准同型相界附近(Na1-xKx)0.5Bi0.5TiO3的制备及性能研究

利用固相法制备了（Na1-xKx）0.5Bi0.5TiO3系压电陶瓷，XRD分析表明所得陶瓷样品为纯的钙钛矿结构，其准同型相界在x=0．18～0．22之间；电子探针显微分析显示所做陶瓷样品晶粒发育良好，具有规则的外形和明显的晶界；实验所得陶瓷样品损耗tanδ最大不超过5％，最好的压电常数d33=153 pC／N，平面机电耦合系数kp=0．299，它们分别出现在x=0．22和0．20处。     

(Na1-xKx)0.5Bi0.5TiO3系无铅压电陶瓷的电学性能研究

利用固相法制备了(Na1-xKx)0.5Bi0.5TiO3系压电陶瓷,所得陶瓷样品介电损耗tanδ最大不超过5%,最好的压电常数d33=153pC/N,平面机电耦合系数kp=0.299,它们分别出现在x=0.22和0.20处。同时通过对其介电性能的测试,表明该样品具有弛豫铁电性,是典型的弛豫铁电体。     

Phase Transition Behavior and Electrical Properties of （1-x）K（0.5）Na（0.5）NbO3-xCa（0.3）Ba（0.7）TiO3 Lead-Free Piezoelectric Ceramics

采用固相法制备了（1–x）K0.5Na0.5NbO3–xCa0.3Ba0.7TiO3[（1–x）KNN–xCBT]系列无铅压电陶瓷,研究了CBT的含量（x=0～0.08）对样品的物相结构、显微形貌、介电性能以及压电性能的影响。结果表明：所有样品都具有钙钛矿结构;随着x的增加,室温下样品从正交相逐渐向四方相过渡并且Curie温度向低温方向移动,样品的压电常数d33与机电耦合系数kp均先升高后降低。（1–x）KNN–xCBT多晶型转变位于0.03≤x≤0.04,当x=0.03时,样品的压电性能达到最佳：d33=142 pC/N,kp=40%,其介电损耗tanδ从室温到380℃范围内几乎不变且小于0.05,表明组分为x=0.03的陶瓷是一种非常有前景的无铅压电材料。     

（1-x）Bi4Ti3O12–xK0.5Na0.5NbO3铋层状陶瓷的结构与性能

采用固相法制备（1–x）Bi4Ti3O12–xK0.5Na0.5NbO3（BIT–KNN,x=0,0.05,0.10,0.15,0.20,0.30）铋层状压电陶瓷。用X射线衍射分析及扫描电镜等测试方法研究KNN掺量与BIT–KNN陶瓷晶体结构和电性能的关系。结果表明：所有陶瓷样品均为单一的正交相结构;随着KNN掺量的增...     

（1–x）（K_（0.48）Na_（0.48）Li_（0.04））NbO_3–x（Na_（0.8）K_（0.2））_（0.5）Bi_（0.5）TiO_3无铅压电陶瓷的相变行为及其压电性能

采用固相法应法制备了（1–x）（K0.48Na0.48Li0.04）NbO3–x（Na0.8K0.2）0.5Bi0.5TiO3无铅压电陶瓷,研究了不同x（0,0.5%,1.0%,1.5%,2.0%,3.0%）对材料的相结构、介电性能以及压电性能的影响。结果表明：随着x增加,样品的Curie温度TC与正交到四方相变温度TO–T均逐渐降低,而压电常数d33与机电耦合系数kp均先升高后降低;该体系在0.5%     

Na0.5Bi0.5TiO3-Ba0.5Sr0.5Nb2O6无铅压电陶瓷的研究

采用固相法制备了(1-x)(Na0.5Bi0.5)TiO3-xBa0.5Sr0.5Nb2O6(0≤x≤1.0％)(简称(1-x)NBT-xBSN)无铅压电陶瓷,研究了不同BSN含量(x=0,0.1％,0.3％,0.5％,0.7％,1.0％,摩尔分数)样品的物相组成、显微结构及电性能.结果表明:所有样品均为纯钙钛矿结构,随掺杂量x的增加,陶瓷的相对密度pr、压电常数d33和机电耦合系数kp均先增大后降低,机械品质因子Qm和退极化温度Td则逐渐下降.该体系陶瓷具有弥散相变特征,弥散指数介于1.6～1.7.当x=0.5％时,陶瓷获得最佳性能:d33=92pC/N,kp=0.164,Qm=89,εr=650,tanδ=5.47％,pr=96.5％.     

烧结助剂CuO掺杂对0.97(K_(0.5)Na_(0.5))NbO_3–0.03Bi(Zn_(2/3)Nb_(1/3))O_3陶瓷相结构、微观形貌及电性能的影响

采用传统固相法制备了0.97(K_(0.5)Na_(0.5))NbO_3–0.03Bi(Zn_(2/3)Nb_(1/3))O_3+x CuO(KNN–3BZN–x Cu)陶瓷,探讨烧结助剂CuO对陶瓷烧结,相结构,微观形貌及电性能的影响规律。结果表明:添加CuO降低了KNN–3BZN–x Cu陶瓷的烧结温度。由于固液传质作用,陶瓷晶粒明显长大,形状发生了改变。添加CuO同时优化了陶瓷的介电性能,提高了弛豫性。KNN–3BZN–0.02Cu陶瓷在150~300℃温度范围内具有优异的电性能:介电常数εr=1 886,容温变化率–15%≤ΔC/C150℃≤15%,介电损耗tgδ0.029。同时由于体积密度大,KNN–3BZN–0.02Cu陶瓷具有较高的压电性能:d33=164 p C/N和kp=0.37。     

Relationship Between Structure and Electric Properties of （0.99–x）BNT–xBKT–0.01KNN Near Morphotropic Phase Boundary

研究了三方、四方共存[即准同型相界（morphotropic phase boundary,MPB）]附近（0.99–x）Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–0.01K0.5Na0.5NbO3[（0.99–x）BNT–xBKT–0.01KNN,x=0.16～0.23]无铅压电陶瓷的电学性能与其结构之间的变化关系。X射线衍射分析表明,随着x的增大,陶瓷材料相结构由三方相转变为四方相。当x=0.20时,（111）和（200）面衍射峰均形成劈裂峰,标志着该组分的相结构由三方–四方相共同组成,形成MPB区。样品的介电温谱表明,铁电–反铁电转变温度（Td）随着x的增大而减小,但Curie点（TC）并未明显变化。电致应变（S）随着x的增大,呈现先增加后减小的趋势,并在x=0.20时得最大值0.46%,此时动态压电系数约为575 pm/V。电滞回线显示,陶瓷样品的剩余极化强度Pr和矫顽场Ec都随着x的增大而减小,分别由41.5μC/cm2降为15.2μC/cm2和由46.5kV/cm降为15.0kV/cm,并伴随着电滞回线由扁平到束腰的形状变化,呈现从铁电相特性到反铁电相特性的转变过程。     

Na0.5Bi0.5TiO3基无铅陶瓷的铁电相变和弛豫特性研究进展

综合介绍了Na0.5Bi0.5TiO3（sodium bismuth titanate,NBT）基无铅铁电材料在铁电相变和弛豫特性方面近年来国内外的研究进展。介绍了温度变化对NBT铁电性能的影响以及产生弛豫相变的机理。此外,结合本课题的研究成果,介绍了不同含量BaTiO3和K0.5Bi0.5TiO3及其它化合物取代后对NBT基铁电相变和弛豫特性的影响。指出了在提高压电性能的同时,大幅降低材料铁电一反铁电相变,即材料的退极化温度,可能会影响到压电陶瓷材料的使用温度范围。     

烧结助剂CuO掺杂对0.97(K_(0.5)Na_(0.5))NbO_3–0.03Bi(Zn_(2/3)Nb_(1/3))O_3陶瓷相结构、微观形貌及电性能的影响

采用传统固相法制备了0.97(K0.5Na0.5)NbO3–0.03Bi(Zn2/3Nb1/3)O3+xCuO(KNN–3BZN–xCu)陶瓷,探讨烧结助剂CuO对陶瓷烧结,相结构,微观形貌及电性能的影响规律。结果表明:添加CuO降低了KNN–3BZN–xCu陶瓷的烧结温度。由于固液传质作用,陶瓷晶粒明显长大,形状发生了改变。添加CuO同时优化了陶瓷的介电性能,提高了弛豫性。KNN–3BZN–0.02Cu陶瓷在150~300℃温度范围内具有优异的电性能:介电常数εr=1886,容温变化率–15%≤ΔC/C150℃≤15%,介电损耗tgδ0.029。同时由于体积密度大,KNN–3BZN–0.02Cu陶瓷具有较高的压电性能:d33=164pC/N和kp=0.37。     

Solid state metathesis synthesis of BaTiO3, PbTiO3, K0.5Bi0.5TiO3 and Na0.5Bi0.5TiO3

A solid state metathesis approach has been applied to synthesize perovskite oxides such as BaTiO₃, PbTiO₃, K_0.5Bi_0.5TiO₃ and Na_0.5Bi_0.5TiO₃, these were characterized by powder XRD, IR and energy dispersive spectra (EDS). Potassium titanium oxalate and metal chlorides are used as the starting materials. X-ray analysis shows the formation of a single phase with tetragonal structure for BaTiO₃, PbTiO₃, K_0.5Bi_0.5TiO₃ and a monoclinic structure for Na_0.5Bi_0.5TiO₃. The Infrared spectra of these compounds show the characteristic band due to Ti–O octahedron for all the compounds. The EDS spectra show the relative ratio of the metal ions. The morphology of synthesized compounds was obtained from SEM measurements.     

Temperature-stable dielectric ceramics based on Na0.5Bi0.5TiO3

Multiple ion substitutions to Na_0.5Bi_0.5TiO₃ give rise to favourable dielectric properties over the technologically important temperature range ?55?°C to 300?°C. A relative permittivity, ε_r,?=?1300?±?15% was recorded, with low loss tangent, tanδ?≤?0.025, for temperatures from 310?°C to 0?°C, tanδ increasing to 0.05 at ?55?°C (1?kHz) in the targeted solid solution (1–x)[0.85Na_0.5Bi_0.5TiO₃–0.15Ba_0.8Ca_0.2Ti_1-yZr_yO₃]–xNaNbO₃: x?=?0.3, y?=?0.2. The ε_r-T plots for NaNbO₃ contents x?<?0.2 exhibited a frequency-dependent inflection below the temperature of a broad dielectric peak. Higher levels of niobate substitution resulted in a single peak with frequency dispersion, typical of a normal relaxor ferroelectric. Experimental trends in properties suggest that the dielectric inflection is the true relaxor dielectric peak and appears as an inflection due to overlap with an independent broad dielectric peak. Process-related cation and oxygen vacancies and their possible contributions to dielectric properties are discussed.     

Hydrothermal synthesis and characterization of Na0.5Bi0.5TiO3 microcubes

Na_0.5Bi_0.5TiO₃ microcubes with smooth faces and clear, well-defined edges have been successfully prepared for the first time by a simple hydrothermal method without any surfactants. The as-prepared Na_0.5Bi_0.5TiO₃ microcubes showed an obvious emission band compared with nanoparticles, which is attributed to the different NBT morphology and size.     

Texture development and dielectric relaxor behavior of 0.80Na0.5Bi0.5TiO3–0.20K0.5Bi0.5TiO3 ceramics templated by plate-like NaNbO3 particles

Plate-like NaNbO₃ particles were used as templates to fabricate grain-oriented 0.96(0.8Na_0.5Bi_0.5TiO₃–0.2 K_0.5Bi_0.5TiO₃)–0.04NaNbO₃ (NKBT) ceramics. The effects of the sintering temperature and the soaking time on the grain orientation and the microstructure of the textured NKBT ceramics were investigated, and the dielectric relaxor behavior is discussed. The results show that textured ceramics were successfully obtained with orientation factor more than 0.8. The textured ceramics have a microstructure with strip-like grains aligning in the direction parallel to the casting plane. The degree of grain orientation increases initially, then decreases with increasing sintering temperature, and increases continuously with increasing soaking time. The textured NKBT ceramics shows obvious dielectric relaxor characteristics which can be well explained by microdomain–macrodomain transition theory with calculating criterion K. The results show that formation of texture is beneficial to microdomain–macrodomain transition, which lead to weaken relaxor behavior and raise the dielectric constant at T_tr.     

Dielectric and optical properties of Ni doped Na0.5Bi0.5TiO3

Polycrystalline Ni doped Na_.5Bi_0.5TiO₃ samples (Na_0.5Bi_0.5)Ti_1-xNi_xO_3, (x?=?0.5, 0.10, 0.15) have been prepared by solid state reaction. The appearance of the additional peak in X-ray diffraction pattern indicates the ordering of Ti⁴⁺ and Ni²⁺ ions. Polygonal grains are converted into flakes with an increase of Ni concentration. Replacement of Ti⁴⁺ by Ni²⁺ strongly modifies the relative contribution of two peaks in the Raman bands within 200–400?cm^?1. Oxygen vacancy is observed in X-ray photoelectron spectrum to maintain charge neutrality due to aliovalent doping. Broad diffuse phase transition centered at the dielectric constant maximum indicates relaxor behaviour. Comparison between impedance and electric modulus spectrum suggests non-Debye relaxation. The ac conductivity follows the power law with the frequency exponent lies 0.52???0.72. The generation of holes by divalent Ni dopant at tetravalent Ti sites enhances optical band gap.     

Dielectric stability in the relaxor: Na0.5Bi0.5TiO3-Ba0.8Ca0.2TiO3-Bi(Mg0.5Ti0.5)O3- NaNbO3 ceramic system

Ceramics with temperature-stable dielectric characteristics have been developed in the system: 0.6[0.85Na_0.5Bi_0.5TiO₃-(0.15-x)Ba_0.8Ca_0.2TiO₃-xBi(Mg_0.5Ti_0.5)O₃]?0.4NaNbO₃, x ≤ 0.15. Dielectric measurements exhibited relaxor ferroelectric characteristics with temperature-stable relative permittivity from ε_r~1330 ± 15% in the temperature range from ?70?°C to 215?°C and tanδ ≤ 0.02 from ?20?°C to 380?°C for x = 0 compositions. For the Bi(Mg_0.5Ti_0.5)O₃ modified compositions the temperature range of stable relative permittivity extended from ?70?°C to 400?°C, with ε_r ~ 950 ± 15% and tanδ ≤ 0.02 from ?70?°C to 260?°C. Values of dc resistivity were ~ 10⁸ Ω?m at a temperature of 300?°C and the corresponding RC constant values were in the range from 0.40 ? 0.78?s at 300?°C. All ceramic samples exhibited a linear polarisation-electric field response at maximum applied electric field of 5?kV/cm (1?kHz).     

Complex structural contribution of the morphotropic phase boundary in Na0.5Bi0.5TiO3 - CaTiO3 system

The correlation between structure and dielectric properties of lead-free (1-x)Na_0.5Bi_0.5TiO₃ - xCaTiO₃ ((1-x)NBT - xCT) polycrystalline ceramics was investigated systematically by X-ray diffraction, combined with impedance spectroscopy for dielectric characterizations. The system shows high miscibility in the entire composition range. A morphotropic phase boundary (MPB), at 0.09?≤?x?<?0.15 was identified where rhombohedral and orthorhombic symmetries coexist at room temperature. The fraction of orthorhombic phase increases gradually with x in the MPB region. Dielectric measurements reveal that the relative permittivity increase with addition of Ca²⁺. This behavior is unusual with this kind of doping. A thermal hysteresis occurred only in the MPB composition which varies in a non-monotonically manner with x, detected by dielectric properties. This phenomenon is related to the crystalline microstructure by a linear relationship between the fraction of each phase and dielectric properties, and, more precisely, to the strong interaction between rhombohedral and orthorhombic phases.     

Sr和Mn复合掺杂(Na0.8K0.2)0.5Bi0.5TiO3无铅压电陶瓷

用固相法制备了(Na0.8K0.2)0.5Bi0.5TiO3+xmol%SrCO3+xmol%MnCO3(0≤x≤1.25%)(简称NKBTSM)无铅压电陶瓷,用XRD、SEM、Agilent 4294A精密阻抗仪等对该体系陶瓷的结构与电性能进行表征。结果表明:所制备的NKBTSM陶瓷样品均为单一的钙钛矿结构。Sr和Mn的复合掺杂促进了晶粒的长大,并提高了致密度。与纯NKBT陶瓷相比,掺杂Sr和Mn能提高陶瓷的压电常数d33、机电耦合系数kp和机械品质因子Qm,降低陶瓷的介质损耗tanδ。该系陶瓷具有介电弛豫特性,弥散因子随x的增加先增大后减小。综合考虑:x=1.00%陶瓷的电学性能最佳:d33=152pC/N,Qm=195,kp=28.66%,εr=701,tanδ=2.84%。     

Effect of different templates on microstructure of textured Na0.5Bi0.5TiO3–BaTiO3 ceramics with RTGG method

One-dimensional needle-like KSr₂Nb₅O₁₅ (KSN) and two-dimensional plate-like Bi_2.5Na_3.5Nb₅O₁₈ (BNN) particles were used as templates to fabricate grain-oriented Na_0.5Bi_0.5TiO₃–BaTiO₃ (NBTBT) ceramics by reactive-templated grain growth. The effects of the template concentration on the microstructure and orientation of NBTBT ceramics were investigated, and the mechanism of grain growth was discussed. The results show that NBTBT textured ceramics cannot be obtained with KSN template, since the needle-like KSN particles were aligned randomly along the tape casting direction. Ceramics contain perovskite NBTBT and tungsten–bronze-type KSN phase. Some cucurbit-like KSN grains resulted from the defects of needle-like KSN templates were detected. Textured ceramics with orientation factor more than 60% were obtained successfully when the plate-like BNN was used as templates. The results show that the texture fraction of NBTBT textured ceramics increase with increasing the content of BNN. The textured ceramics exhibited {h 0 0} preferred orientation have brick wall microstructure with strip-like grains aligning in the same plane as the casting plane. The reaction and crystal formation of textured NBTBT ceramics with plate-like BNN templates are by diffusion–recrystallization process. Finally the selecting rules of suitable templates are proposed.     

Fabrication and electrical properties of textured (Na,K)0.5Bi0.5TiO3 ceramics by reactive-templated grain growth

Textured (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) ceramics with a relative density of >94% were fabricated by reactive-templated grain growth. Plated-like Bi₄Ti₃O₁₂ template particles synthesized by the NaCl–KCl molten salt process were aligned by tape casting in a mixture of original oxide powders. The effect of sintering temperature on the grain orientation and electrical properties of textured NKBT ceramics were investigated. The results show that the textured ceramics have a microstructure with plated-like grains aligning in the direction parallel to the casting plane. The degree of grain orientation increased at increasing sintering temperature. The textured ceramics show anisotropic electrical properties in the directions parallel and perpendicular to the casting plane. The dielectric constant parallel to {h 0 0} plane is three times higher than that of the perpendicular direction in textured NKBT ceramics. The optimized sintering temperature is 1150 °C where the maximum dielectric constant is 2041, the remnant polarization is 68.7 μC/cm², the electromechanical coupling factor (k₃₁) and the piezoelectric constant (d₃₃) amount to 0.31 and 134 pC/N, respectively.