

[0041] Wherein, at least one of the piezoelectric layers comprises the large field-induced deformation lead-free piezoelectric ceramic material induced by the defect dipole concentration gradient.

[0042] The piezoelectric element in this invention can achieve an equivalent strain of 1% at an electric field of 20kV / cm, twice that of commercial lead zirconate titanate, while also exhibiting excellent frequency stability, fatigue stability, and temperature stability. Assembled into a bimorph structure with a nickel metal sheet, it can achieve a vibration displacement of ±750μm at the resonant frequency in a 300V AC electric field, realizing field-induced displacement driving.

[0043] Compared to existing technologies, this invention leverages the bending deformation induced by concentration gradients, combining it with the strong coupling between defect dipoles and ferroelectric domains. This allows for ultra-high field-induced displacement performance in potassium sodium niobate ceramics through simple solid-phase sintering by volatilization of alkali metals, and also achieves significant field-induced displacement in barium titanate systems through tape casting by actively designing concentration gradients. Compared to existing lead-containing piezoelectric actuators, this lead-free piezoelectric actuator is environmentally friendly and boasts high field-induced displacement, effectively reducing the hazards posed by lead and its compounds during production, use, and disposal. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 (a) and Figure 1 (b) is (Na prepared in Example 1-5 0.49 K 0.49 Sr 0.02 )Nb 0.99 M 0.01 O3 (M is Nb, Sn, Sb or Zr) and Ba 0.99 Polarization intensity-electric field (PE) curve of TiO3 / BaTiO3 concentration gradient piezoelectric ceramics.

[0045] Figure 2 (a) and Figure 2 (b) is (Na prepared in Example 1-5 0.49 K 0.49 Sr 0.02 )Nb 0.99 M 0.01 O3 (M is Nb, Sn, Sb or Zr) piezoelectric ceramics and Ba 0.99 Bipolar equivalent strain-electric field (SE) curves of TiO3 / BaTiO3 concentration gradient piezoelectric ceramics.

[0046] Figure 3 (a) and Figure 3 (b) is (Na prepared in Example 1-5 0.49 K 0.49 Sr 0.02 )Nb 0.99 M 0.01 O3 (M is Nb, Sn, Sb or Zr) piezoelectric ceramics and Ba 0.99Unipolar equivalent strain-electric field (SE) curves of TiO3 / BaTiO3 concentration gradient piezoelectric ceramics.

[0047] Figure 4 (a) and Figure 4 (b) is prepared in Examples 2 and 5 (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sn 0.01 O3 piezoelectric ceramics and Ba 0.99 Vibration deformation of TiO3 / BaTiO3 concentration gradient piezoelectric ceramics.

[0048] Figure 5 is prepared in Example 2 (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sn 0.01 Unipolar equivalent strain-electric field curve fatigue performance test results of O3 piezoelectric ceramics at room temperature.

[0049] Figure 6 is prepared in Example 2 (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sn 0.01 The test results of the unipolar equivalent strain-electric field curve of O3 piezoelectric ceramics in the range of room temperature to 200℃.

[0050] Figure 7 (a) and Figure 7 (b) are respectively (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sn 0.01 Test results of bipolar equivalent strain-electric field curve and unipolar equivalent strain-electric field curve of O3 piezoelectric ceramics from 0.1Hz to 10Hz at room temperature.

[0051] Figure 8 is prepared in Example 2 (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sn 0.01 Displacement output performance test results of O3 piezoelectric ceramics assembled into a bimorph structure. DETAILED DESCRIPTION

[0052] To make the technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] Example 1

[0054] Preparation ingredients are (Na 0.49 K 0.49 Sr 0.02 )NbO3 (abbreviated as KNSN) based piezoelectric ceramics and testing their electrical properties. The preparation method includes the following steps:

[0055] The first step, according to the general formula (Na 0.49 K 0.49 Sr 0.02 )NbO3 Weigh high-purity (purity not less than 98%) Na2CO3, K2CO3, Nb2O5, and SrCO3 powders and ball-mill them in anhydrous ethanol for 24 h;

[0056] The second step is to dry the dispersion obtained in the first step, and calcine the obtained powder in air at 850 ° C for 6 hours;

[0057] Step 3: ball mill the powder obtained in step 2 in anhydrous ethanol medium for 24 hours;

[0058] The fourth step is to dry the dispersion obtained in the third step, cold-press the obtained powder, and sinter it at 1185° C. in air for 8 hours. During sintering, the porosity of the crucible cover is controlled to be 20% to promote the volatilization of the alkali metal.

[0059] Example 2

[0060] Preparation ingredients are (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sn 0.01 The preparation method of potassium sodium niobate-based piezoelectric ceramics of this embodiment is roughly the same as that of embodiment 1. The only difference is that in the first step, according to (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sn 0.01 The chemical formula of O3 is used to weigh the raw materials, and SnO2 raw materials need to be added.

[0061] Example 3

[0062] Preparation ingredients are (Na0.49 K 0.49 Sr 0.02 )Nb 0.99 Zr 0.01 The preparation method of the potassium sodium niobate-based piezoelectric ceramic of this embodiment is roughly the same as that of embodiment 1. The only difference is that in the first step, the (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Zr 0.01 The chemical formula of O3 is used to weigh the raw materials, and ZrO2 raw materials need to be added.

[0063] Example 4

[0064] Preparation ingredients are (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sb 0.01 The preparation method of this embodiment is similar to that of embodiment 1. The only difference is that in the first step, the potassium sodium niobate-based piezoelectric ceramic of (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 Sb 0.01 The chemical formula of O3 is used to weigh the raw materials, and Sb2O3 raw materials need to be added.

[0065] Example 5

[0066] Prepared by Ba 0.99 The concentration gradient BT-based ceramics (abbreviated as BT-G) composed of TiO3 and BaTiO3 were prepared and their electrical properties were tested. The preparation method includes the following steps:

[0067] The first step is to follow the general formula Ba 0.99 TiO3 and BaTiO3 are prepared by selecting barium carbonate and titanium dioxide as raw materials;

[0068] The second step is to add anhydrous ethanol as a ball milling medium for ball milling, and then dry the ball milling to obtain a mixed dry powder;

[0069] The third step is to pre-sinter the mixed dry powder at 900°C to form a powder, and sieve the powder with a 40-mesh sieve to obtain a fine powder;

[0070] Step 4: Add 2g of polyvinyl butyral 30 and 60 (1:2), 0.6g of dioctyl phthalate, 0.2g of n-butanol, 4g and 9.2g of n-butyl acetate to 20g of fine powder and stir to mix evenly into a slurry. After vacuum degassing, the slurry is tape-cast to obtain a 50μm thick film tape.

[0071] 5) Stack 5 layers of Ba 0.99 TiO3 film tapes and 5 layers of BaTiO3 film tapes are laminated into a green body according to a concentration gradient, debinded at 600 °C, and then sintered at 1350 °C to obtain a ceramic chip.

[0072] The following will illustrate the effects achievable by the above embodiments in combination with specific experiments.

[0073] 1. Electrical property test

[0074] Test method: Grind the piezoelectric ceramic chips prepared in Examples 1-5 to about 0.5 mm thick, silver both sides, and polarize at 120 °C and 30 kV / cm electric field for 10 min. Using an aixACCT TF1000 ferroelectric property tester, under a bipolar or unipolar triangular wave excitation of 20 kV / cm and 10 Hz, test the equivalent strain (displacement / thickness)-electric field (S-E) curve of the piezoelectric ceramic. During the test, the sample is immersed in silicone oil.

[0075] As Figure 1 shown, it can be seen from the P-E curve that as the M element changes from low electronegativity Zr to high electronegativity Sb (electronegativity Zr < Nb < Sn < Sb), the remanent polarization intensity and maximum polarization intensity of the piezoelectric ceramic gradually decrease, and the coercive field also gradually decreases, reflecting that the increased disorder makes domain deflection easier. An internal deviation of -1.88 kV / cm is observed in the P-E loop of the BT-G ceramic, confirming the existence of defect dipoles.

[0076] As Figure 2 shown, as the electronegativity of the M element increases, the maximum equivalent strain of the piezoelectric ceramic gradually increases, reaching the highest value of about 1% when M is Sb. At the same time, the asymmetry of the S-E curve also reaches the highest when M is Sb, while when M is Zr, it is close to the common "butterfly curve" of ordinary piezoelectric ceramics. Similarly, a similar asymmetric large equivalent strain curve is also observed in the BT-G ceramic, and the peak value of the equivalent strain is 0.5%.

[0077] As Figure 3 shown, as the electronegativity of the M element increases, the maximum equivalent strain of the piezoelectric ceramic gradually increases, reaching the highest value of about 0.5% when M is Sb. A relatively high equivalent strain is also observed in the BT-G ceramic, which can reach 0.28%.

[0078] The specific test results of each example are as follows:

[0079] The electrical properties of the piezoelectric ceramic prepared in Example 1 are: in the P-E curve, the remanent polarization intensity is about 15.02 μC / cm 2, with a coercive field of approximately 10.01 kV / cm. By defining the strain value at zero field in the SE curve as 0, the maximum equivalent strain is measured to be approximately 0.56% under bipolar excitation at 20 kV / cm and approximately 0.25% under unipolar excitation. The quotient Smax / Emax, the maximum equivalent strain and the maximum electric field strength, used to evaluate the electrodisplacement output performance, is approximately 2800 pm / V under bipolar excitation and approximately 1250 pm / V under unipolar excitation.

[0080] The electrical properties of the piezoelectric ceramic prepared in Example 2 are as follows: in the PE curve, the residual polarization intensity is about 15.02μC / cm 2 , with a coercive field of approximately 10.01 kV / cm. By defining the strain value at zero field in the SE curve as 0, the maximum equivalent strain is measured to be approximately 0.56% under bipolar excitation at 20 kV / cm and approximately 0.25% under unipolar excitation. The quotient Smax / Emax, the maximum equivalent strain and the maximum electric field strength, used to evaluate the electrodisplacement output performance, is approximately 2800 pm / V under bipolar excitation and approximately 1250 pm / V under unipolar excitation.

[0081] The electrical properties of the piezoelectric ceramic prepared in Example 3 are as follows: in the PE curve, the residual polarization intensity is about 22.25 μC / cm 2 , with a coercive field of approximately 14.2 kV / cm. By defining the strain value at zero field in the SE curve as 0, the maximum equivalent strain measured is approximately 0.28% under bipolar excitation at 20 kV / cm, and approximately 0.24% under unipolar excitation. The quotient Smax / Emax, the maximum equivalent strain and the maximum electric field strength, used to evaluate the electrodisplacement output performance, is approximately 1400 pm / V under bipolar excitation and approximately 1200 pm / V under unipolar excitation.

[0082] The electrical properties of the piezoelectric ceramic prepared in Example 4 are as follows: in the PE curve, the residual polarization intensity is about 9.89 μC / cm 2 , with a coercive field of approximately 6.99 kV / cm. By defining the strain value at zero field in the SE curve as 0, the maximum equivalent strain measured is approximately 1.04% under bipolar excitation at 20 kV / cm, and approximately 0.5% under unipolar excitation. The quotient Smax / Emax, the maximum equivalent strain and the maximum electric field strength, used to evaluate the electrodisplacement output performance, is approximately 5200 pm / V under bipolar excitation and approximately 2500 pm / V under unipolar excitation.

[0083] The electrical properties of the piezoelectric ceramic prepared in Example 5 are as follows: in the PE curve, the residual polarization intensity is about 15.02 μC / cm 2, with a coercive field of approximately 10.01 kV / cm. By defining the strain value at zero field in the SE curve as 0, the maximum equivalent strain is measured to be approximately 0.56% under bipolar excitation at 20 kV / cm and approximately 0.25% under unipolar excitation. The quotient Smax / Emax, the maximum equivalent strain and the maximum electric field strength, used to evaluate the electrodisplacement output performance, is approximately 2800 pm / V under bipolar excitation and approximately 1250 pm / V under unipolar excitation.

[0084] 2. Electrodeformation test

[0085] Taking the single-component concentration gradient ceramic prepared in Example 2 and the multi-component concentration gradient ceramic prepared in Example 5 as examples, a Doppler laser scanning vibrometer was used to perform vibration modal surface scanning tests under AC excitation of ±750V1Hz.

[0086] Figure 4 (a) is the vibration deformation test result of KNSN-Sn. It can be seen that the sample undergoes obvious bending deformation under a 1Hz±750V AC electric field. The amplitude of the displacement difference can reach 10μm, and the equivalent strain reaches 2%.

[0087] Figure 4 (b) is the vibration deformation test result of BT-G. It can be seen that the sample undergoes bending deformation similar to KNSN-Sn under an AC electric field of 1Hz±750V. The amplitude of the displacement difference can reach 2μm, and the equivalent strain can reach 0.4%.

[0088] 3. Fatigue test, variable temperature test and variable frequency test

[0089] Taking the single-component concentration gradient ceramic prepared in Example 2 as an example, the electrostrain test under variable temperature (from room temperature to 200°C), the variable frequency test (0.1 Hz to 10 Hz) under 20 kV / cm bipolar and unipolar triangular wave excitation, and the 10-cycle test under 20 kV / cm unipolar triangular wave excitation were performed. 6 The fatigue test was repeated several times. The variable temperature test was conducted at 25, 50, 75, 100, 125, 150, 175, and 200°C, taking care to avoid temperature overshoot. The variable frequency test was conducted at 0.1Hz, 1Hz, and 10Hz.

[0090] Figure 5 This is the SE curve fatigue test result of KNSN-Sn piezoelectric ceramics at room temperature. 5 After 10 cycles, the maximum equivalent strain at 20 kV / cm unipolar excitation voltage is about 0.415%; 6 After the first cycle, the maximum strain at a unipolar excitation voltage of 20 kV / cm is about 0.405%, and the maximum strain decays to 93.1% of the initial fatigue state.

[0091] Figure 6 The results of unipolar strain tests on KNSN-Sn piezoelectric ceramics at variable temperatures between 25°C and 200°C are shown. During the temperature test, the electrostrain performance of KNSN-Sn gradually increases with increasing temperature and then decreases, reaching a maximum value at 150°C. At a unipolar excitation voltage of 20 kV / cm, the maximum strain is approximately 0.6%.

[0092] Figure 7 (a) and Figure 7 (b) Variable frequency bipolar strain and unipolar strain test results for KNSN-Sn piezoelectric ceramics at room temperature. In the variable frequency test, the equivalent electrostrain performance of KNSN-Sn increases with decreasing frequency, reaching a maximum at 0.1 Hz. The maximum equivalent strain is approximately 0.9% under bipolar excitation voltage of 20 kV / cm and approximately 0.43% under unipolar excitation.

[0093] 4. Dual-crystal brake performance test

[0094] Preparation of a bimorph actuator: The piezoelectric ceramic prepared in Example 2 was processed using a diamond wire saw into two 28 × 16 × 0.25 mm ceramic sheets. Both surfaces were silver-coated along the thickness direction and then high-temperature polarized at 120°C in an electric field of 30 kV / cm to produce two single crystal sheets. The resulting single crystal sheets were bonded to a 32 × 16 × 0.2 mm nickel plate using epoxy-type conductive silver adhesive along the polarization direction, with electrodes extending therefrom. Drive testing was performed by applying AC electric fields in opposite directions to the two ceramic sheets.

[0095] Figure 8 This is the displacement output of the dual crystals assembled with KNSN-Sn ceramics under ±300V AC excitation. It can be seen that the dual crystals assembled with KNSN-Sn piezoelectric ceramics can achieve a displacement output of ±750μm at a resonant frequency of 50Hz.

[0096] In summary, the large field-induced deformation lead-free piezoelectric ceramic material induced by the defect dipole concentration gradient in the present invention has excellent electro-displacement performance, and not only has a large equivalent electro-strain, but also has a low driving electric field, good fatigue resistance, and a wide operating temperature range. It can be used to process single-layer ceramic drivers, and can also be applied to piezoelectric ceramic elements (such as multi-layer co-fired ceramics), piezoelectric ceramic devices, piezoelectric drivers (such as multi-layer co-fired ceramic drivers, piezoelectric precision drivers), piezoelectric sensors, piezoelectric motors, piezoelectric vibration devices or piezoelectric ejection devices and other fields.

[0097] The above is a preferred embodiment of the present invention, but the present invention should not be limited to the contents disclosed in this embodiment. Therefore, any equivalent or modified implementations that do not depart from the spirit disclosed in the present invention fall within the scope of protection of the present invention.

Claims

1. A lead-free piezoelectric ceramic material with large field-induced deformation induced by defect dipole concentration gradient, characterized in that: Including single-component composition gradient lead-free piezoelectric ceramics and / or multi-component composition gradient lead-free piezoelectric ceramics; The general formula of the single component gradient lead-free piezoelectric ceramic is (Na y K z Sr 1-y-z )Nb 1-x M x O3, M is selected from Nb, Zr, Sn or Sb, x is in the range of 0 to 0.03, y is in the range of 0.45 to 0.55, and z is in the range of 0.45 to 0.55; The multi-component gradient lead-free piezoelectric ceramic is composed of multiple layers of lead-free piezoelectric ceramics with different components, and its general formula is Ba m TiO3, the value range of m is 0.98~1.

2. The lead-free piezoelectric ceramic material with large field-induced deformation induced by defect dipole concentration gradient according to claim 1, characterized in that: M is Sn or Sb, and the value of x ranges from 0.01 to 0.02; The value range of and / or m is 0.99~1.

3. The lead-free piezoelectric ceramic material with large field-induced deformation induced by defect dipole concentration gradient according to claim 1, characterized in that: The chemical formula of the single component gradient lead-free piezoelectric ceramic is (Na 0.49 K 0.49 Sr 0.02 )Nb 0.99 M 0.01 O3, M is selected from Nb, Zr, Sn or Sb; And / or the multi-component composition gradient lead-free piezoelectric ceramic is composed of Ba 0.99 It is composed of TiO3 and BaTiO3.

4. The lead-free piezoelectric ceramic material with large field-induced deformation induced by defect dipole concentration gradient according to claim 1, characterized in that: The crystal structure of the large field-induced deformation lead-free piezoelectric ceramic material is a perovskite structure.

5. The lead-free piezoelectric ceramic material with large field-induced deformation induced by defect dipole concentration gradient according to claim 1, characterized in that: The single-component composition gradient lead-free piezoelectric ceramic obtains a composition gradient by controlling the volatilization of alkali metals during the sintering process. The preparation method includes the following steps: 1) According to the general formula (Na y K z Sr 1-y-z )Nb 1-x M x O3 selects multiple types of potassium carbonate, sodium carbonate, strontium carbonate, niobium pentoxide, zirconium dioxide, tin dioxide and antimony pentoxide as raw materials for batching; 2) adding anhydrous ethanol as a ball milling medium for ball milling, and drying after ball milling to obtain a mixed dry powder; 3) pre-sintering the mixed dry powder at 800-900° C. to form a powder, and adding 2 wt % to 8 wt % of a polyvinyl alcohol aqueous solution to the powder for granulation to obtain a powder; 4) Pressing the powder into a green body, debinding at 550°C, and then sintering at 1150-1200°C to obtain a ceramic sheet; 5) The ceramic wafer is polished, coated with silver electrodes, and then polarized in silicone oil.

6. The lead-free piezoelectric ceramic material with large field-induced deformation induced by defect dipole concentration gradient according to claim 5, characterized in that: In step 3), the mass ratio of the polyvinyl alcohol aqueous solution to the powder is 0.05 to 0.1:1; And / or in step 4), the pressure for pressing the green body is 180-220 MPa, the binder removal treatment time is 3-5 hours, the sintering treatment time is not less than 6 hours, and the crucible cover for sintering is a zirconia ceramic plate with a porosity of 20%; And / or in step 5), the polarization temperature is 100-150° C., the polarization electric field strength is 3-5 kV / mm, and the polarization time is 5-30 min.

7. The lead-free piezoelectric ceramic material with large field-induced deformation induced by defect dipole concentration gradient according to claim 1, characterized in that: The preparation method of the multi-component composition gradient lead-free piezoelectric ceramic comprises the following steps: a) According to the general formula Ba m TiO3 uses barium carbonate and titanium dioxide as raw materials for batching; b) adding anhydrous ethanol as a ball milling medium for ball milling, and drying after ball milling to obtain a mixed dry powder; c) pre-calcining the mixed dry powder at 800-900°C to form a powder, and sieving it through a sieve to obtain a fine powder; d) adding a binder, a dispersant, a defoaming agent and an organic solvent to the fine powder, stirring and mixing to form a slurry, vacuum defoaming the slurry and then performing tape casting to obtain a film tape; e) laminating the membrane strips made of different components into a green body according to a concentration gradient, performing a binder removal treatment at 600° C., and then sintering at 1350° C. to obtain a ceramic sheet; f) The ceramic wafer is polished, coated with silver electrodes, and then polarized in silicone oil.

8. The lead-free piezoelectric ceramic material with large field-induced deformation induced by defect dipole concentration gradient according to claim 7, characterized in that: In step c), the sieve is a 40-mesh sieve; and / or in step d), the binder is a mixture of polyvinyl butyral 30 and 60, the dispersant is dioctyl phthalate, the defoaming agent is n-butanol, and the organic solvent is a mixture of anhydrous ethanol and n-butyl acetate; And / or in step e), the lamination pressure is 180-220 MPa, the lamination temperature is 55-60°C, and the debinding treatment time is 20 hours of heating followed by 10 hours of heat preservation; And / or in step f), the polarization temperature is 120-140° C., the polarization electric field strength is 2-4 kV / mm, and the polarization time is 5-30 min.

9. Application of the large field-induced deformation lead-free piezoelectric ceramic material induced by the defect dipole concentration gradient according to any one of claims 1 to 8 in a piezoelectric element, wherein the piezoelectric element includes a single-layer ceramic piezoelectric driver, a multi-layer ceramic piezoelectric driver, a piezoelectric sensor, a piezoelectric motor, a piezoelectric vibration device or a piezoelectric ejection device.

10. A bimorph piezoelectric element, comprising: upper piezoelectric layer; a conductive metal intermediate layer; lower piezoelectric layer; Wherein, at least one of the piezoelectric layers comprises the large field-induced deformation lead-free piezoelectric ceramic material induced by the defect dipole concentration gradient according to any one of claims 1 to 8.

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