Na0.25K0.25Bi0.5TiO3无铅压电陶瓷的介电特性研究

用固相反应法制备了Na_0.25K_0.25Bi_0.5TiO₃ (NKBT50)陶瓷，研究了该陶瓷在室温至400℃温度范围内的介电性能.发现该陶瓷的介电温谱与烧结气氛、极化状态有关.在空气中烧结的未极化样品在70℃附近存在介电和损耗峰，而极化后及在氧气氛中烧结的样品并不存在该介电、损耗峰.分析认为70℃的介电和损耗峰与氧空位形成的缺陷偶极子的极化弛豫有关.热激电流显示，陶瓷的去极化温度为225℃，与此相对应的介电、损耗峰也 关键词： 介电性能 氧空位 极化弛豫 钛酸铋钠钾     

Large piezoresponse of lead-free Bi0.5(Na0.85K0.15)0.5TiO3 thin film

0.85Bi_0.5Na_0.5TiO₃-0.15Bi_0.5K_0.5TiO₃ (BNKT15) lead-free thin films were prepared on Pt(111)/TiO₂/SiO₂/Si(100) substrates by the chemical solution deposition method. BNKT15 are MPB composition in the Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃ (BNT-BKT) system. The maximum piezoelectric coefficient (d_33,f) value of BNKT15 thin film is approximately 75 pm/V, which is comparable to that of polycrystalline PZT thin films. These results suggest that BNKT15 thin film can be used as an alternative for PZT films in piezoelectric micro-electromechanical systems.     

Site occupation of doping La3+ cations and phase transition in Na0.5Bi0.5TiO3–BaTiO3 solid solution

The effects of La doping on the ferroelectric properties of 0.92Na0.5Bi0.5TiO3-0.08BaTiO3(NBT-BT) solid solution have been studied both experimentally and theoretically.The experimental results show that an abnormal ferro-toantiferroelectric phase transition is induced by La doping in NBT-BT.The first-principles calculations indicate that La3+ cations selectively substitute for the A site in NBT-BT as donors.Furthermore,the computed binding energy reveals that La cations is most likely to substitute Ba 2+or Na+,not Bi3+,at A site as donors in NBT-BT,as supported by our Raman spectra.The ferro-to-antiferroelectric phase transition of La-doped NBT-BT is believed to originate from the lattice aberrance and redistribution of valence electrons,thus strengthening the bonding of A-O,enhancing the hybridization between the A cation d orbital and O 2p orbital,and resulting in the deflection of the polar direction of NBT-BT lattice.     

Thickness-dependent tunable characteristics of (Ba0.5Sr0.5)0.925K0.075TiO3 thin films prepared by pulsed laser deposition

The thickness-dependent dielectric properties and tunability of pulsed laser deposited (Ba_0.5Sr_0.5)_0.925K_0.075TiO₃ (BSKT) thin films with different thickness ranging from 80 to 300 nm has been investigated. Dielectric properties of the BSKT thin films are substantially improved as the BSKT film thickness increases, which can be explained by the model of a low-permittivity dead layer that is connected in series with the bulk region of the film. The estimated values of thickness and the average dielectric constant for the dead layer are 2.4 nm and 23.5, respectively, in a Pt/BSKT/Pt capacitor structure. The tunability and figure of merit increased with increasing film thickness, which are attributed to the change in lattice parameter and the dead layer effect.     

Sol-gel法制备Bi0.85Nd0.15FeO3多铁性薄膜

利用sol-gel法在Pt/Ti/SiO₂/Si衬底上制备出Bi_0.85Nd_0.15FeO₃薄膜.研究退火温度对其晶相形成的影响,发现在450 ℃退火时,Bi_0.85Nd_0.15FeO₃晶相开始形成,但是结晶较差,而且存在杂相;在500—600 ℃退火可以获得单相Bi_0.85Nd_0.15FeO₃薄膜,退火温度升高有利于其结晶.对600 ℃退火的Bi_0.85Nd_0.15FeO₃薄膜的介电、铁电和电磁性能进行了测试.在测试频率为1 MHz时,其介电常数和介电损耗分别为145,0.032;饱和磁化强度大约为44.8 emu/cm³;剩余极化值(2P_r)大约是16.6 μC/cm². 关键词： sol-gel法 0.85Nd_0.15FeO₃薄膜')" href="#">Bi_0.85Nd_0.15FeO₃薄膜 铁电性能 铁磁性能     

Structure, ferroelectric and piezoelectric properties of (Bi1−x−yNa0.925−x−yLi0.075)0.5BaxSryTiO3 lead-free piezoelectric ceramics

Lead-free multi-component ceramics (Bi_1−x−yNa_{0.925−x−y}Li_0.075)_0.5Ba_xSr_yTiO₃ have been prepared by an ordinary sintering technique and their structure and electrical properties have been studied. All the ceramics can be well-sintered at 1100 °C. X-ray diffraction patterns shows that Li⁺, Ba²⁺ and Sr²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) is formed at 0.04 < x < 0.08. As compared to pure Bi_0.5Na_0.5TiO₃ ceramic, the coercive field E_C of the ceramics decreases greatly and the remanent polarization P_r of the ceramics increases significantly after the formation of the multi-component solid solution. Due to the MPB, lower E_C and higher P_r, the piezoelectricity of the ceramics is greatly improved. For the ceramics with the compositions near the MPB (x = 0.04–0.08 and y = 0.02–0.04), piezoelectric coefficient d₃₃ = 133–193 pC/N and planar electromechanical coupling factor k_P = 16.2–32.1%. The depolarization temperature T_d reaches a minimum value near the MPB. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both the polar and non-polar regions at temperatures near/above T_d.     

Microwave dielectric properties of (1 − x)(Mg0.95Co0.05)TiO3–x(Na0.5La0.5)TiO3 ceramic system

The microstructures and the microwave dielectric properties of the (1 − x)(Mg_0.95Co_0.05)TiO₃–x(Na_0.5La_0.5)TiO₃ ceramic system were investigated. Two-phase system was confirmed by the XRD patterns and the EDX analysis. A co-existed second phase (Mg_0.95Co_0.05)Ti₂O₅ was also detected. The microwave dielectric properties are strongly related to the density and the matrix of the specimen. A new microwave dielectric material 0.88(Mg_0.95Co_0.05)TiO₃–0.12(Na_0.5La_0.5)TiO₃, possessing an excellent combination of dielectric properties: ε_r  22.36, Q × f  110,000 GHz (at 9 GHz), τ_f  2.9 ppm/°C), is proposed as a candidate dielectric for GPS patch antennas.     

The effect of Si surface nitridation on the interfacial structure and electrical properties of (La2O3)0.5(SiO2)0.5 high-k gate dielectric films

Thermal stability, interfacial structures and electrical properties of amorphous (La₂O₃)_0.5(SiO₂)_0.5 (LSO) films deposited by using pulsed laser deposition (PLD) on Si (1 0 0) and NH₃ nitrided Si (1 0 0) substrates were comparatively investigated. The LSO films keep the amorphous state up to a high annealing temperature of 900 °C. HRTEM observations and XPS analyses showed that the surface nitridation of silicon wafer using NH₃ can result in the formation of the passivation layer, which effectively suppresses the excessive growth of the interfacial layer between LSO film and silicon wafer after high-temperature annealing process. The Pt/LSO/nitrided Si capacitors annealed at high temperature exhibit smaller CET and EOT, a less flatband voltage shift, a negligible hysteresis loop, a smaller equivalent dielectric charge density, and a much lower gate leakage current density as compared with that of the Pt/LSO/Si capacitors without Si surface nitridation.     

Effect of different annealing methods on ferroelectric properties of 0.95Pb(Sc0.5Ta0.5)O3-0.05PbTiO3 thin films

0.95Pb(Sc_0.5Ta_0.5)O₃-0.05PbTiO₃ thin films were prepared on LaNiO₃/SiO₂/Si substrate by radio frequency magnetron sputtering, and the films were annealed subsequently with repeated many times by two approaches: normal one-step rapid thermal annealing and innovative two-steps rapid thermal annealing. X-ray diffraction demonstrates that all the films were preferred (1 0 0) oriented and an appropriate repeat of annealing process can enhance perovskite phase of the films. Scanning electron microscopy suggests that the films treated by two-steps rapid thermal annealing show crack-free, uniform size grains and dense microstructure. Measurement of remnant polarization and leakage current dependence of electric field confirms that the films treated by two-steps rapid thermal annealing exhibit better ferroelectric properties than the films treated by one-steps rapid thermal annealing. The results reveal that microstructure plays an important role in enhanced ferroelectric properties of the 0.95Pb(Sc_0.5Ta_0.5)O₃-0.05PbTiO₃ thin films.     

Effects of Li2CO3 on the sintering behavior and piezoelectric properties of Bi2O3-excess (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics doped with Li₂CO₃ and Bi₂O₃ as sintering aids were manufactured, and their micro structural, dielectric and piezoelectric properties were investigated. All specimens could be well sintered at a low-temperature of 1080 °C. The bulk density of the specimens doped with a small amount of Li₂CO₃ was enhanced. The dielectric and piezoelectric properties of ceramics were investigated with different amounts of Li₂CO₃ substitutions. High electrical properties of d₃₃ = 167 pC/N, k_p = 0.34, P_r = 40 μC/cm² and E_c = 38 kV/cm were obtained from the specimen containing 0.1 mol% of Li₂CO₃ sintered at 1080 °C.     

立方(Ba0.5Sr0.5)TiO3高压诱导带隙变化的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理计算研究了 (Ba_0.5Sr_0.5)TiO₃ (BST) 晶体在高压下的电子结构及能带变化行为. 研究结果发现,随着压强的增加,BST能带间隙先增加,在压强为55 GPa时达到最大值,然后减小,这些有趣的结果将有助于开发与设计新的BST铁电器件. 进一步地,通过电子态密度和密度分布图的研究分析可知:在低压区域(055 GPa),则是出现的离域现象占主导(电子的离域作用超过键态的作用),从而使带隙减小. 关键词： 钛酸锶钡 第一性原理 高压 能带间隙     

Self-assembled monolayers and chemical derivatization of Ba0.5Sr0.5TiO3 thin films: Applications in phase shifter devices

Thin films of barium strontium titanate (Ba_1−xSr_x TiO₃ (BSTO)) have been used in coupled microstrip phase shifters (CMPS) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability, and good structural stability. In an attempt to improve the figure of merit K (phase shift °/dB of loss) of phase shifters, modification of the metal/BSTO interface of these devices has been done through surface modification of the BSTO layer using a self-assembled monolayer approach. The impact of this nanotechnology promises to reduce RF losses by improving the quality of the metal/BSTO interface. In this study, compounds such as 3-mercaptopropyltrimethoxysilane (MPS), 16-mercaptohexadecanois acid (MHDA) and 3-mercaptopropionic acid (MPA) were used to form the self-assembled monolayers on the BSTO surface. As a result of the previous modification, chemical derivatization of the self-assembled monolayers was done in order to increase the chain length. Chemical derivatization was done using 3-aminopropyltrimethoxysilane (APS) and 16-mercaptohexadecanoic acid. Surface chemical analysis was done to reveal the composition of the derivatization via X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR). Low and high frequencies measurements of phase shifters were done in order measure the performance of these devices for insertion in antennas. X-ray photoelectron spectroscopy characterization of modified BSTO thin films with MPS showed a binding energy peak at 162.9 eV, indicative of a possible SO interaction: sulfur of the mercapto compound, MPS, used to modify the surface with the oxygen site of the BSTO thin film. This interaction is at higher binding energies compared with the thiolate interaction. This behavior is observed with the other mercapto compounds such as: MHDA and MPA. An FT-IR analysis present a band at 780 cm⁻¹, which is characteristic of an OSC stretching and reveals the modification of the BSTO thin film by the coupling of the O of the BSTO with the S of the mercapto compound. All the modification using mercapto compounds is through sulfur to the BSTO thin film. MHDA SAM on BSTO thin film was chemically derivatized using APS shown by XPS and FT-IR. The SAMs modified phase shifters showed an improvement in performance with respect to those phase shifters fabricated with standard methods.     

Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K0.5Na0.5NbO3- 0.04LiSbO3 lead-free piezoelectric ceramics

Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K0.5+xNa0.5+xNbO3- 0.04LiSbO3 lead-free piezoelectric ceramics were examined for 0 ≤ x ≤ 0.02. The piezoelectric coefficients exhibited a maximum, d33 = 187 pC/N at x = 0.0075, coinciding with the maximum of the grain size and the apparent density at x = 0.0075. The apparent density and the piezoelectric coefficients decreased with increasing x at higher x which was likely due to the crystal geometrical distortion of 0.96K0.5+xNa0.5+xNbO3-0.04LiSbO3. In addition, super-large grains were found and this may be due to liquid phase sintering. Excess (K++Na+) attracted a sum of space charges to keep the charge neutral, resulting in charge leakage during the course of ceramic polarization, influencing the piezoelectric and ferroelectric properties. These findings are of importance for guiding the design of K0.5Na0.5NbO3-based lead-free ceramics with enhanced electrical properties.     

Structural, electrical and optical properties of TiO2 doped WO3 thin films

TiO₂ doped WO₃ thin films were deposited onto glass substrates and fluorine doped tin oxide (FTO) coated conducting glass substrates, maintained at 500 °C by pyrolytic decomposition of adequate precursor solution. Equimolar ammonium tungstate ((NH₄)₂WO₄) and titanyl acetyl acetonate (TiAcAc) solutions were mixed together at pH 9 in volume proportions and used as a precursor solution for the deposition of TiO₂ doped WO₃ thin films. Doping concentrations were varied between 4 and 38%. The effect of TiO₂ doping concentration on structural, electrical and optical properties of TiO₂ doped WO₃ thin films were studied. Values of room temperature electrical resistivity, thermoelectric power and band gap energy (E_g) were estimated. The films with 38% TiO₂ doping in WO₃ exhibited lowest resistivity, n-type electrical conductivity and improved electrochromic performance among all the samples. The values of thermoelectric power (TEP) were in the range of 23-56 μV/K and the direct band gap energy varied between 2.72 and 2.86 eV.     

A位等价与非等价取代对(K0.5Na0.5)NbO3陶瓷极化的影响

研究了在铌酸钾钠基陶瓷中,A位等价与非等价取代对陶瓷极化温度和极化电场的影响,结果表明:A位等价取代的陶瓷对极化温度和极化电场没有强烈依赖性,可以使极化足够充分,能有效提高铌酸钾钠基陶瓷的压电性能;相反,A位非等价取代的陶瓷对极化温度和极化电场敏感,容易击穿,极化不充分,限制了铌酸钾钠基陶瓷的压电性能. 关键词： 铌酸钾钠 极化 压电     

Improving microwave dielectric properties of La2.98/3Sr0.01(Mg0.5Sn0.5)O3 ceramics with CuO additive

The microwave dielectric properties of CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were investigated with a view to their application in microwave devices. CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics exhibited no significant variation of phase with sintering temperature. By adding 0.75 wt.% CuO, a dielectric constant of 20.07, a quality factor (Q × f) of 63,000 GHz, and a temperature coefficient of resonant frequency τ_f (−77.0 ppm/°C) were obtained when La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were sintered at 1500 °C for 4 h.     

Microstructures and microwave dielectric properties of La1-xBx(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A maximum apparent density of 6.58 g/cm³, a dielectric constant (ε_r) of 19.8, a quality factor (Q × f) of 41,800 GHz, and a temperature coefficient of resonant frequency (τ_f) of −86 ppm/°C were obtained for La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1500 °C for 4 h.     

Effect of annealing temperature on microstructure, optical and electrical properties of sputtered Ba0.9Sr0.1TiO3 thin films

Ba_0.9Sr_0.1TiO₃ (BST) thin films were deposited on fused quartz and Pt/TiN/Si₃N₄/Si substrates by radio frequency magnetron sputtering technique. Microstructure and chemical bonding states of the BST films annealed at 700 °C were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and Raman spectrum. Optical constants including refractive indices, extinction coefficients and bandgap energies of the as-deposited BST film and the BST films annealed at 650, 700 and 750 °C, respectively, were determined from transmittance spectra by envelope method and Tauc relation. Dielectric constant and remnant polarization for the BST films increase with increasing annealing temperature. Leakage current density-applied voltage (J–V) data indicate that the dominant conduction mechanism for all the BST capacitors is the interface-controlled Schottky emission under the conditions of 14 V < V < 30 V and −30 V < V < −14 V. Furthermore, the inequipotential J–V characteristics for the BST films annealed at various temperatures are mainly attributed to the combined effects of the different thermal histories, relaxed stresses and strains, and varied Schottky barrier heights in the BST/Pt and Pt/BST interfaces.     

纳米Cu3N薄膜的制备与性能

采用柱状靶多弧直流磁控溅射法，100℃基底温度下在玻璃衬底上制备了纳米氮化铜(Cu3₃N)薄膜.用x射线衍射研究了不同氮气分压对Cu3₃N薄膜晶体结构 及晶粒尺寸的影响.结果显 示薄膜由Cu3₃N和Cu的纳米微晶复合而成，其中Cu3₃N纳米微晶具有 立方反ReO3₃结构.通 过原子力显微镜对薄膜表征显示，膜表面比较光滑，具有较低的粗糙度.x射线光电子能谱对 薄膜表面的成分分析表明，Cu3 _{关键词： 氮化铜薄膜 多弧直流磁控溅射 3}结构')" href="#">立方反ReO3₃结构     

Transverse laser induced thermoelectric voltage effect in tilted La0.5Sr0.5CoO3 thin films

The transverse laser induced thermoelectric voltage effect has been investigated in tilted La_0.5Sr_0.5CoO₃ thin films grown on vicinal cut LaAlO₃ (1 0 0) substrates when films are irradiated by pulse laser at room temperature. The detected voltage signals are demonstrated to originate from the transverse Seebeck effect as the linear dependence of voltage on tilted angle in the range of small tilted angle. The Seebeck coefficient anisotropy ΔS of 0.03 μV/K at room temperature is calculated and its distorted cubic structure is thought to be responsible for this. Films grown on a series of substrates with different tilted angles show the optimum angle of 19.8° for the maximum voltage. Film thickness dependence of voltage has also been studied.