Pyroelectric properties of sol-gel derived PZT thin films with various Zr/Ti ratios

Abstract

Integrated pyroelectric arrays are receiving serious attention for the next generation of room temperature uncooled IR cameras. Such pyroelectric arrays are based on monolithic ferroelectric(FE) thin films. FE films with large values of reported pyroelectric coefficients include PbTiO₃, Ca-doped PbTiO₃, La-doped PbTiO₃, PZT 53/47 and Pb(Sc_0.5Ta_0.5)O₃. The present paper reports a systematic study of the compositional dependence of PZT thin films on their pyroelectric properties. A series of sol-gel derived PZT (lead zirconate titanate) thin films with various Zr/Ti ratios, namely, PbTiO₃, PZT 20/80, PZT 35/65, PZT 53/47, PZT 65/35, PZT 92/8 and PbZrO₃, were prepared on platinized Si substrates. The films were fired to 650 – 700°C to crystallize them into single-phase perovskite. The degree of preferred orientation, grain size and firing temperature affect the pyroelectric responses. Pyroelectric coefficients as large as 2.5 × 10^?8 C/cm²-K were obtained, making such PZT thin films attractive in pyroelectric arrays.     

Electrical properties of PLZT thin films formed by photochemical metal-organic deposition with various Zr/Ti ratios

Lanthanum-doped lead zirconate titanate (PLZT) films formed by photochemical metal-organic deposition using photosensitive starting precursors were characterized. The substitution of La for Pb was found to induce the improved ferroelectric properties, especially fatigue property through the reduction of oxygen vacancies with excess electrons. But remnant polarization was reduced, because the doping of La gives the same effect as shift of composition of Zr/Ti ratio in PLZT film from morphotropic phase boundary composition of PZT(Zr/Ti ratio of 56/44). The measurement results of polarization-electric field and capacitance-voltage indicate that the composition of maximum ferroelectric properties of PLZT film shifts toward Ti-rich side between 52/48 and 48/52 of Zr/Ti ratio. A decrease in Zr/Ti ratio induced an improvement in I-V and fatigue properties due to the low defect concentration such as Pb or O vacancies and the inter-grain depletion of grain boundary limited conduction.     

Characterization of Ba(Zr0.05 Ti0.95)O3 thin film prepared by sol-gel process

Ba(Zr_0.05Ti_0.95)O₃ (BZT) thin film (∼330 nm) was grown on Pt/Ti/SiO₂/Si(100) substrate by a simple sol-gel process. The microstructure and the surface morphology of BZT thin film were studied by X-ray diffraction and atomic force microscopy. The optical properties of BZT thin film were obtained by spectroscopic ellipsometry. The optical bandgap was found to be 3.74 eV of direct-transition type. Ferroelectric and dielectric properties of BZT thin film were also discussed. The electrical measurements were conducted on BZT films in metal-ferroelectric-metal (MFM) capacitor configuration. The results showed the film exhibited good ferroelectrity with remanent polarization and coercive electric field of 3.54 μC/cm² and 95.5 kV/cm, respectively. At 10 kHz, the dielectric constant and dielectric loss of the film are 201 and 0.029, respectively.     

High-deposition-rate growth of PZT thin films by reactive electron beam coevaporation using Ti/Zr alloy

Abstract

Lead zirconate titanate (PZT) thin films were prepared by coevaporation of titanium/zirconium alloy and lead metal with an electron beam gun. Each of evaporation rates was independently controlled by each quartz crystal thickness monitor. Titanium/zirconium alloy was used because of simplicity of chemical composition control. To promote oxidation of the films, a mixed gas of oxygen and ozone (5%) was used. When evaporation rates of titanium/zirconium alloy and lead metal were controlled moderately, perovskite phase PZT film was obtained on 50 nm-thick-PbTiO₃-film at substrate temperature of 550°C. When atomic ratio of titanium/zirconium alloy was 50:50, chemical composition of the films was Ti:Zr = 9:1. Deposition rate was greater than 50 nm/min, which was much larger than that by the sputtering method.     

Photosensors based on Ni-doped ZnO/p-Si junction prepared by sol-gel method

A high quality and adherent transparent layer of ZnO thin films were grown on p-type Si substrates to fabricate undoped and Ni-doped ZnO/p-Si heterojunction. The C _Adj ?V and G _Adj ?V plots of the diodes are significantly affected with the frequency and Ni-dopant contents. The interface state density (D _it ) is changed with the frequency and Ni contents. The high value of ideality factor (n) is due to the interface states at the interface of the diode and the effect of barrier inhomogeneities or to the high value of R _s . The transient photocurrent measurements were used to analyze the photoresponse of the diodes. The obtained results indicate that the diodes could be used as an optical sensor especially for the Ni-doped at 0.5 % ZnO/p-Si diode.     

Electrical and optical properties of PZT ferroelectric films fabricated by the PVP-assisted sol-gel method

Lead zirconate titanate (PZT) films were deposited on platinized silicon substrates by spin coating using organic macromolecule polyvinylpyrrolidone (PVP) as an additive, which has the hybrid effects, was dispersed uniformly into the sol-gel precursor solution of PZT. The films were coated by spin-coating and then annealed at a proper temperature by repaid thermal processing. PZT ferroelectric films were polycrystalline and perovskite phase structure. The Coercive Field and remnant polarization of the PZT films annealed at 600 °C were 91 kV/cm and 19 μC/cm² respectively. The fatigue resistance properties were improved and the polarization value decreased only 8% of the initial polarization at 10⁸ cycles. The optical properties were measured by spectrophotometer and the band energy was calculated about 3.59eV.     

尖晶石型LiMn2O4的电化学性质

利用循环伏安法(CV)、恒流充放电、电化学阻抗谱(EIS)等电化学手段研究了溶胶凝胶法制备的尖晶石型LiMn2O4的电化学性质.结果表明用溶胶凝胶法制备的样品放电容量大,可逆性好,其中550℃煅烧的样品电化学性能最好;XRD结果表明,样品经过充放电,尖晶石结构仍保留,但出现深度放电产物Li2Mn2O4.     

Electrical properties of TiO2 thin films prepared by the sol-gel method

A TiO₂ thin film was prepared by the sol-gel method using a metal alkoxide [Ti(O-i-Pr)₄ tetrasopropoxy titanium: TIPT]. The crystalline form of the film depends on the preparation conditions and the heat treatment temperature. When the ratio (γ) of H₂O to TIPT is 7, the crystalline phase is formed at 400°C; when γ = 2 it is formed at 500°C. The anatase crystal structure was obtained for both γ = 2 and γ = 7. The electrical conductivity of the TiO₂ film increased with the heat treatment temperature.     

溶胶-凝胶法制备纳米LaMnO_3的电催化活性

采用表面活性剂聚乙二醇-2000辅助溶胶-凝胶法,制备锌-空气电池催化剂锰酸镧(LaMnO_3)。通过热重-差示扫描量热(TG-DSC)法、XRD、傅里叶变换红外光谱(FTIR)、透射电子显微镜(TEM)和极化曲线,研究催化剂LaMnO_3的结构和电催化活性。较优的制备工艺为:初始pH值为6.5,表面活性剂与金属离子物质的量比为0.018∶1.000,在700℃下煅烧3 h。制备的LaMnO_3为钙钛矿结构,晶体成型温度在450℃左右、晶粒尺寸处于纳米级别,具有良好的氧还原电催化活性。以LaMnO_3为催化剂的电极在电位为-600 mV(vs.Hg/HgO)时的输出电流密度为0.165 A/cm~2。     

Structure of sol-gel prepared ferroelectric Bi3.4La0.6Ti3O12

The Bi_3.4La_0.6Ti₃O₁₂ (BLT) thin film and powder have been prepared by a sol-gel method with annealing at 700^°C. Randomly oriented BLT thin film exhibits a large remanent polarization, 2P _r = 72 μC/cm², with a dc applied field strength of 320 kV/cm. Structure of sol-gel derived BLT powder has been investigated by neutron scatterings, and refined by a Rietveld method resulting a reasonable goodness of fit (wR _p = 6.7%, and R _p = 5.7%) using an orthorhombic (B2cb, a = 5.4221 Å, b = 5.4032 Å, and c = 32.8361 Å). Two different TiO₆ octahedra exhibit different polarization directions; (100) from Ti(1)O₆, and (011) from Ti(2)O₆, which explains the observed large 2P _r of the randomly oriented BLT thin film.     

Dielectric behavior of hexagonal and orthorhombic YFeO3 prepared by modified sol-gel method

Polycrystalline YFeO₃ ceramic powders were synthesized by modified polyacrylamide sol-gel method. X-ray diffraction analysis demonstrated that the crystal structures of YFeO₃ could be controlled from hexagonal phase (h-YFeO₃) to orthorhombic phase (o-YFeO₃) through the calcined temperature. Temperature-dependent dielectric constants (ε _r) and losses (tanδ) show that strong frequency dispersion phenomena occur in whole measuring temperature. Both the h-YFeO₃ and o-YFeO₃ exhibit dielectric relaxation behavior at T?<?250 K and at T?>?340 K, which could be attributed to thermal activation. Whereas, only h-YFeO₃ shows an anomaly dielectric peak at T _m ?=?297 K fitted with Curie-Weiss law and modified Curie-Weiss law, indicating a possible P6 ₃ mc-P6 ₃ cm transition with slightly diffuse characteristics.     

溶胶-凝胶法制备的Li_(1.15)V_3O_8的电化学性能

以Li2CO3和NH4VO3为原料,分别采用柠檬酸和酒石酸为螯合剂,通过溶胶-凝胶法制备了正极材料Li1.15V3O8。用红外光谱、TG-DTG、XRD和SEM等方法对前驱体和产物进行分析,并进行了电化学性能测试。用酒石酸制备的Li1.15V3O8,首次放电比容量比用柠檬酸制备的高,且循环性能较好,以0.14 mA在1.8～3.9 V充放电的首次放电比容量为190.17 mAh/g,在第32次和第47次循环时达到210.99 mAh/g,循环过程中容量折线上升。     

酸催化溶胶凝胶法制备细菌纤维素/SiO_2复合隔膜

在细菌纤维素水凝胶中,用酸催化正硅酸乙酯水解,原位生成纳米级Si O2粒子,压缩干燥后,得到细菌纤维素(bacterial cellulose,BC)/Si O2复合隔膜,并对该复合膜的微观形貌、热稳定性以及电化学性能等进行了测试和分析。热重分析(TGA)及热收缩测试表明该BC/Si O2复合膜在200℃以下具有较好的热稳定性(零收缩);BC/Si O2复合膜的锂离子电导率在常温下(25℃)可以达到2.10×10-4 S/cm;此外,BC/Si O2复合膜在Li/Li Fe PO4半电池中表现出很好的化学和电化学稳定性。所制备的BC/Si O2复合膜有望在锂离子电池中得到应用。     

溶胶凝胶法制备高性能LiMn2O4薄膜

用溶胶凝胶法在Pt片上采用慢速旋转涂布工艺制备LiMn2O4薄膜.该膜表面呈非致密态,厚度在200 nm左右,晶体颗粒大小约为100nm.实验表明:该膜具有较大的放电容量,电流密度在0.01 mA/cm2时,容量可达到75μAh/cm2·μm;可承受1 mA/cm2的电流密度放电,容量仍有49μAh/cm2·μm.该膜循环性能良好,400次循环后容量没有衰减.     

溶胶-凝胶法制备Li_4Ti_5O_(12)/C复合负极材料及性能研究

以醋酸锂、钛酸丁酯为原料,草酸为络合剂和碳源,采用溶胶-凝胶法氮气气氛中合成锂离子电池负极材料Li4Ti5O12/C,研究了锂源过量与否对材料结构和电化学性能的影响。采用XRD、SEM对材料的晶体结构和微观形貌进行表征,采用恒流充放电循环测试对材料的电化学性能进行表征。结果表明:当锂源过量5%时,合成的Li4Ti5O12/C材料为单一的尖晶石结构,且样品粒径较小(约100~150 nm),有利于锂离子的嵌入与脱出。其在0.2、1.0、2.0 C和5.0 C时的首次放电比容量分别为182.5、162.7、155.7 mAh/g和155.3 mAh/g,且5.0 C倍率下循环50次后仍达153.9mAh/g,表现出较好的高倍率放电性能和循环稳定性。     

Dielectric properties for Tantalum-doped strontium barium titanate thin films prepared by sol-gel method

In this work, Sr_0.5Ba_0.5Ti_1-zTa_zO₃ (SBT) thin films were prepared on a Pt/SiO₂/Si substrate by sol-gel process. The microstructures of SBT thin films were examined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The influences of Ta on the microstructure and dielectric properties of SBT thin films were studied. It is found that tetragonal perovskite crystal grains existed in SBT thin films. Ta⁵⁺ doping fines the grain of SBT thin films. It is found that Ta⁵⁺ doping decreases dielectric loss for SBT thin films.     

溶胶-凝胶法制备球形负极材料Li4Ti5O12

以二乙醇胺为抑制剂、Ti(OC4H9)4和CH3COOLi为原料,用溶胶-凝胶法制备球形负极材料钛酸锂(Li4Ti5O12)。用TG、XRD、SEM和电化学性能测试,研究了煅烧温度和时间的影响。最佳条件为:在750℃下煅烧12 h。在此条件下合成的样品具有典型的尖晶石结构和球形形貌,在0.5～3.0 V以0.1C循环,首次放电比容量为167.1 mAh/g,循环性能良好。     

溶胶凝胶法制备Li_4Ti_5O_(12)/C负极材料及电化学性能

采用溶胶凝胶法,以有机物钛酸四丁酯和醋酸锂为原料,草酸为螯合剂,PEG为碳源制备出Li_4Ti_5O_(12)/C复合材料前驱体,在N_2气氛中850℃高温煅烧制备出Li_4Ti_5O_(12)/C复合材料。通过XRD、SEM分析表明,850℃下煅烧10 h合成结晶性良好的亚微米级纯相尖晶石钛酸锂。电化学性能测试结果表明,Li_4Ti_5O_(12)/C在0.2C,1C,2C倍率下的首次放电比容量分别为173.3、168.7、166.3 mAh/g。与Li_4Ti_5O_(12)相比,显示出良好的倍率性。     

溶胶-凝胶法合成钛酸锂及石墨烯的掺杂改性

采用溶胶-凝胶法合成了纯相、结晶度高、粒径为40~100 nm的钛酸锂粉体,使用X射线衍射(XRD)、扫描电镜(SEM)和投射电子显微镜(TEM)技术对样品进行了物相分析和形貌表征。优化条件为:反应物摩尔比Li/Ti=4.2/5~4.4/5、煅烧温度700~750℃、煅烧时间9~12 h。对钛酸锂进行石墨烯掺杂改性的方法是,将自制的钛酸锂粉体、氧化石墨粉体和水合肼按比例混合在一起,经100℃油浴加热24 h即可得到的石墨烯掺杂改性钛酸锂的复合材料,此材料仍为尖晶石型结构,结晶度高、分散性好且无杂质生成。经测试,Li4Ti5O12样品首次放电比容量达到163 mAh/g,改性后Li4Ti5O12复合材料首次放电比容量提高,达到175 mAg/h。     

Characteristics of barium hexaferrite nanocrystalline powders prepared by a sol-gel combustion method using inorganic agent

Nanocrystalline particles of barium hexaferrite were synthesized by a sol-gel combustion route using nitrate-citrate gels prepared from metal nitrates and citric acid solutions under various Fe/Ba molar ratios of 10, 11 and 12. Sodium hydroxide was used as a pH-adjusting agent. The results revealed that the formation temperature of barium hexaferrite is influenced by Fe/Ba molar ratio; the Fe/Ba molar ratio of 12 is more favorable. For sample synthesized with a Fe/Ba molar ratio of 12, barium hexaferrite started to form at 800 °C and fully formed at 1000 °C. The results also showed that the coercivity of the samples decreases as the Fe/Ba molar ratio increases from 10 to 12, whilst the saturation magnetization increases.