(Sr,Ca)TiO3陶瓷材料的结构与介电性能

研究(Sr,Ca)TiO_3系统陶瓷材料的组成、结构与介电性能关系.当ST/CT比值约为7:3时,主晶相(Sr_(0.7)Ca_(0.3))TiO_3形成完全互溶钙钛矿型固溶体,具有立方顺电相结构;系统中微量钨青铜型新化合物铌酸钛钡BTN对主晶相(Sr_(0.7)Ca_(0.3))TiO_3的介电性能起进一步的改善作用.获得具有理想介电性能(ε(20℃1MHZ)>250,αc(-55～+125℃)=-1150ppm/℃,tgδ(20℃1MHZ)<5×10-4,ρv(20℃100VDC)>1013Ω·cm)、不含Pb、Bi的Q组MLC瓷料.     

Zn_2SnO_4掺杂对BaTiO_3陶瓷介电性能的影响

用固相反应法分别合成了Zn2SnO4、BaTiO3粉体,用传统陶瓷制备工艺制备了Zn2SnO4掺杂的BaTiO3陶瓷(ZS-BT),研究了掺杂量变化对BaTiO3陶瓷介电性能的影响。研究发现,适量的Zn2SnO4掺杂可促进BaTiO3陶瓷的烧结,降低BaTiO3陶瓷的介电损耗;随着掺杂量的增加,BaTiO3陶瓷的介电居里峰逐渐降低弥散,并向低温方向移动;在测量频率范围内(102~109 Hz),Zn2SnO4掺杂使得介温曲线在40~125℃温度区间内变得平坦,当Zn2SnO4的掺杂比例为2%时,介电常数变化率低于8%。这些结果表明,ZS-BT陶瓷对研究温度稳定性良好的陶瓷电容器有着重要的意义。     

添加剂MnCO_3和BazrO_3对Ba(Zn_(1/3) Nb_(2/3))O_3陶瓷烧结温度和介电性能的影响

采用传统的固相烧结法制备Ba(Zn_(1/3) Nb_(2/3))O_3(BZN)和(1-x)Ba(Zn_(1/3)Nb_(2/3))O_3-xSr(Zn_(1/3)Nb_(2/3))O_3(BSZN)陶瓷,研究MnCO_3和BaZrO_3添加剂对其烧结温度和介电性能的影响。研究表明二者均是很好的助熔剂,在烧结过程中形成液相促进原子扩散从而降低烧结温度,本研究中的最佳烧结温度为1260℃(5#样品)。MnCO_3和BaZrO_3对于改善系统的介电性能均有较好的效果,合理调整添加剂的用量可以有效的改善介电性能。0.35BZN-0.65SZN-1%MnCO_3样品的介电性能最佳且烧结温度低于1300℃。     

Dy掺杂BaTiO3陶瓷的制备及其介电性能

采用溶胶凝胶法制备了掺杂不同量Dy2O3(掺杂摩尔分数分别为0.001,0.002,0.003,0.005,0.007)的BaTiO3陶瓷,并对其介电性能的变化进行了研究.结果表明Dy2O3掺杂使BaTiO3陶瓷的电阻率明显降低,当添加量为0.005mol时,电阻率最小,为4.19×108Ω·m.Dy2O3掺杂使BaTiO3陶瓷的介电性能在不同掺杂量和不同频率下发生了明显变化,掺杂量为0.001mol、0.002mol时,BaTiO3陶瓷的介电特性和频率特性得到明显改善,在频率为1000Hz时介电性能相对较好.Dy2O3掺杂使BaTiO3陶瓷的介电温谱有所展宽,且Curie温度有所降低,交流电导随着温度的升高而增大,并在Curie点附近达到最高.     

(Sr,Ca)TiO3陶瓷材料的结构与介电性能

研究(Sr,Ca)TiO₃系统陶瓷材料的组成、结构与介电性能关系.当ST/CT比值约为7:3时,主晶相(Sr_0.7Ca_0.3)TiO₃形成完全互溶钙钛矿型固溶体,具有立方顺电相结构;系统中微量钨青铜型新化合物铌酸钛钡BTN对主晶相(Sr_0.7Ca_0.3)TiO₃的介电性能起进一步的改善作用.获得具有理想介电性能(ε_(20℃1MHZ)>250,α_{c(-55～+125℃)}=-1150ppm/℃,tgδ_(20℃1MHZ)<5×10^-4,ρ_{v(20℃100VDC)}>10¹³Ω·cm)、不含Pb、Bi的Q组MLC瓷料.     

(Ba1-xCax)(Ti0.82Zr（0.18）)O3陶瓷结构与介电性能研究

采用固相反应法制备了(Ba1-xCax)(Ti0.82Zr0.18)O3(BCZT,0≤x≤0.26)陶瓷,研究了Ca2+掺杂对BCZT陶瓷微观结构和介电性能的影响.结果表明:当Ca2+掺杂量为0.16时,BCZT陶瓷出现第二相CaTiO3,其四方率c/a随Ca2+掺杂量的增加先减小再增大,当Ca2+掺杂量为0.06时达到最小值1.00276.通过容差因子和晶格参数的计算确认了Ca2+已进入到A位;随Ca2+掺杂量的增加,晶粒得到细化,居里温度向低温方向移动,介电峰被压低并展宽,且逐渐呈现铁电弥散性.     

MnCO3/MnO2共掺杂对（Ba,La,Ca）TiO3基陶瓷材料介电性能的影响

采用水热法制备了Ba0.7La0.2Ca0.1TiO3陶瓷材料,研究了MnCO3/MnO2共掺杂对陶瓷材料介电性能的影响及相关的影响规律。随着nMnCO3/nMnO2的增加,材料的介电常数开始增大随后减小,而介电损耗先减小再增大后开始波动,击穿场强先增大后减小。当nMnCO3/nMnO2为3∶1时介电常数最大,得到了介电常数(εr)为4661,介质损耗(tanδ)为0.0165,击穿场强(Eb)为12.58kV/mm,绝缘电阻(R)为3.7×1013Ω的高介电低损耗陶瓷粉体材料。最后探讨了MnCO3/MnO2共掺杂改性的有关机理。     

Al2O3掺杂BaTi0.85Sn0.15O3陶瓷的制备及性能表征

通过传统固相二次烧结法来制备x wt% Al₂O₃（x=0、1.0、1.5）/BaTi_0.85Sn_0.15O₃（BTS）陶瓷。研究了掺杂不同含量Al₂O₃对BTS陶瓷的微观结构、介电性能及挠曲电性能的影响。结果表明,掺杂Al₂O₃的BTS陶瓷不改变陶瓷的晶体结构,仍为标准钙钛矿结构晶型;Al₂O₃的掺入能够有效降低晶粒尺寸,具有明显的细晶作用。随着Al₂O₃含量的增大,Al₂O₃/BTS陶瓷的介电常数减小,介电损耗得到明显改善,居里峰逐渐宽化且向温度高的方向偏移。Al₂O₃/BTS陶瓷的挠曲电系数随着Al₂O₃含量的增加和测试环境温度的升高均减小。此外,Al₂O₃/BTS陶瓷的挠曲电系数和介电常数之间存在一种近线性关系,但当温度非常接近于居里温度时,这种线性关系减弱。     

温度稳定型Pb(Ni1/3Nb2/3)O3基复相陶瓷的制备及介电性能

选取居里温度不同的两组元,对其中一组元包覆PT,再与另一组元混合烧结,制备出满足X7R温度稳定特性的复相陶瓷用TEM观察了PT包覆前后粉末的颗粒形态,结果表明,PT较好地附着在颗粒表面.PT包覆层的存在抑制了两相的固溶反应,使材料保持复相结构,改善了材料的介电温度特性.分析了PT包覆层的作用.     

溶胶凝胶法制备钛酸锶钡(Ba1-xSrx)TiO3陶瓷及其介电性能的研究

采用硝酸钡、硝酸锶、钛酸丁酯和柠檬酸为原料的配合物溶胶凝胶方法制备了(Ba1-xSrx)TiO3(BST)陶瓷.实验结果表明,BST粉体合成温度及烧结温度分别为700及1250℃,均低于传统工艺的相应温度. Sr含量x≥0.40,(Ba1-xSrx)TiO3陶瓷的相结构为立方钙钛矿相;Sr含量x＜0.40,(Ba1-xSrx)TiO3陶瓷的相结构为四方钙钛矿型. (Ba1-xSrx)TiO3(0.5≤x≤0.70)陶瓷的电容率随温度变化曲线,说明存在由铁电四方相到顺电立方相的相变.且随锶(Sr)的摩尔量x的增加,(Ba1-xSrx)TiO3陶瓷样品的相变温度向低温方向移动,相变温度Tc的移动关系为Tc=394.1-272.6x(K).     

Single-phase formation mechanism and dielectric properties of sol-gel-derived Ba(Ti0.2Zr0.2Sn0.2Hf0.2Ce0.2)O3 high-entropy ceramics

Single-phase Ba(Ti_0.2Zr_0.2Sn_0.2Hf_0.2Ce_0.2)O₃(BTZSHC) high-entropy ceramics(HECs) with the perovskite structure were successfully prepared via the sol-gel method.The results reveal that the as-prepared ceramics exhibit a single cubic phase belonging to the Pm3 m space group.The high entropy is the driving force of the formation of single-phase ceramics.A larger entropy(ΔS_mix) and a negative enthalpy(ΔH_mix) are...     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by Substituting Mg for Co

The microwave dielectric properties of La(Mg_0.5−xCo_xSn_0.5)O₃ ceramics were examined with a view to exploiting them for mobile communication. The La(Mg_0.5−xCo_xSn_0.5)O₃ ceramics were prepared using the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La(Mg_0.4Co_0.1Sn_0.5)O₃ ceramics revealed that La(Mg_0.4Co_0.1Sn_0.5)O₃ is the main crystalline phase, which is accompanied by small extent of La₂Sn₂O₇ as the second phase. Formation of this Sn-rich second phase was attributed to the loss of MgO upon ignition. Increasing the sintering temperatures seemed to promote the formation of La₂Sn₂O₇. An apparent density of 6.67 g cm⁻³, a dielectric constant (?_r) of 20.3, a quality factor (Q.F.) of 70,500 GHz, and a temperature coefficient of resonant frequency (τ_f) of −77 ppm °C⁻¹ were obtained for La(Mg_0.4Co_0.1Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Magnetic properties of La and (La, Zr) doped BiFeO3 ceramics

Bi_0.9La_0.1FeO₃ (BLF) and Bi_0.9La_0.1Fe_0.98Zr_0.02O₃ (BLFZ) ceramics were synthesized by conventional solid state reaction method. X-ray diffraction studies and Rietveld refinements indicated that both of the samples possessed rhombohedrally distorted perovskite structure. The average grain size of BLFZ (~700 nm) was greatly reduced in comparison with BLF (~6 μm). The remanent magnetization of BLFZ was greatly enhanced compared with BLF. The enhancement of remanent magnetization was attributed to the collapse of the spiral spin structure. Both samples showed exchange bias. The possible reason for the appearance of exchange bias was attributed to the inhomogeneity in doping. The measurements of magnetization as a function of temperature indicated that BLF and BLFZ had almost the same magnetic transition temperature (~355 °C).     

Phase transition characteristics and dielectric properties of rare-earth (La,Pr, Nd,Gd) doped Ba(Zr0.09Ti0.91)O3 ceramics

A-site deficient rare-earth doped barium zirconate titanate (BZT) ceramics (Ba_1−yLn_2y/3)Zr_0.09Ti_0.91O₃ (Ln = La, Pr, Nd, Gd) are obtained by a modified solid-state reaction method. Perovskite-like single-phase compounds were confirmed from X-ray diffraction data. Morphological analysis on sintered samples shows that the addition of rare-earth ions inhibits the growth of the grain and remarkably changes the grain morphology. The effect of rare-earth addition to BZT on phase transition and dielectric properties is analyzed. A dramatic fall in the transition temperature occurs when BZT ceramic is doped with rare-earths. Moreover, diffusivity degree of the phase transition increases and a relaxor-type behaviour is induced due to both the increment of the lanthanide content and the increase of the ionic radius of the dopant element. High values of dielectric tunability are obtained for lanthanum doped BZT. A direct relation between transition temperature and tunability is discussed. Conclusively, low permittivity and high tunability materials can be obtained by the adequate substitution of rare-earths into BZT ceramics.     

Modified (K0.5Na0.5)(Nb0.9Ta0.1)O3 ceramics with high Qm

Lead-free ceramics (K_0.5Na_0.5)(Nb_0.9Ta_0.1)O₃ (KNNT) + x mol% K₄CuNb₈O₂₃ (KCN) + y mol% MnO₂ have been prepared using the conventional solid-state reaction technique. Crystalline structures and Microstructures were analyzed by X-ray diffraction and scanning electron microscope (SEM) at room temperature. The low dielectric loss tanδ and relatively high piezoelectric properties were obtained when KCN and MnO₂ were added into KNNT ceramics. The ceramics with x = 1.0, y = 0.50 exhibited excellent piezoelectric properties: high mechanical quality factor Q_m = 1563, piezoelectric coefficient d₃₃ = 96pC/N, electromechanical coupling coefficient k_p = 42.2%, k_t = 44.5%, k₃₃ = 58.4%, relative dielectric constant ε′ = 308, tanδ = 0.4%. This material is a promising candidate for the lead-free piezoelectric transformer applications.     

Dielectric properties of (Ba,Nb) doped TiO2 ceramics: Migration mechanism and roles of (Ba,Nb)

Ultrahigh relative dielectric constants with stable frequency and temperature dependence as well as relatively low loss tangent are found in barium and niobium doped TiO₂ ceramics with a silver electrode. The roles of barium and niobium on the dielectric properties of the ceramics are explained after the migration mechanism and the influence of barium and niobium have been analysed. Both silver electrodes made from silver paste and evaporated aluminium electrodes are employed in the study, their effects are also discussed. The migration mechanism proposed is electron hopping among oxygen vacancies. Dissolving barium into TiO₂ ceramics creates an additional oxygen vacancy which results in an increase in conductivity and relaxation frequency of the loss tangent. In contrast, niobium tends to reduce the concentration of oxygen vacancies and causes the opposite effect. The effects of barium and niobium on the concentration of the oxygen vacancy are supported by results of densification and microstructural investigations.     

Influence of Ca0.8Sr0.2TiO3 on the microstructures and microwave dielectric properties of Nd(Mg0.4Zn0.1Sn0.5)O3 ceramics

The influence of Ca_0.8Sr_0.2TiO₃ on the microstructures and microwave dielectric properties of Nd(Mg_0.4Zn_0.1Sn_0.5)O₃ ceramics were investigated by the conventional solid-state method. The X-ray diffraction peaks of (1 − x)Nd(Mg_0.4Zn_0.1Sn_0.5)O₃–xCa_0.8Sr_0.2TiO₃ ceramic system shifted to higher angles as x increased. The dielectric constant increased from 31.8 to 47.7, the quality factor (Q × f) decreased from 54,200 to 42,800 GHz, and the temperature coefficient of resonant frequency (τ _f ) increased from −43 to +41 ppm/°C as x increased from 0.5 to 0.7 when (1 − x)Nd(Mg_0.4Zn_0.1Sn_0.5)O₃–xCa_0.8Sr_0.2TiO₃ ceramic system sintered at 1,600 °C for 4 h.     

Fabrication of One-Transistor-Capacitor Structure of Nonvolatile TFT Ferroelectric RAM Devices Using Ba(Zr 0.1Ti 0.9)O 3 Gated Oxide Film

In this study, the Ba(Zr_0.1Ti_0.9)O₃ (BZ1T9) thin films have been well deposited on the Pt/Ti/SiO₂/Si substrate. The optimum radio frequency (RF) deposition parameters are developed, and the BZ1T9 thin films deposition at the optimum parameters have the maximum capacitance and dielectric constant of 4.4 nF and 190. As the applied voltage is increased to 8 V, the remnant polarization and coercive field of BZ1T9 thin films are about 4.5 muC/cm² and 80 kV/cm. The counterclockwise current hysteresis and memory window of n-channel thin-film transistor property are observed, and that can be used to indicate the switching of ferroelectric polarization of BZ1T9 thin films. One-transistor-capacitor (1TC) structure of BZ1T9 ferroelectric random access memory device using bottom-gate amorphous silicon thin-film transistor was desirable because of the smaller size and better sensitivity. The BZ1T9 ferroelectric RAM devices with channel width = 40 mum and channel length = 8 mum has been successfully fabricated and the I_D-V_G transfer characteristics also are investigated in this study.     

Yttrium-doped effect on thermoelectric properties of La0.1Sr0.9TiO3 ceramics

Ceramic samples of La_0.1Y _x Sr_0.9–x TiO₃ with different yttrium concentration have been synthesized by conventional solid state reaction technique, and their thermoelectric properties have been investigated. X-ray diffraction characterization confirms that the main crystal structure is of perovskite, but with a small amount of second phase of Y₂Ti₂O₇ for samples with x = 0.05, 0.08, and 0.10. SEM images indicate all ceramic samples are dense and compact, and the largest grain size appears in sample with x = 0.03 and 0.05. Also the second phase can also be identified from the SEM images for x = 0.05, 0.08, and 0.10 samples. Electrical conductivity and Seebeck coefficient of samples have been measured in the temperature range between 300 and 1100 K. With increasing of yttrium concentration, electrical resistivity decreases, and reaches 0.8 mΩ cm for x = 0.10 sample at room temperature. The absolute Seebeck coefficients increase monotonically with increasing temperature in the whole temperature range. Sample with x = 0.03 exhibits the highest absolute Seebeck coefficient 219 μV K⁻¹ at 1059 K, as well as the maximum power factor 11 μW cm⁻¹ K⁻² at 624 K.     

预烧温度对BZN微波陶瓷介电性能的影响

以工业纯BaCO3、ZnO、Nb2O5为原料,按照一定配比配料混合,通过传统的固相反应法合成Ba(Zn1/3Nb2/3)O3(即BZN)陶瓷材料,预烧温度(分别为1000、1100和1200℃)对BZN陶瓷微波性能的影响过程中,对合成的BZN粉体进行差热/热重分析,对烧结后的BZN陶瓷进行XRD分析和SEM形貌观察,利用矢量网络分析仪测量BZN陶瓷的微波性能Q、εr和rf.实验结果表明,预烧温度对BZN微波陶瓷的介电性能影响比较大,预烧温度为1200℃时可以获得较好的介电性能εr=41.6,Q*f=38671GHz,τf=2.8×105/℃.