High-temperature piezoelectric functional crystal calcium borate lanthanum thulium oxide crystal material as well as growth method and application thereof

Abstract

The invention relates to a high-temperature piezoelectric functional crystal calcium borate lanthanum thulium oxide crystal material as well as a growth method and application thereof, and belongs to the field of crystal growth technologies and application. The chemical formula is # imgabs0 #, and x ranges from 0.08 to 0.25. By introducing Tm, the mobility of hole carriers in the LaCOB crystal is remarkably reduced, so that the order of magnitude of resistivity is improved. By doping Tm ions to La and Ca sites, the dielectric response of the LaCOB crystal is significantly enhanced. The significant Jahn-Teller distortion caused by Tm ions breaks the spatial symmetry of the octahedron, and induces the aggravation of low-frequency phonon vibration, thereby effectively enhancing the lattice polarization response. Through growth atmosphere regulation and control and Czochralski growth, the Tm-doped LaCOB crystal is remarkably improved in the aspects of resistance and dielectric properties.

Description

Technical Field

[0001] The present invention relates to a high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material and a growth method and application thereof, belonging to the field of crystal growth technology and application. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Rare earth calcium borate crystals (RECa4O(BO3)3, RECOB, RE: rare earth element) not only have excellent stability under high temperature conditions, but also have high melting point (1400-1520℃) and ultra-high resistivity (>10 6 Ω·cm@900℃), and the advantage of growing large single crystals, show promising applications in high-temperature piezoelectrics. Although the dielectric activity of RECOB crystals is relatively low, which may affect the stability of signal sensitivity and energy conversion efficiency, the dielectric response is closely related to the RE ion radius, providing a potential regulatory pathway for optimizing their piezoelectric properties.

[0004] The resistive properties and dielectric parameters of RECOB crystals are crucial for their practical applications. Resistivity suppresses leakage current and temperature drift of performance parameters, while dielectric response influences the stability of signal sensitivity and energy conversion efficiency. It has been reported that the resistive and dielectric properties of RECOB crystals are significantly dependent on the type and occupancy of the RE ions. The resistivity of RECOB crystals decreases with increasing RE ion radius, with ErCOB and YCOB, with smaller ionic radii, exhibiting the highest resistivity, approximately one to two orders of magnitude higher than GdCOB, NdCOB, and LaCOB, with larger ionic radii. The dielectric constant increases with increasing RE ion radius. However, when the RE ion radius is increased to La, the dielectric constant of LaCOB crystals decreases significantly. Single crystal X-ray diffraction studies have revealed the widespread presence of RE / Ca antisite defects in RECOB crystals, which can aggravate ion displacement and significantly affect dielectric polarization. Notably, among the RECOB series, LaCOB exhibits an extremely low concentration of RE / Ca antisite defects, which may be a key factor in its reduced dielectric response. Different from other RECOB crystals, La can occupy both Ca1 and Ca2 sites at the same time.

[0005] LaCOB crystals have very high dielectric stability, starting from room temperature ( = 15.0) to 1000°C ( =15.2), with very little variation. Therefore, it is necessary to carefully control the selection and doping sites of RE elements to optimize the dielectric response and resistance properties, thereby enhancing the application potential of RECOB in the field of high-temperature piezoelectric sensing. Summary of the Invention

[0006] In order to solve the shortcomings of the prior art, the purpose of the present invention is to provide a high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material and its growth method and application. The present invention doped Tm into the cation site of LaCOB crystal to obtain calcium borate lanthanum oxide thulium crystal, and LaCOB ( ) crystals, the high-temperature stability and piezoelectric properties of the material are significantly enhanced.

[0007] In order to achieve the above object, the technical solution of the present invention is: In the first aspect, a high temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material, the chemical formula is , x is 0.08~0.25.

[0008] In a second aspect, a method for growing the above-mentioned high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material comprises the following steps: The calcium source, lanthanum source and thulium source are mixed according to the stoichiometric ratio, and the boron source is mixed according to the stoichiometric ratio by 1-3%, and the mixed raw materials are mixed uniformly to obtain a mixed raw material; sintering the mixed raw materials to prepare calcium borate lanthanum thulium oxide polycrystalline material; Under inert atmosphere, the polycrystalline material is heated and melted to form a uniformly melted calcium borate lanthanum thulium oxide melt; Under inert atmosphere conditions, using LaCOB crystals or crystals of the same structure as LaCOB as seed crystals, a Czochralski method is used to grow crystals from the calcium borate lanthanum thulium oxide melt to obtain calcium borate lanthanum thulium oxide crystals; The calcium borate lanthanum thulium oxide crystal is heated to 1100-1200° C. and annealed to obtain the result.

[0009] Compared with other isomorphous crystals, the consistent melting zone of the calcium borate lanthanum thulium oxide crystal provided by the present invention is very narrow. Therefore, the method of excessive boron source is used to compensate for the component deviation caused by the volatilization of boron during crystal growth, thereby obtaining high-quality single crystals.

[0010] At the same time, high temperature annealing treatment can not only fully release the thermal stress generated during crystal growth, but also enable Tm to be doped into the Ca1 site, thereby significantly improving the dielectric constant ( ε 22), thus having higher high temperature stability and piezoelectric performance than LaCOB crystal.

[0011] In some embodiments, during the Czochralski method of growing crystals, the seed crystals used are b-oriented seed crystals, and the seed crystals are oriented along the The crystal grows along the crystallographic axis b. The crystal grows faster along the crystal axis b and the crystal quality is higher. The b direction is the best growth direction for the crystal.

[0012] In the third aspect, an application of the above-mentioned high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material in high-temperature piezoelectric sensing.

[0013] The high temperature in the high temperature piezoelectric sensor described in the present invention refers to a temperature not lower than 650°C.

[0014] In a fourth aspect, a method for enhancing the high-temperature resistivity and dielectric properties of LaCOB crystals is provided, wherein a thulium source is added during the preparation of the LaCOB crystals, and the thulium is doped into the Ca1 site of the LaCOB crystals.

[0015] Specifically, the method is detailed in the method for growing the high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material described in the second aspect of the present invention.

[0016] The beneficial effects of the present invention are: The calcium borate lanthanum oxide thulium grown by the present invention ( ) A new type of high-temperature piezoelectric crystal has a non-centrosymmetric m-point group crystal configuration, has good mechanical properties, is not easy to deliquesce, melts uniformly, and can be used to grow large-sized high-quality single crystals in a relatively short time using the pulling method. By doping Tm ions into the La and Ca sites, the dielectric response of the LaCOB crystal is significantly enhanced. The doping of Tm significantly improves the Jahn-Teller distortion of the crystal by introducing a smaller ionic radius and a larger mass, breaking the high symmetry of the La-O6 and Ca-O6 octahedra. This structural modification effectively enhances the low-frequency optical branch rotational vibration mode of the La / Tm / Ca-O6 octahedron, increases the static dipole moment, and improves the dielectric response of the crystal. The present invention also further optimizes the doping concentration of Tm at the Ca site by controlling the annealing temperature and the oxygen-poor or boron-rich atmosphere, which can further enhance the dielectric properties.

[0017] The invention grows The crystal resistivity can be improved by an order of magnitude compared to LaCOB. Compared to LaCOB, the introduction of Tm reduces the dispersion of the valence band top, increases the effective mass of holes, and thus suppresses hole migration.

[0018] In summary, the present invention provides a design method for Tm-doped LaCOB crystals, which significantly improves the dielectric response of the crystal by enhancing Jahn-Teller distortion and optimizing the doping concentration; and suppresses the migration of hole carriers by increasing the effective mass of holes in the system. After design, a high resistance and high dielectric response crystal for high-temperature sensors can be obtained. crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0020] Figure 1 This is a diagram of the energy band structure in Example 1 of the present invention.

[0021] Figure 2 3 is a comparison diagram of the resistivity before and after Tm doping in Example 3 and Example 5 of the present invention.

[0022] Figure 3 This is the Jahn-Teller distortion diagram of the octahedral structure before and after Tm doping in Example 1 of the present invention.

[0023] Figure 4 1 is a diagram of the octahedral net dipole moment before and after Tm doping in Example 1 of the present invention.

[0024] Figure 5 This is a diagram of dielectric-dependent phonon frequency contribution of Tm doped at different sites in Example 1 of the present invention.

[0025] Figure 6 For Example 1 and Comparative Example 2 of the present invention Diagram of crystal growth atmosphere control.

[0026] Figure 7 Graph showing the dielectric constants of different sites doped with Tm in Example 1 of the present invention.

[0027] Figure 8 Actual images of the crystals prepared in Examples 3, 4, and 5 of the present invention. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0030] In view of the fact that the high-temperature resistivity and dielectric properties of existing LaCOB crystals need to be further improved, the present invention proposes a high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material and its growth method and application.

[0031] A typical embodiment of the present invention provides a high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material, the chemical formula is , x is 0.08~0.25.

[0032] In some embodiments, Tm is incorporated into the Ca1 site of the LaCOB crystal.

[0033] In some embodiments, Tm is incorporated into the La site of the LaCOB crystal.

[0034] A second embodiment of the present invention provides a method for growing the above-mentioned high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material, comprising the following steps: The calcium source, lanthanum source and thulium source are mixed according to the stoichiometric ratio, and the boron source is mixed according to the stoichiometric ratio by 1-3%, and the mixed raw materials are mixed uniformly to obtain a mixed raw material; sintering the mixed raw materials to prepare calcium borate lanthanum thulium oxide polycrystalline material; Under inert atmosphere, the polycrystalline material is heated and melted to form a uniformly melted calcium borate lanthanum thulium oxide melt; Under inert atmosphere conditions, using LaCOB crystals or crystals of the same structure as LaCOB as seed crystals, a Czochralski method is used to grow crystals from the calcium borate lanthanum thulium oxide melt to obtain calcium borate lanthanum thulium oxide crystals; The calcium borate lanthanum thulium oxide crystal is heated to 1100-1200° C. and annealed to obtain the result.

[0035] The calcium source of the present invention refers to a salt or base whose cation is calcium ion, or a calcium oxide, such as calcium oxide, calcium carbonate, calcium bicarbonate, calcium hydroxide, calcium acetate, calcium oxalate, etc. Calcium carbonate or calcium oxide is generally used as a calcium source for preparing crystals.

[0036] The lanthanum source of the present invention is lanthanum oxide or a salt or base in which the cation is a lanthanum ion, for example 、 , lanthanum acetate, etc. Generally used or As a lanthanum source for preparing crystals.

[0037] The thulium source of the present invention is a thulium oxide or a salt or base whose cation is a thulium ion, for example 、 , thulium acetate, etc. Generally used or As a thulium source for preparing crystals.

[0038] The boron source of the present invention is generally boron oxide ( ) or boric acid.

[0039] In some embodiments, the sintering process is performed at least twice to prepare the calcium borate lanthanum thulium oxide polycrystalline material. The growth quality of the crystal can be ensured by sintering multiple times.

[0040] In a specific embodiment, the sintering process is as follows: the mixed raw materials are heated to 900-950°C for primary sintering; the sintered materials after the primary sintering are crushed and refined and mixed evenly, and then pressed into shape and heated to 1100-1150°C for secondary sintering. Specifically, the primary sintering is used to decompose and remove and The primary sintering time is 10 to 20 hours. Specifically, the secondary sintering is a solid phase reaction stage for sintering to form a calcium borate lanthanum thulium oxide polycrystalline material; the secondary sintering time is 20 to 30 hours.

[0041] In some embodiments, the polycrystalline material is heated and melted by first subjecting the polycrystalline material to at least two melting and congealing cycles; then, the congealed material obtained from the final melting and congealing cycle is heated until melted, and the melt is superheated by 20-50°C and maintained at a constant temperature to obtain a uniformly melted lanthanum thulium calcium oxyborate melt. Multiple melting and congealing cycles (melting at elevated temperatures followed by congealing at lower temperatures) can effectively expel bubbles generated in the melt, thereby reducing crystal growth defects (such as bubbles and inclusions) and improving crystal growth quality. Specifically, the melting and congealing cycles are repeated three to four times. Specifically, the constant temperature period is 10-20 hours.

[0042] In some embodiments, the polycrystalline material is heated and melted in an iridium crucible. Specifically, when the iridium crucible is used for heating and melting, it is evacuated and filled with a protective gas of nitrogen or an inert gas to prevent oxidation of the iridium at high temperature.

[0043] In some embodiments, during the Czochralski method of growing crystals, the seed crystals used are b-oriented seed crystals, and the seed crystals are The crystal grows along the crystallographic axis b. Specifically, a b-direction seed crystal is vertically lowered into a calcium borate lanthanum thulium oxide melt until the top of the seed crystal is perpendicular to and just in contact with the melt, and single crystal growth begins along the b direction.

[0044] In some embodiments, the temperature for single crystal growth is 1400-1420°C.

[0045] In some embodiments, the crystal growth goes through four stages: necking, shouldering, equal diameter growth, and crystal lifting.

[0046] LaCOB crystals are prone to cracking on the (-201) plane during growth. To reduce cracking and obtain high-quality single crystals, after extracting the crystal, the temperature is first raised to 30-50°C, the crystal is kept constant in a temperature field for 1-2 hours, and then cooled to room temperature at a rate of 5-20°C / hour. The fastest cooling rate should not exceed 20°C / hour.

[0047] Specifically, during the crystal growth process, the pulling speed is 0.5-3 mm / hour and the rotation speed is 4-8 rpm when the seed crystal is necked; the pulling speed is reduced to 0.3-1 mm / hour and the rotation speed is 6-8 rpm when the shoulder is released; the pulling speed is 0.3-0.8 mm / hour and the rotation speed is 6-8 rpm for equal-diameter growth; when the crystal grows to the required size, the crystal is ready to be removed; the removal process is as follows: slowly increase the temperature at a rate of 20-50°C / hour, and when the temperature is increased and it is observed that the bottom of the crystal has a tendency to shrink inward, the pulling speed is increased to 10-15 mm / hour to pull the crystal out of the melt.

[0048] More specifically, a secondary necking method is adopted in the necking process. When the seed crystal is lowered for the first time, the pulling speed is controlled to 0.5~3 mm / hour and the rotation speed is 4~8 rpm. When the diameter of the seed crystal is reduced to 0.5~2.0 mm, the temperature is slowly lowered at 0.5~5 ℃ / hour to release the shoulder. During the shoulder release process, the pulling speed is reduced to 0.3~1 mm / hour and the rotation speed is 6~8 rpm. When the shoulder size of the crystal reaches 3~5 mm, secondary necking is performed. When the diameter of the seed crystal is reduced to 0.5~2.0 mm, secondary shoulder release is performed. When the diameter of the crystal shoulder reaches the predetermined size of 20~40 mm, the temperature is increased or decreased at a rate of 0~5 ℃ / hour (not 0 ℃ / hour) to perform equal diameter growth. The pulling speed is 0.3~0.8 mm / hour and the rotation speed is 6~8 rpm. When the crystal is pulled to a height of 20~50 mm, the crystal is ready to be removed. The specific operation of the removal process is as follows: with 20~50 The temperature was slowly increased at a rate of ℃ / hour, and the pulling speed was increased to 5-10 mm / hour. When the temperature was increased and it was observed that the bottom of the crystal had a tendency to shrink inward, manual pulling was switched to pull the crystal out of the melt.

[0049] When using an iridium crucible, the growth is carried out under a nitrogen or inert gas atmosphere to prevent oxidation of the iridium at high temperatures. The volume fraction of nitrogen or inert gas is 95-98%.

[0050] In some embodiments, the annealing time is 48 to 60 hours.

[0051] In order to increase the occupancy of Tm at La and Ca1 sites, in some embodiments, the annealing temperature is 1190-1200°C.

[0052] A third embodiment of the present invention provides an application of the above-mentioned high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material in high-temperature piezoelectric sensing.

[0053] A fourth embodiment of the present invention provides a method for enhancing the high-temperature resistivity and dielectric properties of LaCOB crystals, wherein a thulium source is added during the preparation of the LaCOB crystals, and the thulium is doped into the Ca1 site of the LaCOB crystals.

[0054] Specifically, the method of doping thulium into the Ca1 site of the LaCOB crystal is detailed in the method for growing the high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material described in the second embodiment of the present invention.

[0055] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0056] The purity of the raw materials in the examples and comparative examples is greater than 99.99%.

[0057] Example 1 (1) 、 、 、 As raw materials, according to the chemical formula of calcium borate lanthanum thulium oxide (x=0.08), using stoichiometric ratio, 2% overdose.

[0058] (2) The raw materials prepared in step (1) were fully mixed and placed in a ceramic crucible for the first sintering at a temperature of 930°C for 20 hours to decompose and remove and .

[0059] The temperature was lowered, the primary sintered material was ground finely, mixed evenly again, pressed into blocks, and placed in a ceramic crucible for solid phase reaction. The sintering temperature was 1150° C. and kept constant for 20 hours to obtain the calcium borate lanthanum thulium oxide polycrystalline raw material.

[0060] (3) The calcium borate lanthanum oxide thulium polycrystalline material obtained in step (2) is placed in an iridium crucible in a single crystal furnace. The furnace is evacuated and filled with nitrogen as a protective gas. The polycrystalline raw material is heated to melt using medium frequency induction heating. After the polycrystalline material is completely melted, the temperature is lowered to solidify, and then the temperature is raised again to melt it completely. This is repeated 4 times to remove bubbles generated in the melt. The melt is then superheated to 20°C and kept at a constant temperature for 10 hours to obtain a uniformly melted calcium borate lanthanum oxide thulium melt. (4) Slowly immerse the b-direction seed crystal taken from the LaCOB crystal into the polycrystalline melt of step (3) until the top of the seed crystal is perpendicular to and just in contact with the melt, and start single crystal growth along the b direction; when the seed crystal necks, the pulling speed is 0.5 mm / hour and the rotation speed is 8 rpm; when the shoulder is released, the pulling speed is reduced to 0.3 mm / hour and the rotation speed is 6 rpm; the pulling speed for equal diameter growth is 0.5 mm / hour and the rotation speed is 8 rpm. When the crystal grows to the desired size of 40 mm in height, the crystal is ready to be removed; the removal process is as follows: slowly increase the temperature at a rate of 20°C / hour. When the bottom of the crystal is observed to have a tendency to shrink inward during the temperature increase, manually pull the crystal to separate it from the melt. Step (4) is carried out under the condition of nitrogen as the protective gas.

[0061] (5) After the calcium borate lanthanum thulium oxide crystals were extracted, the temperature was raised to 30 °C, the crystals were kept constant in the temperature field for 2 hours, and then cooled to room temperature at a rate of 20 °C / hour to obtain calcium borate lanthanum thulium oxide crystals.

[0062] (6) After taking out the calcium borate lanthanum oxide thulium crystal, it needs to be placed in a high-temperature resistance furnace for annealing in air at a temperature of 1200 °C for 48 hours.

[0063] Example 2 (1) Different from Example 1, 、 、 、 As raw materials, according to the chemical formula of calcium borate lanthanum thulium oxide (x=0.15), using stoichiometric ratio, adding 2% overdose.

[0064] (2) The crystal growth process and crystal annealing treatment are the same as in Example 1.

[0065] Example 3 (1) The difference from Example 1 is that 、 、 、 As raw materials, according to the chemical formula of calcium borate lanthanum thulium oxide (x=0.15), using stoichiometric ratio ingredients, using stoichiometric ratio ingredients, adding 2% overdose.

[0066] (2) The crystal growth process is the same as in Example 1.

[0067] (3) Different from Example 1, the crystal is annealed in nitrogen at a temperature of 1200°C.

[0068] The crystal material prepared in this example is denoted as Tm: LaCOB 1.

[0069] Example 4 This embodiment is the same as embodiment 1, except that: (1) Different from Example 1, 、 、 、 As raw materials, according to the chemical formula of calcium borate lanthanum thulium oxide (x=0.25), using stoichiometric ratio ingredients, using stoichiometric ratio ingredients, adding 3% overdose.

[0070] (2) The crystal growth and annealing process are the same as in Example 1.

[0071] Example 5 This embodiment is the same as embodiment 1, except that: (1) Different from Example 1, 、 、 、 As raw materials, according to the chemical formula of calcium borate lanthanum thulium oxide (x=0.25), using stoichiometric ratio ingredients, using stoichiometric ratio ingredients, adding 3% overdose.

[0072] (2) Different from Example 1, a secondary necking is performed during the crystal growth process in Example 5. The other growth processes are the same as in Example 1.

[0073] (3) The crystal growth process and annealing treatment are the same as in Example 1.

[0074] The crystal material prepared in this example is denoted as Tm: LaCOB 2.

[0075] Comparative Example 1 This comparative example is the same as Example 1, except that: (1) Different from Example 1, 、 、 As raw materials, according to the chemical formula of calcium borate lanthanum oxide , using stoichiometric ratio ingredients, using stoichiometric ratio ingredients, adding 3% overdose.

[0076] (2) The crystal growth process and annealing treatment are the same as in Example 1.

[0077] The crystal material prepared in this embodiment is denoted as LaCOB.

[0078] Comparative Example 2 This comparative example is the same as Example 1, except that: (1) Platinum crucibles were used in both the melting process and the crystal growth process, and the atmosphere used was air.

[0079] Experimental example The dielectric constant (ε) of the crystals used in the examples and comparative examples was measured using the parallel plate capacitance method with an LCR meter (Agilent 4294A) in the frequency range of 1 kHz to 1 MHz. Platinum thin film electrodes with a thickness of 200 ± 10 nm and an effective electrode area of 5.0 × 5.0 mm² were sputtered onto the parallel large surfaces of the crystals (perpendicular to the thickness direction) using an ion sputtering instrument (ETD-3000). Resistance measurements were performed using a source measurement unit (Keithley 2410C) coupled with a high-temperature probe station.

[0080] Figure 1 This indicates that the introduction of Tm changes the dispersion of the band structure. In particular, the band curvature of the Tm:LaCOB system becomes flatter near the VBM and CBM regions, which means that the migration of hole and electron carriers will be suppressed, and the resistance properties are expected to be improved.

[0081] Figure 2 The results show that the temperature-dependent resistivity of LaCOB crystals before and after Tm doping is different. Within the temperature range of 500°C to nearly 900°C, the resistivity increases significantly by approximately one to two orders of magnitude. This improved resistivity contributes to the stability of piezoelectric signal sensing.

[0082] The effect of the introduction of Tm on the local octahedral structure in the crystal, such as Figure 3 The formula required to calculate the Jahn-Teller distortion is as follows: (1) where (O1, O4), (O2, O5), and (O3, O6) represent the relative oxygen atoms in the octahedral structure. Increased Jahn-Teller distortion implies a decrease in the degeneracy of the octahedral structure and may induce relative displacements between anions and cations, thereby enhancing the ionic polarization contribution. Figure 3 It shows that Tm doping can significantly increase the degree of Jahn-Teller distortion, especially significantly reducing the symmetry of the La-O6 octahedral structure.

[0083] The effect of the introduction of Tm on the dipole moment of the octahedral structure in the crystal, such as Figure 4 Compared with the very low net dipole moment in the pure phase, Tm doping can significantly increase the dipole polarizability of the crystal.

[0084] Figure 5 The contribution of phonon-induced polarization response in different systems is shown. The calculation is obtained according to the following formula: (2) in, V is the volume, =1 amu, is the dielectric constant of free space, It is along α Direction λ Mode-effective charge of th phonon.

[0085] (3) It's an atom i The Born effective charge tensor of , is the atomic mass, It is along γ Direction of atoms i Model λ The normalized component of the phonon vibration vector.

[0086] like Figure 5 As shown, the introduction of Tm significantly reduces the phonon response to dielectric polarization, changing it from highly symmetric stretching or rotational vibration to low-frequency asymmetric rotational vibration.

[0087] Figure 6 The effect of atmosphere control on the doping defect sites and concentration is demonstrated. When the crystal growth atmosphere is adjusted from an oxygen-rich environment to an oxygen-poor atmosphere, Tm Ca The doping concentration can be further significantly increased.

[0088] Figure 7 The effect of Tm doping on the dielectric constant of LaCOB crystal is shown. Ca 0 YY doping can significantly improve the dielectric constant of LaCOB crystal.

[0089] contrast Figure 2 、 6 and Figure 7 It can be seen that after the present invention doped LaCOB crystal with Tm, the resistivity was increased by an order of magnitude, and the dielectric response was significantly improved. In particular, after high-temperature annealing treatment, the concentration of Tm-doped Ca sites was increased, and the dielectric constant was further improved.

[0090] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material, characterized in that: The chemical formula is , x is 0.08~0.

25.

2. The high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material according to claim 1, characterized in that: Tm is incorporated into the Ca1 site of LaCOB crystals; Alternatively, Tm is incorporated into the La site of the LaCOB crystal.

3. A method for growing the high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material according to claim 1 or 2, characterized in that: The steps include: The calcium source, lanthanum source and thulium source are mixed according to the stoichiometric ratio, and the boron source is mixed according to the stoichiometric ratio by 1-3%, and the mixed raw materials are mixed uniformly to obtain a mixed raw material; sintering the mixed raw materials to prepare calcium borate lanthanum thulium oxide polycrystalline material; Under inert atmosphere, the polycrystalline material is heated and melted to form a uniformly melted calcium borate lanthanum thulium oxide melt; Under inert atmosphere conditions, using LaCOB crystals or crystals of the same structure as LaCOB as seed crystals, a Czochralski method is used to grow crystals from the calcium borate lanthanum thulium oxide melt to obtain calcium borate lanthanum thulium oxide crystals; The calcium borate lanthanum thulium oxide crystal is heated to 1100-1200° C. and annealed to obtain the result.

4. The growth method according to claim 3, wherein: The sintering is performed at least twice to form the calcium borate lanthanum thulium oxide polycrystalline material; Alternatively, the sintering process is as follows: heating the mixed raw materials to 900-950°C for primary sintering; crushing and refining the sintered materials after the primary sintering and mixing them evenly, then pressing and molding them, and heating them to 1100-1150°C for secondary sintering; preferably, the primary sintering time is 10-20 hours; preferably, the secondary sintering time is 20-30 hours.

5. The growth method according to claim 3, wherein: The process of heating and melting the polycrystalline material is as follows: first, subjecting the polycrystalline material to at least two melting and solidification processes; then, heating the solidified material obtained in the last melting and solidification process until it is melted, and superheating the melt by 20 to 50° C. and maintaining the temperature to obtain a uniformly melted calcium borate lanthanum thulium oxide melt.

6. The growth method according to claim 3, wherein: During the crystal growth process of the Czochralski method, the seed crystal used is the b-direction seed crystal, and along The crystal grows along the crystallization axis b direction; preferably, the seed crystal in the b direction is vertically lowered into the calcium borate lanthanum thulium oxide melt until the top of the seed crystal is perpendicular to and just contacts the melt, and the single crystal growth begins along the b direction; Alternatively, the temperature of single crystal growth is 1400~1420℃.

7. The growth method according to claim 3, wherein: The crystal growth goes through four stages: necking, shouldering, equal diameter growth and crystal extraction. Preferably, after the crystal is extracted, the temperature is first raised to 30-50°C, the crystal is kept at a constant temperature for 1-2 hours in a temperature field, and then cooled to room temperature at a rate of 5-20°C / hour. Alternatively, during the crystal growth process, when the seed crystal is necked, the pulling speed is 0.5~3 mm / hour, and the rotation speed is 4~8 rpm; when the shoulder is released, the pulling speed is reduced to 0.3~1 mm / hour, and the rotation speed is 6~8 rpm; when the equal-diameter growth is carried out, the pulling speed is 0.3~0.8 mm / hour, and the rotation speed is 6~8 rpm; when the crystal grows to the required size, the crystal is ready to be removed; the removal process is as follows: slowly increase the temperature at a rate of 20~50℃ / hour. When the temperature is increased and it is observed that the bottom of the crystal has a tendency to shrink inward, the pulling speed is increased to 10~15 mm / hour to pull the crystal out of the melt.

8. The growth method according to claim 3, wherein: Annealing time is 48~60 hours; Alternatively, the annealing temperature is 1190~1200 ℃.

9. Use of the high-temperature piezoelectric functional crystal calcium borate lanthanum oxide thulium crystal material according to claim 1 or 2 in high-temperature piezoelectric sensing.

10. A method for enhancing the high temperature resistivity and dielectric properties of LaCOB crystals, characterized by: During the preparation of LaCOB crystals, a thulium source is added, and thulium is incorporated into the Ca1 site of the LaCOB crystals; Preferably, the method for doping thulium into the Ca1 site of LaCOB crystal is the growth method according to any one of claims 3 to 8.

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