几种高温压电晶体的生长、表征和性能优化研究

发布时间：2018-01-16 17:29

本文关键词：几种高温压电晶体的生长、表征和性能优化研究　出处：《山东大学》2017年博士论文　论文类型：学位论文

【摘要】：高温压电晶体材料作为压电传感器件的核心元件,被广泛应用于军工、石化、生产自控、航空航天和电力等领域。传统的陶瓷材料,例如锆钛酸铅,由于居里点温度较低、热激活老化和损耗较大等问题,实际使用温度小于600℃。商业化的单晶材料,包括石英和铌酸锂,石英存在相变,压电活性较低;铌酸锂晶体虽然具有较高压电常数和机电耦合系数,但是高温离子电导率高、电阻率低,通常使用温度低于600℃,难以满足高温环境下的应用需求。最近十几年来,硅酸镓镧结构有序晶体 Ca3TaGa3Si2O14(CTGS),稀土硼酸盐晶体 ReCa4O(BO3)3(Re:Y、Gd、Sm等稀土元素)被报道具有高熔点(1300℃～1500℃)、室温到熔点无相变、可采用提拉法生长大尺寸高质量的单晶、压电常数较大和机电性能较为突出等特点,显示了其在高温压电传感领域优良的应用前景。目前研究较多的几种高温压电晶体仍然存在一些不足,急需对性能进行更进一步的优化:(1)ReCOB硼酸盐系列晶体由于具有热释电效应,存在干扰电荷,需要对其热释电性能进行表征,为高温压电切型设计提供参考;其次单斜晶系晶体的独立电弹常数较多,需要精准测量来减小误差;压电振动存在多种模态,容易发生耦合(cross-talk),需要进行切型的优化,提升传感器件的灵敏度;研究表明该系列晶体高温压电性能存在一定的规律性,需要设计生长新晶体或者新组分的混合晶体,来进一步优化其高温压电性能。(2)CTGS晶体的电弹数据报道差异性太大,数据自洽度不够,影响了该晶体的应用,同时其高温弹性性能报道也不够全面,不能为材料模拟以及器件的设计提供一个良好的参考。(3)Ca2Nb2O7(CN)晶体具有高居里温度点,约为1575℃,可采用提拉法进行晶体生长,文献报道其陶瓷材料具有较高的电阻率和机电耦合系数,但是其晶体材料的基本热力学性能、介电、弹性、压电和铁电性能并未见报道,影响了其在压电传感方面的应用。鉴于目前以上几种高温压电晶体发展存在的问题,本论文的主要研究工作和结果如下:Ⅰ.硼酸盐系列晶体材料的晶体生长、压电性能测试表征及优化采用固相反应法合成了纯相TmCOB多晶原料,固相反应温度约为1100～1150℃。采用TDJ-J40单晶生长炉,利用Czochralski提拉技术,生长了 ReCOB(Re:Tm、Y、G 和 Sm)、YxGd1-xCa4O(BO3)3、LaxGd1-xCa4O(BO3)3、SmxY1-xCa4O(BO3)3和TmCa4O(B03)3晶体,分析和解决了晶体生长中出现的问题,最后通过高分辨X射线仪对晶体质量进行了表征。研究了 TmCOB晶体的基本热学性能,包括比热、热扩散、热膨胀和热导率,并且与同系列材料进行了比较。TmCOB晶体的热膨胀系数分别为α11=7.96×.10-6/℃,α22=4.86×10-6/℃,α33=10.32×10-6/℃。最大热膨胀方向为Z方向,最小热膨胀方向为Y方向,其热膨胀系数的比值为2.12,说明TmCOB晶体热膨胀各向异性较小。详细表征了 YCOB和TmCOB的全套电弹常数,包括介电常数、弹性常数、压电系数和机电耦合系数,并对其压电振动耦合情况(cross-talk)进行了分析,获得了不同振动模式最优化的切型。通过高温测试平台测试了 YCOB和TmCOB晶体的介电常数、介电损耗、弹性常数和压电常数的温度依赖性。在900℃时,TmCOB压电晶体具有较高的高温电阻率ρ11约为6×107Ω.cm,较低的介电损耗(tanδ2215%)。TmCOB压电常数d26为7.8 pC/N,约为石英晶体的3倍,同时其变化率小于12.9%,显示了 TmCOB晶体作为高温压电传感材料的优势。首次采用电荷积分法对ReCOB晶体的热释电性能进行了测试,并对20～180℃温度范围内的温度依赖性进行了表征。计算了热释电系数在空间上的分布,获得了无热释电效应干扰的压电切型。在室温下,ReCOB系列晶体热释电系数,约为-59.3～-65.5μC/(m2·℃),随着温度的升高,其热释电系数的绝对值减小。ReCOB具有较高的探测优值Fd,约为7.6～11.4×10-5Pa-1/2,大约是传统的热释电晶体TGS和LiTa03的两倍,说明ReCOB晶体有望在热释电探测传感领域获得应用。Ⅱ.CTGS晶体的生长、电弹性能及声波性能研究及优化采用固相反应法合成了纯相CTGS多晶原料,固相反应温度为1150～120℃。采用TDJ-J40单晶生长炉,利用Czochralski提拉技术,生长了 CTGS晶体,并且获得了较为稳定的生长工艺参数,实现了晶体的平界面生长,提高了晶体生长的良品率。通过谐振法和超声法结合测试了 32点群CTGS晶体的全套电弹常数,包括介电常数、弹性常数、压电常数和机电耦合系数,其中ε11/ε0和ε33/ε0分别为17.5和21.8,弹性刚度常数 c11、c12、c14、c13、c33、c44和 c66 分别为 15.63、7.52、8.55、0.05、22.51、4.15 和 4.06×1010N/m2,压电常数d11和 d14 分别为 4.17 和-13.7pC/N,通过旋转切型进行了数据验证,提升了数据之间的自洽度。测试了CTGS晶体介电常数随温度的变化情况,相对介电常数ε11/ε0较为稳定,在900℃时,变化率小于5%;ε33/ε0变化率大约为8.0%。在600℃,CTGS晶体的介电损耗为1.6%,比同系列的LGS晶体要小两个数量级(150%)。运用Matlab程序对其压电振动耦合进行了分析,获得了 CTGS晶体不同振动模式最优化的切型。基于全套电弹参数,我们对纯横向场激励(pure-LFE)的声波性能进行了计算分析,获得了纯横向场激励的机电耦合系数和声波速度,制作了体声波谐振器,结果显示我们设计的声波器件数据与理论数值很好的吻合。Ⅲ.CN晶体的生长、基本物理性能和压电性能研究采用固相反应法合成了纯相CN多晶原料,固相反应温度为1150～1250℃。采用不同方向籽晶生长了 CN晶体,获得了高质量的单晶材料,并且通过高分辨衍射仪进行晶体质量表征,其半峰宽小于26"。研究了 CN晶体的热学性能,其热膨胀系数为α11=5.83、α22=7.94、α33=13.32×10-6/℃,α33/α11=2.28。常温下CN晶体的热导率、热扩散和比热沿着Z方向的数值分别为3.52 W/(m·℃)、1.332 mm2/s和2.64 J/(g·℃)。热扩散系数随着温度的上升而下降,在600℃的时候变化率为-33.2%。而热导率减小为2.32 W/(m ℃),变化率为-38.1%。比热的数值随温度而减小,相对较为的稳定,变化率在温度范围内小于20%。研究了 CN晶体的结构,解析单晶衍射数据可以发现,CN晶体属于正交晶系,a=26.471A,b=5.490A,c=7.688A,晶胞体积为 1117.2A3,空间群为 Pn21a,密度为4.494 g/cm3。CN晶体具有层状的结构,畸变的钙钛矿八面体结构通过共角顶形式沿着[001]方向连接而成,而钙钛矿型结构类似的平板层沿(001)面网堆垛而成,层与层之间充填着Ca2+。而Ca08立方体彼此共棱并与Nb06八面体共棱相联。采用单晶解析的晶体结构数据,分别计算了 CN晶体Nb06八面体的畸变程度和偶极矩,Nb06八面体偶极矩的数值可以由八面体的键长、键角计算获得,单个铌氧多面体偶极矩 Nb1O6、Nb206、Nb306、Nb406分别为 3.9809、3.5934、1.2072和2.7085 debye,同时对于铌氧八面体相对应的单胞总偶极矩分别为0.028435、0.025668、0.008623 和 0.019347 debye。选取了 Z方片,经过HF酸腐蚀后,利用光学显微镜观察,发现+Z方向相比于-Z方向具有更多的腐蚀坑,并观察到了孪晶的存在,是以(100)作为公共晶面构成镜面对称的位相关系,属于无畸变的完全共格晶面。测试表征了 CN晶体的介电常数、弹性常数和压电常数,CN晶体的弹性柔顺常数与同系列的Sr2Nb207数值较为接近,其中s11=6.68 pm2/N,略大于Sr2Nb207的 5.3pm2/N;s22=9.2pm2/N,略大于 Sr2Nb207 的 9.4pm2/N。CN 晶体具有很大的相对介电常数常数,其ε22达到45.4,并且其机电耦合系数k33达到19.2%,与YCOB相当。CN晶体压电常数d31为5.8 pC/N,约为d32的两倍,压电常数d33=8.5 pC/N,约为α-SiO2的3.7倍,说明其在压电传感器领域有潜在的应用价值。测试了 CN晶体的电滞回线(@50Hz,测试电压170kv/cm),自发极化强度Ps和矫顽场Ec分别为6.5 μC cm-2和110 kv/cm。计算了其钙钛矿结构中的填充因子,约为0.832,表明Ca元素移动空间更大。
[Abstract]:High temperature piezoelectric materials as a core component of the piezoelectric sensing device, is widely used in military, petrochemical production, automation, aerospace and power fields. The traditional ceramic materials, such as lead zirconate titanate, the Curie temperature is low, the thermal activation of aging and loss of larger issues, the actual use of temperature of less than 600 degrees Celsius. Single crystal material business, including quartz and lithium niobate piezoelectric quartz, phase change, low activity; lithium niobate crystals although with a high piezoelectric constants and electromechanical coupling coefficient, but the high temperature and high ionic conductivity, low resistivity, usually use temperature lower than 600 DEG C, it is difficult to meet the application requirements under high temperature environment. In recent years, the crystal structure of Ca3TaGa3Si2O14 ordered langasite (CTGS), rare earth borate crystal ReCa4O (BO3) 3 (Re:Y, Gd, Sm and other rare earth elements) is reported with a high melting point (1300 DEG to 1500 DEG), room temperature to the melting point of no Phase change, large size and high quality single crystal growth by Czochralski method, piezoelectric constant and electromechanical properties of larger more prominent features, showing its application field of electric pressure sensor in high temperature. Several excellent high temperature piezoelectric crystal more research there are still some problems, the urgent need for further optimization of the performance: (1 ReCOB) borate based crystals with pyroelectric effect, interference charge, the need for the pyroelectric properties were characterized, and provide a reference for the high temperature piezoelectric cutting type design; secondly independent electro elastic monoclinic crystal often requires accurate measurement number to reduce the error; there are a variety of piezoelectric vibration modal, prone to coupling (cross-talk), to optimize cutting type, enhance the sensitivity of sensor devices; research showed that this series of crystal high piezoelectric properties has certain regularity, need to design new crystal growth Or a new component of the mixed crystals, further optimize its high piezoelectric properties. (2) CTGS crystal electro elastic data reported difference is too large, self consistent data is not enough, which affects the application of the crystal, and the high temperature elastic properties reported is also not comprehensive enough, can provide a good reference for the material the simulation and the design of the device. (3) Ca2Nb2O7 (CN) crystal with high Curie temperature, about 1575 degrees centigrade, for crystal growth by Czochralski method, the electrical resistivity and electromechanical coupling coefficient is reported to ceramic materials is high, but the basic thermodynamic properties of the crystal material, dielectric, piezoelectric and elastic. And ferroelectric properties was not reported, influences the application of piezoelectric sensing. In view of the above several existing problems in the development of high temperature piezoelectric crystal, the main research work and results are as follows: 1. The boric acid salt series crystal crystal Growth, characterization and optimization of piezoelectric properties of pure phase TmCOB polycrystalline materials were synthesized by solid phase reaction method, solid state reaction temperature is about 1100 ~ 1150 degrees. The TDJ-J40 single crystal growth furnace, using Czochralski Czochralski technique, ReCOB (Re:Tm, Y, the growth of G and Sm), YxGd1-xCa4O (BO3) 3, LaxGd1-xCa4O (BO3) 3, SmxY1-xCa4O (BO3) 3 and TmCa4O (B03) 3 crystal, analyze and solve the problems in crystal growth, the high resolution on the crystal quality were characterized by X ray apparatus. To study the basic thermal properties of TmCOB crystal, including specific heat, thermal diffusion, thermal expansion and thermal conductivity and, with the same series of materials were compared with.TmCOB crystal thermal expansion coefficient were alpha 11=7.96 *.10-6/ * 10-6/ C C, alpha 22=4.86, alpha 33=10.32 c * 10-6/. The maximum thermal expansion along Z direction, the minimum thermal expansion along Y direction, the coefficient of thermal expansion ratio is 2.12, indicating TmCOB crystal thermal expansion anisotropy is smaller. With a full set of electrical characterization of elastic constants of YCOB and TmCOB, including dielectric constant, elastic constants, piezoelectric constants and electromechanical coupling coefficient, and the piezoelectric vibration coupling (cross-talk) were analyzed, obtained different vibration mode optimization cutting. The dielectric the dielectric constant YCOB and TmCOB crystals were tested by high temperature test platform, dielectric loss, dependence of elastic and piezoelectric constants. The temperature is at 900 DEG C, high resistivity TmCOB piezoelectric crystal with high 11 is about 6 * 107 Omega.Cm, low dielectric loss (Tan - 2215%).TmCOB the piezoelectric constant D26 was 7.8 pC/N, about 3 times of quartz crystal, and the change rate is less than 12.9%, showing the TmCOB crystal as high temperature piezoelectric material is used for the first time. The advantages of electric charge integration method were tested on ReCOB crystal pyroelectric, and 20 to 180 degree centigrade Within the range of temperature dependence were investigated. The distribution of pyroelectric coefficient in space to calculate the free piezoelectric pyroelectric effect interference cut. At room temperature, ReCOB series crystal pyroelectric coefficient is about -59.3 ~ -65.5 ~ C/ (M2 C), with the temperature the higher the pyroelectric coefficient absolute value detection and reduce.ReCOB has a high value of Fd, which is about 7.6 ~ 11.4 * 10-5Pa-1/2, is about two times higher than the traditional pyroelectric crystal TGS and LiTa03, indicating that ReCOB crystal is expected to be used in the pyroelectric sensor domain II. The crystal growth of.CTGS electric elastic properties and acoustic performance research and optimization by solid state reaction method of pure phase CTGS polycrystalline materials synthesized by solid phase reaction temperature 1150 ~ 120 degrees. The TDJ-J40 single crystal growth furnace, using Czochralski Czochralski technique, CTGS crystal growth, and the growth parameters of relatively stable gain, The crystal plane interface growth, improve the yield of the crystal growth rate. By resonance method and ultrasonic method combined with a full set of electroelastic constants of 32 point groups of CTGS were measured, including dielectric constant, elastic constants, piezoelectric constants and electromechanical coupling coefficient, which e 11/ E 0 and E 33/ E 0 are 17.5 and 21.8, the elastic stiffness constants of C11, C12, C14, C13, C33, c44 and C66 were 15.63,7.52,8.55,0.05,22.51,4.15 and 4.06 * 1010N/m2, the piezoelectric constant D11 and D14 were 4.17 and -13.7pC/N, by rotating the cutting type of data validation, enhance the data between the self consistent degree of CTGS crystal. The dielectric constant varies with the temperature of the test, the relative dielectric constant of 11/ epsilon 0 is relatively stable, at 900 DEG C, the change rate is less than 5%; e 33/ E 0 change rate is about 8.0%. at 600 DEG C, the dielectric loss of CTGS crystal is 1.6% to two orders of magnitude smaller than the same LGS crystal series (150% ). Matlab program is used to analysis the piezoelectric vibration coupling, got cut CTGS crystals with different vibration mode optimization. A full set of electrical parameters based on the elastic, pure lateral field excitation (pure-LFE) wave was analyzed, obtained pure lateral field excitation of the electromechanical coupling coefficient and acoustic velocity that made the bulk acoustic wave resonator, results show that the acoustic wave device with the numerical data agree very well. We design of the crystal growth of.CN, the basic physical properties and piezoelectric properties of the solid phase reaction method of pure phase CN polycrystalline materials synthesized by solid state reaction temperature is 1150 to 1250 DEG C. CN crystal growth the different direction of seed crystal, the crystal of high quality material, and through high resolution diffraction for crystal quality characterization, the half peak width of less than 26. "On the thermal properties of CN crystal, the thermal expansion coefficient for alpha 11=5.8 3, alpha 22=7.94, alpha 33=13.32 * 10-6/ C, thermal conductivity of CN crystal rate of alpha 33/ alpha 11=2.28. under normal temperature, numerical along the Z direction of thermal diffusion and heat were 3.52 W/ (M - C), 1.332 mm2/s and 2.64 J/ (G - C). The thermal diffusion coefficient decreases with the increase of temperature, in when the change rate of -33.2%. and 600 DEG C conductivity decreases to 2.32 W/ (M C), the rate of change of -38.1%. value of specific heat decrease with increasing temperature, relatively stable structure, the change rate is less than 20%. in the temperature range of CN crystal research, analysis of single crystal diffraction data can be found, CN crystals are orthogonal a=26.471A, b=5.490A, c=7.688A system, cell volume is 1117.2A3, the space group is Pn21a, the density of 4.494 g/cm3.CN crystal has a layered structure, the distortion of the perovskite structure by eight corner connection form along the [001] direction and a flat layer, similar perovskite type structure along (001 Net) and stacking, between layers filled with Ca2+. and Ca08 together with Nb06 edge cube eight surface CO edge connected. Using crystal structure data of single crystal analysis, distortion degree and the dipole moment of CN crystal Nb06 eight surface are calculated, the numerical Nb06 eight surface dipole moment can be the eight surface bond length, bond angle calculation, single niobium oxide polyhedron dipole moment of Nb1O6, Nb206, Nb306, Nb406 were 3.9809,3.5934,1.2072 and 2.7085 Debye, while the total dipole moments of single cell niobium oxide eight surface corresponding to 0.028435,0.025668,0.008623 and 0.019347 respectively. Debye. Z was selected by HF film, acid corrosion after the observation by optical microscope, compared to the -Z direction has more corrosion pits found in +Z direction, and the twin is observed there is to (100) as a public plane constitute the phase relationship of mirror symmetry, no distortion is completely belongs to Lattice plane. To characterize the dielectric constant of CN crystal, elastic and piezoelectric constants, Sr2Nb207 numerical elastic compliance constants of CN crystal with the same series of approaches, including s11=6.68 pm2/N, Sr2Nb207 5.3pm2/N slightly larger than s22=9.2pm2/N, slightly larger than 9.4pm2/N.CN; Sr2Nb207 crystal has the relative permittivity constant is large, the 22 to 45.4, and the electromechanical coupling coefficient of k33 reached 19.2%, the piezoelectric constant d31 was 5.8 pC/N and YCOB.CN crystal, is about two times that of D32, the piezoelectric constant d33=8.5 pC/N, about 3.7 times as much as the alpha -SiO2, which has the potential application value in the field of piezoelectric sensor. The hysteresis loop CN crystal was tested (@50Hz, 170kv/cm, test voltage) calculated the filling factor in the perovskite structure of spontaneous polarization and coercive field strength of Ps Ec were 6.5 C cm-2 and 110 kv/cm., approximately 0.832, showed that the Ca elements move more space.

【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O78

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