A method for preparing a tetragonal transparent potassium tantalate niobate crystal

Abstract

The present application relates to the technical field of photoelectric functional crystal materials, in particular to a preparation method of tetragonal transparent potassium tantalum niobate crystal, comprising the following steps: (1) plating electrodes on the surface of the crystal; (2) controlling the temperature of the potassium tantalum niobate crystal with plated electrodes to be within the range of 2-6 ℃ below the Curie point and keeping it constant all the time; (3) polarizing the crystal by applying an alternating electric field under ultraviolet laser irradiation to obtain the tetragonal transparent potassium tantalum niobate crystal. The potassium tantalum niobate crystal prepared by the method can maintain a transparent state for a long time without a large thermal shock, solving the problem that the tetragonal potassium tantalum niobate crystal cannot be applied in the field of electro-optical modulation due to low light transmittance, and also solving the problem of light scattering caused by micro-domain walls of the cubic potassium tantalum niobate crystal near the Curie point.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoelectric functional crystal materials, and particularly relates to a preparation method of a tetragonal transparent potassium tantalum niobate crystal. BACKGROUND

[0002] The electro-optic effect is a phenomenon that the refractive index of a crystal changes under the action of an applied voltage. According to the relationship between the change of the refractive index and the voltage, the electro-optic effect can be divided into linear electro-optic effect and quadratic electro-optic effect. Common electro-optic crystals include lithium niobate and potassium dideuterium phosphate, which both utilize the linear electro-optic properties of the crystals and have been widely used in the fields of optical modulation and laser devices.

[0003] Potassium tantalum niobate crystal (KTa 1-x Nb x O3, abbreviated as KTN) is a new type of electro-optic crystal material developed in recent years. The crystal is in a transparent cubic phase above the Curie point, has the largest quadratic electro-optic coefficient of the currently known materials, and can be used for making electro-optic modulation and deflection devices due to its excellent electro-optic properties, and has great application potential in the fields of optical communication, medical imaging and radar scanning. The KTN crystal will undergo a transition from cubic phase to tetragonal phase from high temperature to low temperature. According to Curie-Weiss law, the crystal has the largest electro-optic coefficient near the Curie point, but when the temperature of the crystal decreases to the Curie point, the disordered dipoles in the crystal will first gather into polar micro regions with consistent orientation in the nanoscale range and gradually evolve into polar micro domains. When the temperature continues to decrease to below the Curie point, the crystal changes into tetragonal phase and forms micron-scale ferroelectric domains. Due to the existence of domain walls, the tetragonal KTN crystal presents an opaque state, which will cause light scattering and reflection when laser is incident, thereby reducing the light transmittance. Therefore, although the tetragonal KTN crystal also has excellent linear electro-optic properties, it cannot be applied in the field of electro-optics.

[0004] Two methods have been reported to achieve the transparent state of tetragonal KTN crystal (Li X, Yang Q, Zhang X, et al. High transparency induced by electric fields using KTN crystals [J]. Journal of Alloys and Compounds, 2020, 842: 155702.). The first method is to apply a direct current electric field on the crystal, so that the polarization direction of the ferroelectric domain in the crystal is consistent, and the domain wall disappears, thereby making the crystal transparent. However, this single-domain transparent state can only be maintained for tens of minutes after the voltage is removed. The second method is to apply an alternating current voltage of kHz or higher frequency on the crystal, which will cause the crystal to heat up and change from the opaque tetragonal phase to the transparent cubic phase. However, after the voltage is removed and the temperature decreases, the crystal will return to the tetragonal phase and become opaque again. Therefore, there is a need for a method that can convert the tetragonal KTN crystal into a transparent state and maintain this state for a long time. SUMMARY

[0005] In order to solve the technical problem that the tetragonal potassium tantalum niobate crystal cannot maintain a transparent state for a long time after being converted into a transparent state, the present application provides a method for preparing a tetragonal transparent potassium tantalum niobate crystal. The potassium tantalum niobate crystal prepared by this method can maintain a transparent state for a long time without significant thermal shock.

[0006] The present application provides a method for preparing a tetragonal transparent potassium tantalum niobate crystal, comprising the following steps:

[0007] (1) Plating electrodes on the surface of the crystal;

[0008] (2) Controlling the temperature of the potassium tantalum niobate crystal with plated electrodes to be within the range of 2-6℃ below the Curie point and maintaining it constant;

[0009] (3) Polarizing the crystal by applying an alternating electric field under ultraviolet laser irradiation to obtain a tetragonal transparent potassium tantalum niobate crystal.

[0010] Under the condition of ultraviolet laser irradiation, the method of alternating electric field polarization is used to break the micron-scale ferroelectric domains in the crystal into nanoscale polar microdomains (PNR), achieving crystal transparency. This transparent state can be maintained for a long time without significant thermal shock. The transparent state of the crystal does not change significantly when the temperature is adjusted within the temperature range of -100-100℃.

[0011] Further, in step (1), the chemical formula of the potassium tantalum niobate crystal is KTa 1-x Nb x O3, wherein x is in the range of 0.3-0.5.

[0012] Further, in step (1), the thickness of the potassium tantaloniobate crystal is 0.1-5 mm.

[0013] Further, in step (1), the electrode material is one or more of Au, Ag, Cu, Fe, Al, Cr, Pt, Ti or ITO.

[0014] Further, in step (1), the electrode is deposited on the surface of the crystal by evaporation or sputtering.

[0015] Further, the ultraviolet laser is one or more mixed continuous lasers with a wavelength range of 266-405 nm.

[0016] Further, the ultraviolet laser power is 200-600 mW.

[0017] Further, the alternating electric field frequency range is 1-100 Hz, the electric field intensity is 0.5-3 kV / mm, and the cycle number is 10-50.

[0018] Further, the direction of the alternating electric field is along the growth direction of the crystal, and the voltage waveform is a triangular wave or a sinusoidal wave.

[0019] Further, the time interval between each cycle of the alternating electric field is 0-60 s.

[0020] The present application has the following beneficial effects:

[0021] The preparation method of the tetragonal transparent potassium tantaloniobate crystal provided by the present application uses the method of alternating electric field polarization under ultraviolet laser irradiation to break the micron-scale ferroelectric domains in the crystal into nanoscale polar microregions, realizes the transparency of the crystal, and the transparent state can be maintained for a long time without a large amount of thermal shock. The preparation method solves the problem that the tetragonal potassium tantaloniobate crystal cannot be applied in the field of electro-optical modulation due to low light transmittance, and also solves the problem of light scattering caused by micro-domain walls of the cubic potassium tantaloniobate crystal near the Curie point. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0023] Figure 1 is a schematic diagram of the preparation process of the tetragonal transparent potassium tantaloniobate crystal in the embodiments of the present application.

[0024] Figure 2 is a waveform curve of the alternating voltage applied in the embodiments of the present application.

[0025] Figure 3 Figure 1 is a comparison of the spectral transmittance curves of the KTN crystal before and after the alternating electric field polarization in Embodiment 1 of the present application. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should fall within the scope of protection of the present application.

[0027] Embodiment 1

[0028] A preparation method of a tetragonal phase transparent potassium tantalum niobate crystal, the specific implementation steps are as follows:

[0029] (1) Select a KTN crystal grown by the Czochralski method, the chemical formula is KTa 1-x Nb x O3, where x = 0.3, after cutting and grinding, process into a block crystal wafer of 10 x 10 x 0.1 mm 3 , wherein the direction perpendicular to the 10 mm x 10 mm plane is the crystal growth direction.

[0030] (2) Au electrodes are plated on both surfaces of the crystal 10 mm x 10 mm by using a magnetron sputtering method.

[0031] (3) Measure the dielectric temperature spectrum of the KTN crystal plated with electrodes, and obtain the Curie point of the crystal as -22℃. Control the temperature of the crystal to -28℃ and keep the temperature constant.

[0032] (4) Use an ultraviolet laser with a wavelength of 266 nm and a power of 200 mW to irradiate the crystal, and at the same time, apply a sinusoidal alternating voltage to the crystal through the electrodes for polarization; wherein the waveform of the sinusoidal alternating voltage is as shown in Figure 2 , the formed electric field strength is 0.5 kV / mm, the electric field frequency is 1 Hz, the number of cycles is 50, and the time interval between each cycle is 1 s.

[0033] After polarization, the KTN crystal changes to a transparent state. The crystal spectral transmittance curves before and after polarization are as shown in Figure 3 . The temperature of the crystal is regulated in the temperature range of -100-100℃, and the transparent state of the crystal does not change significantly.

[0034] Embodiment 2

[0035] A preparation method of a tetragonal phase transparent potassium tantalum niobate crystal, the specific implementation steps are as follows:

[0036] (1) select KTN crystal grown by Czochralski method, chemical formula KTa 1-x Nb x O3 in which x=0.5, after cutting and grinding, process into 3*4*5mm 3 Block wafer, wherein the direction perpendicular to the 3mm*4mm plane is the crystal growth direction.

[0037] (2) adopt the method of thermal evaporation film plating to plate Cu electrode on the two surfaces of the crystal 3mm*4mm.

[0038] (3) measure the dielectric temperature spectrum of the KTN crystal plated with electrode, obtain the Curie point of the crystal as 100℃, control the temperature of the crystal to 98℃ and keep constant.

[0039] (4) adopt the ultraviolet laser with wavelength of 405nm and power of 600mW to irradiate the crystal, and at the same time, apply triangular wave alternating voltage to the crystal through the electrode for polarization; the formed electric field strength is 3kV / mm, the electric field frequency is 100Hz, the cycle number is 10, and the time interval between each cycle is 60s.

[0040] After polarization, the crystal turns into transparent state. In the temperature range of-100-100℃, the temperature of the crystal is regulated, and the transparent state of the crystal does not change obviously.

[0041] Example 3

[0042] A preparation method of a tetragonal phase transparent potassium tantalum niobate crystal, the specific implementation steps are as follows:

[0043] (1) select KTN crystal grown by Czochralski method, chemical formula KTa 1-x Nb x O3 in which x=0.35, after cutting and grinding, process into 5*5*1mm 3 Block wafer, wherein the direction perpendicular to the 5mm*5mm plane is the crystal growth direction.

[0044] (2) adopt the method of ion sputtering to plate Ag electrode on the two surfaces of the crystal 5mm*5mm.

[0045] (3) measure the dielectric temperature spectrum of the KTN crystal plated with electrode, obtain the Curie point of the crystal as 14℃, control the temperature of the crystal to 11℃ and keep constant.

[0046] (4) The crystal is irradiated by ultraviolet laser with wavelength of 308 nm and power of 300 mW, and at the same time, the crystal is polarized by applying sinusoidal alternating voltage to the crystal through electrodes; the formed electric field strength is 2 kV / mm, the electric field frequency is 10 Hz, the cycle number is 30, and the time interval between each cycle is 0 s.

[0047] After polarization, the crystal is converted into a transparent state. The crystal is temperature-regulated in the temperature range of-100-100 ℃, and the transparent state of the crystal does not change obviously.

[0048] Although the present application has been described in detail with reference to the preferred embodiments, the application is not limited to the preferred embodiments. Various equivalent modifications or replacements can be made to the embodiments of the present application by those skilled in the art without departing from the spirit and essence of the present application, and these modifications or replacements shall be within the scope of the present application. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, and these changes or replacements shall be within the protection scope of the present application.

Claims

1. A method for preparing tetragonal transparent potassium tantalate niobate crystals, characterized in that, Includes the following steps: (1) Plate electrodes on the crystal surface; (2) The temperature of the potassium tantalate niobate crystal coated with electrodes is controlled to be within 2 to 6 °C below the Curie point and kept constant. (3) Polarize the crystal by applying an alternating electric field under ultraviolet laser irradiation to obtain a tetragonal transparent potassium tantalate-niobate crystal.

2. The preparation method according to claim 1, characterized in that, In step (1), the chemical formula of potassium tantalate niobate crystal is KTa. 1-x Nb x O3, where x ranges from 0.3 to 0.

5.

3. The preparation method according to claim 1, characterized in that, In step (1), the thickness of the potassium tantalate niobate crystal is 0.1 to 5 mm.

4. The preparation method according to claim 1, characterized in that, In step (1), the electrode material is one or more of Au, Ag, Cu, Fe, Al, Cr, Pt, Ti or ITO.

5. The preparation method according to claim 1, characterized in that, In step (1), the electrode is deposited on the crystal surface by evaporation or sputtering.

6. The preparation method according to claim 1, characterized in that, Ultraviolet lasers are one or more mixed continuous lasers with wavelengths ranging from 266 to 405 nm.

7. The preparation method according to claim 1, characterized in that, The ultraviolet laser power is 200–600 mW.

8. The preparation method according to claim 1, characterized in that, The alternating electric field has a frequency range of 1–100 Hz, an electric field strength of 0.5–3 kV / mm, and a number of cycles of 10–50.

9. The preparation method according to claim 1, characterized in that, The alternating electric field is directed along the direction of crystal growth, and the voltage waveform is a triangular wave or a sine wave.

10. The preparation method according to claim 1, characterized in that, The time interval between each cycle of the alternating electric field is 0 to 60 seconds.

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