Rubidium lithium titanium germanate piezoelectric crystal, its cut and application

Abstract

This invention provides an application of lithium rubidium titanate crystal as a piezoelectric crystal, wherein the chemical formula of the lithium rubidium titanate crystal is Rb4Li2TiGe4O. 13 The dielectric constant of a piezoelectric crystal is ε. 11 =ε 22 =17.87, ε 33 =52.84, piezoelectric constant is d 31 =d 32 =2.57pC / N, d 33 =10.08pC / N, d 24 =d 15 =3.43pC / N, which is much higher than the piezoelectric effect of SiO2 crystal, making it a piezoelectric material with great application value.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric crystal technology application, and relates to a titanium germanate rubidium lithium piezoelectric crystal, its cutting shape and application. Background Technology

[0002] When certain crystalline materials are deformed by an external force along a certain direction, polarization occurs inside them, causing relative displacement of charged particles and generating equal and opposite charges on opposite surfaces of the crystal. When the external force is removed, the crystal returns to its uncharged state. This phenomenon is called the piezoelectric effect, and the amount of charge generated by the crystal under force is proportional to the magnitude of the external force. Conversely, if an electric field is applied to the crystalline material, the crystal will undergo mechanical deformation in the polarization direction. When the applied electric field is removed, the deformation also disappears. This phenomenon is called the inverse piezoelectric effect, also known as the electrostriction effect. Crystalline materials exhibiting both the piezoelectric and inverse piezoelectric effects are called piezoelectric crystals.

[0003] Piezoelectric crystals are widely used in ultrasonic transducers, surface acoustic wave devices, piezoelectric oscillators, piezoelectric filters, sensors, and other fields. Currently, commercially available piezoelectric crystals mainly include single-crystal quartz (…). α Lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and relaxor ferroelectric PMT-PT, etc.

[0004] Single-crystal quartz possesses advantages such as a zero-frequency coefficient cut and excellent temperature stability, but it has low piezoelectric coefficient and electromechanical coupling factor. Furthermore, under pressure conditions above 350°C, single-crystal quartz tends to form a twinned domain structure, and at 573°C, it undergoes [further changes / reactions]. α -SiO2 direction β -SiO2 phase transition.

[0005] Lithium niobate and lithium tantalate crystals are two very important piezoelectric crystals. Both have large piezoelectric coefficients and electromechanical coupling coefficients, and good high-frequency performance, making them commonly used to fabricate high-frequency broadband filters and high-frequency ultrasonic transducers. However, the temperature coefficient of frequency is negative for all cuts of lithium niobate crystals, and the frequency stability of lithium tantalate crystals is poor at room temperature. Furthermore, both lithium niobate and lithium tantalate crystals require polarization before use.

[0006] Although PMN-PT crystals have very large piezoelectric coefficients and electromechanical coupling coefficients, they contain environmentally unfriendly elements, lack an elastic coefficient and have a zero temperature coefficient, and it is currently difficult to grow PMN-PT single crystals with uniform quality.

[0007] Due to the development of the electronics and communications industries and the need for high-frequency and high-speed communication, people have become interested in new piezoelectric materials capable of fabricating wideband filters and high-frequency stable oscillators. The existing piezoelectric crystals cannot meet these demands, and several new piezoelectric materials, such as lithium tetraborate (Li₂B₄O₇) and LGS (lanthanum gallium silicate) series crystals, have been developed and widely used. Lithium tetraborate has a low temperature delay coefficient, temperature stability comparable to single-crystal quartz, an electromechanical coupling coefficient seven times that of quartz, and a high surface acoustic wave velocity, making it an ideal material for fabricating narrowband surface acoustic wave filters, oscillators, and high-frequency bulk wave devices. However, lithium tetraborate is easily soluble in acids and has slight deliquescence, therefore, certain protective measures are required during device fabrication. LGS series crystals possess almost all the advantages of single-crystal quartz, and their stability, piezoelectric coefficient, and electromechanical coupling coefficient are much higher than those of single-crystal quartz. However, growing large-volume, high-quality LGS series crystals remains difficult. Furthermore, the high melting point and high Ga content of LGS series crystals result in high growth costs.

[0008] As can be seen from the above analysis, although there are many types of piezoelectric crystals, few can be used in practice. Due to their inherent shortcomings, and with the development of modern science and technology, higher requirements have been placed on piezoelectric materials used in aerospace, geological exploration and other fields. Piezoelectric crystal materials are required to have good piezoelectric properties and a wider temperature range, making the development of new piezoelectric crystal materials an urgent task.

[0009] Rb4Li2TiGe4O 13 Lithium rubidium titanate (RLTG) crystal is a novel nonlinear optical crystal. Its crystal structure, transmission spectrum, laser damage threshold, and other fundamental optical properties have been reported (Mingjun Xia, Chuan Tang, Rukang Li, ...). Angew. Chem. Int. Ed. .,2019, 58, 18257–18260. Larger single crystals can be grown using the flux method (Chuan Tang, Mingjun Xia, Rukang Li, J. Cryst. Growth (2021, 555, 125962). However, to date, there have been no reports, either domestically or internationally, on its use in piezoelectric crystals. Summary of the Invention

[0010] To overcome the shortcomings of the prior art, the first objective of this invention is to provide an application of lithium rubidium germanate crystal as a piezoelectric crystal.

[0011] The second objective of this invention is to provide a cut of an RLTG piezoelectric crystal.

[0012] The third objective of this invention is to provide an application of the RLTG piezoelectric crystal.

[0013] The objective of this invention is achieved through the following technical solution.

[0014] An application of lithium rubidium titanate crystal as a piezoelectric crystal, wherein the chemical formula of the lithium rubidium titanate crystal is Rb4Li2TiGe4O 13 .

[0015] According to an embodiment of the present invention, the titanium rubidium lithium germanate crystal belongs to the tetragonal crystal system. P 4nc space group.

[0016] According to an embodiment of the present invention, the titanium germanate rubidium lithium crystal has a 4mm dot group structure.

[0017] The present invention also provides a Rb4Li2TiGe4O 13 For a tetragonal RLTG crystal, the physical axes X, Y, and Z are parallel to the crystallographic axes a, b, and c, respectively. The piezoelectric coefficient of the crystal is... d 33 The positive direction is defined as the +Z-axis, and the negative direction as the -Z-axis, thus determining the Z-axis direction of the RLTG crystal; the X, Y, and Z directions are mutually perpendicular and follow the right-hand rule; the piezoelectric crystal cut is selected from one of the following cuts: Cut type A: A1: X-square cut, refers to a crystal cut where the thickness is cut along the X direction, the length along the Y direction, and the width along the Z direction, with the length and width being the same; A2: Z-square cut, refers to a crystal cut where the thickness is cut along the Z direction, the length along the X direction, and the width along the Y direction, with the length and width being the same; Cut type B: B1: Z-direction crystal rod cut, which refers to a crystal cut where the length is cut along the Z direction, the thickness is cut along the X direction, and the width is cut along the Y direction, and the thickness and width are the same. Cut type C: C1: YZ cut, refers to a crystal cut in which the thickness is along the Y direction and the length is along the Z direction in the physical coordinate axis; C2: ZX cut, refers to a crystal cut in which the thickness is along the Z direction and the length is along the X direction in the physical coordinate axis; Cut type D: D1: ZXt(45°) cut, refers to a crystal cut in which the thickness is along the Z direction and the length is along the X direction in the physical coordinate axis, with the thickness direction as the rotation axis and rotated 45°. D2: YZw(45°) cut, refers to a crystal cut in which the thickness is along the Y direction, the length is along the Z direction, and the width direction is rotated 45° to make a cut in the physical coordinate axis. D3: XZt(45°) cut refers to a crystal cut in which the thickness is along the X direction and the length is along the Z direction in the physical coordinate axis, with the thickness direction as the rotation axis and rotated 45°.

[0018] According to the present invention, cut type B is a crystal cut type with longitudinal stretching vibration mode, cut type C is a crystal cut type with length stretching vibration mode, and cut type D is a crystal cut type with planar shear vibration mode.

[0019] According to an embodiment of the present invention, the crystal cut is a structure having length, width and thickness, such as columnar, square, rectangular, or ring-shaped.

[0020] According to an embodiment of the present invention, in a square slice, length = width > thickness; in a columnar slice, length > width = thickness; and in other slice types, length > width > thickness.

[0021] According to an embodiment of the present invention, the length of the crystal cut is ≥1, preferably the length of the crystal cut is ≥2, for example the length and width are 1, 2 or 4.

[0022] According to an embodiment of the present invention, the length of the crystal cut is less than or equal to 12 mm, preferably less than or equal to 10 mm.

[0023] According to an embodiment of the present invention, the crystal cut A is columnar, with length > width = thickness. For example, the length is 6-12 mm and the width is 6-3 mm. The crystal cut B or C is rectangular, with length > width > thickness. For example, the length is 6-12 mm, the width is 4-2 mm, and the thickness is 1-2 mm.

[0024] According to an embodiment of the present invention, the two corresponding faces of the crystal cut are parallel to each other.

[0025] The present invention also provides an application of the above-mentioned crystal or crystal cut in electronic devices.

[0026] According to an embodiment of the present invention, the electronic device includes an ultrasonic transducer, a surface acoustic wave device, a piezoelectric oscillator, a piezoelectric filter, and a sensor; preferably a narrow-band pass surface acoustic wave filter, an oscillator, or a high-frequency bulk wave device, such as a piezoelectric element.

[0027] A piezoelectric element comprising the aforementioned crystal or a crystal cut.

[0028] A method for fabricating a piezoelectric element includes depositing conductive material on two surfaces of a crystal or crystal cutter to form electrodes, and connecting leads to the electrodes to form a piezoelectric element.

[0029] According to an embodiment of the present invention, the thickness direction of the square or rectangular slice is the direction of the applied electric field, and the height direction of the columnar slice is the direction of the applied electric field.

[0030] As an example, gold or silver electrodes are plated on the two surfaces to which an electric field is applied, and leads are connected to the electrodes; the crystal cut, electrodes and leads together constitute a piezoelectric element.

[0031] piezoelectric constant: Parameters characterizing the coupling relationship between mechanical parameters (stress, strain) and electrical parameters (charge, electric displacement) of piezoelectric materials can be divided into piezoelectric stress constants and piezoelectric strain constants. In this paper, piezoelectric constant is used as an abbreviation for piezoelectric strain constant, involving three independent piezoelectric constants of RLTG crystals; the piezoelectric constant d corresponding to the length-stretching vibration mode. 31 =d 32 The piezoelectric constant d corresponding to the longitudinal stretching vibration mode 33 The piezoelectric constant d corresponding to the surface shear and thickness shear vibration modes 15 =d 24 .

[0032] Explanation of wafer cutting symbols Wafer cut symbols use the notation system specified by the IRE standard, consisting of a set of letters and angles. The first two letters are either X, Y, or Z. The first letter indicates the thickness direction of the wafer before rotation, and the second letter indicates the length direction. For example, YZ cut indicates that the wafer thickness is in the Y direction and the length is in the Z direction. The remaining letters indicate the axis of rotation. The position of the axis of rotation is represented by t (thickness), l (length), and w (width), i.e., t is the axis of rotation in the thickness direction, l is the axis of rotation in the length direction, and w is the axis of rotation in the width direction. If there is only one rotation, the cut symbol has only three letters, and the angle directly indicates the angle of rotation. For example, (YZw)-50° cut indicates that the wafer's original thickness is parallel to the Y-axis, its length is parallel to the Z-axis, and then it is rotated 50 degrees around the width direction. A positive sign for the angle indicates counterclockwise rotation, and a negative sign indicates clockwise rotation.

[0033] AC bridge method By measuring the capacitance and dimensions of the wafer, according to (C represents capacitance, t and A represent the thickness and area of ​​the wafer, respectively.) The method for calculating the dielectric constant (where the dielectric constant is the vacuum dielectric constant).

[0034] Resonance method This method determines the elasticity and piezoelectric constant of the piezoelectric vibrator material by measuring the series frequency (parallel resonant frequency) and other parameters (capacitance, size, density) of the piezoelectric vibrator and performing appropriate calculations.

[0035] The formula used in the above resonance method is as follows:

[0036]

[0037]

[0038]

[0039]

[0040]

[0041] in, s It is the elastic compliance constant. c It is the elastic hardness constant. k The electromechanical coupling coefficient is... d The piezoelectric strain constant is e It is the piezoelectric stress constant; e Where is the dielectric constant. r Crystal density, l For the wafer length, f r and f a These are the resonant frequency and the anti-resonant frequency, respectively.

[0042] Beneficial effects The dielectric constant of the RLTG crystal was obtained by testing using the bridge method and the resonance method. e 11 = e 22 =17.87、 e 33 =52.84, piezoelectric constant is d 31 = d 32 =2.57 pC / N, d 33 =10.08 pC / N, d 24 = d 15 =3.43 pC / N, which is much higher than the piezoelectric effect of SiO2 crystal, making it a piezoelectric material with great application value. Attached Figure Description

[0043] Figure 1 Eight wafer cuts are shown in Embodiment 1 of the present invention. Detailed Implementation

[0044] The following will provide a more detailed description of the wafer, its fabrication method, and its applications based on specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the invention and should not be construed as limiting the scope of protection of the invention. All technologies implemented based on the above description of the invention are covered within the scope of protection intended by the invention.

[0045] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0046] The Rb4Li2TiGe4O used in the embodiments of the present invention 13 The crystals were prepared using a fluxing method.

[0047] Example 1 according to Figure 1 The RLTG crystal is cut according to the specified direction: A 1-X square is obtained, with its thickness along the X direction and dimensions of length × width × height = 4 × 4 × 1.2 mm. 3 ; A 2-Z square is obtained, with its thickness along the Z direction, and its dimensions are: length × width × height = 4 × 4 × 1.2 mm. 3 ; A 3-Z crystal rod was obtained, with its length along the Z-direction and dimensions of: length × width × height = 8 × 4 × 4 mm. 3 ; A 4-YZ wafer was obtained, with its thickness along the Y direction and its length along the Z direction, and its dimensions were: length × width × height = 8 × 4 × 1.6 mm. 3 ; A 5-ZX wafer was obtained, with its thickness along the Z-direction and its length along the X-direction, and its dimensions being: length × width × height = 8 × 4 × 1.6 mm. 3 ; A 6-ZXt(45°) wafer was obtained, with its thickness along the Z direction and its length along the X direction. It was cut by rotating 45° around the thickness direction as the axis of rotation, and its dimensions are: length × width × height = 8 × 4 × 1.6 mm. 3 ; A 7-YZw(45°) wafer was obtained, with its thickness along the Y direction and its length along the Z direction. It was cut by rotating 45° around the width direction as the axis of rotation, and its dimensions are: length × width × height = 8 × 4 × 1.6 mm. 3 ; An 8-XZt (45°) wafer was obtained, with its thickness along the X direction and its length along the Z direction. It was cut by rotating 45° around the thickness direction as the axis of rotation, and its dimensions are: length × width × height = 8 × 4 × 1.6 mm. 3 .

[0048] Test case The following test examples use the AC bridge method and resonance method to measure the packing dielectric constant, piezoelectric constant, elastic constant and electromechanical coupling coefficient of the RLTG crystal obtained in Example 1.

[0049] Selecting piezoelectric coordinate axes, gold electrodes are plated on the two surfaces of a 1-X square plate to apply an electric field, and the relative permittivity is measured using the AC bridge method. .

[0050] Selecting piezoelectric coordinate axes, gold electrodes are plated on both surfaces of a 2-Z square plate to apply an electric field, and the relative permittivity is measured using the AC bridge method. .

[0051] Selecting piezoelectric coordinate axes, gold electrodes are deposited on both surfaces of a 3-Z crystal rod to apply an electric field, and the direct measurement method is used. 33 Static measuring instrument for determining piezoelectric constant d 33 .

[0052] Selecting piezoelectric coordinate axes, gold electrodes are deposited on both surfaces of a 4-YZ wafer to apply an electric field. After electric field polarization, the transverse length stretching vibration mode is used for resonance measurement. d 15 , s 44 .

[0053] Selecting piezoelectric coordinate axes, gold electrodes were plated on both surfaces of the 5-ZX wafer to apply an electric field. After electric field polarization, the transverse length stretching vibration mode was used for resonance measurement. d 31 , s 11 .

[0054] Selecting piezoelectric coordinate axes, gold electrodes were plated on both surfaces of a 6-ZXt (45°) wafer to apply an electric field. After electric field polarization, the elastic constants were measured using the resonance method facing the vibration mode. s 12 .

[0055] Selecting piezoelectric coordinate axes, gold electrodes were plated on both surfaces of the 7-YZw(45°) wafer to apply an electric field. After electric field polarization, the resonance method was used to measure the vibration mode. s 66 .

[0056] Selecting piezoelectric coordinate axes, gold electrodes were plated on both surfaces of an 8-XZt (45°) wafer to apply an electric field. After electric field polarization, the resonance method was used to measure the vibration mode. s 13 .

[0057] according to , d 15 , s44 The calculation results yielded the electromechanical coupling coefficient. k 15 .

[0058] Table 1. Elastic constants, dielectric constants, piezoelectric constants, and electromechanical coupling coefficients of RLTG crystals at room temperature.

[0059]

[0060] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An application of a titanium germanate rubidium lithium crystal as a piezoelectric crystal, wherein, The chemical formula of the lithium titanium germanate crystal is Rb4Li2TiGe4O 13 ; The titanium rubidium lithium germanate crystal belongs to the tetragonal crystal system. P 4nc space group; The titanium germanate rubidium lithium crystal has a 4mm dot group structure. Rb4Li2TiGe4O 13 The cut of a piezoelectric crystal, wherein, for a tetragonal RLTG crystal, the crystal's physical axes X, Y, and Z are parallel to the crystallographic axes a, b, and c, respectively, and the X, Y, and Z axes are mutually perpendicular and follow the right-hand rule: crystal piezoelectricity d 33 The positive direction is defined as the +Z-axis, and the negative direction as the -Z-axis. This determines the Z-axis direction of the RLTG crystal. The cut type is selected from any of the following: Cut type A: A1: X-square cut, refers to a crystal cut where the thickness is cut along the X direction, the length along the Y direction, and the width along the Z direction, with the length and width being the same; A2: Z-square cut, refers to a crystal cut where the thickness is cut along the Z direction, the length along the X direction, and the width along the Y direction, with the length and width being the same; Cut type B: B1: Z-direction crystal rod cut, which refers to a crystal cut where the length is cut along the Z direction, the thickness is cut along the X direction, and the width is cut along the Y direction, and the thickness and width are the same. Cut type C: C1: YZ cut, refers to a crystal cut in which the thickness is along the Y direction and the length is along the Z direction in the physical coordinate axis; C2: ZX cut, refers to a crystal cut in which the thickness is along the Z direction and the length is along the X direction in the physical coordinate axis; Cut type D: D1: ZXt(45°) cut, refers to a crystal cut in which the thickness is along the Z direction and the length is along the X direction in the physical coordinate axis, with the thickness direction as the rotation axis and rotated 45°. D2: YZw(45°) cut, refers to a crystal cut in which the thickness is along the Y direction, the length is along the Z direction, and the width direction is rotated 45° to make a cut in the physical coordinate axis. D3: XZt(45°) cut, refers to a crystal cut in which the thickness is along the X direction and the length is along the Z direction in the physical coordinate axis, with the thickness direction as the rotation axis and rotated 45°. Type B is a crystal cut for the longitudinal stretching vibration mode, type C is a crystal cut for the length stretching vibration mode, and type D is a crystal cut for the planar shear vibration mode.

2. The application according to claim 1, wherein: When the crystal cut A is columnar, the length of the column is 6-12 mm and the width is 6-3 mm; When the crystal cut B or C is rectangular, the length of the rectangular sheet is 6-12 mm, the width is 4-2 mm, and the thickness is 1-2 mm.

3. The application according to claim 1, wherein: The two corresponding faces of the piezoelectric crystal are parallel to each other.

4. A method for fabricating a piezoelectric element, comprising Rb4Li2TiGe4O as described in any one of claims 1-3. 13 A piezoelectric crystal is cut into a shape on which an electric field is applied. The two surfaces are coated with conductive material to form electrodes. The electrodes are connected to external leads to form a piezoelectric device.

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