ZnAl_2O_4和La_2O_3对Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷介电性能的影响

通过传统的固相反应合成掺杂ZnAl_2O_4和La~(3+)(来自La_2O_3)的Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷粉体,干压成型后在空气气氛下常压烧结制备ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品。分别研究了La~(3+)和ZnAl_2O_4的掺杂量对复合陶瓷样品的微观形貌、相组成和介电性能的影响。结果表明:ZnAl_2O_4具有细化晶粒的作用;Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品的致密度随La~(3+)和ZnAl_2O_4含量的增加而增加;介电常数和谐振频率温度系数随ZnAl_2O_4含量的增加而减小,随La_2O_3添加量变化不大;品质因数值随ZnAl_2O_4含量的增加先增加后减小。制备出的ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷致密度达到94%以上,介电常数在40~50之间,谐振频率温度系数小于40×10~(-6)℃~(-1),品质因数大于38 000GHz,可以用于通信技术领域。     

Effects of Pb2+ doping on La4Ti9O24 ceramics

The kinetic structural evolution of the Pb²⁺-doped La₄Ti₉O₂₄ ceramics was investigated. Using electron diffraction and Rietveld analysis of the X-ray powder diffraction patterns, we show that the increase in Pb²⁺ doping results in the structural transition from La₄Ti₉O₂₄ to a La_2/3TiO₃-type phase (Ibmm, No. 74). Further kinetic studies of Pb²⁺ diffusion into La₄Ti₉O₂₄ ceramics suggest that the La₄Ti₉O₂₄–La_2/3TiO₃ phase transition requires an activation energy of 607 ± 60 kJ/mol.     

Phase formation and microwave dielectric properties of Pb2+ and Sr2+ doped La4Ti9O24 ceramics

Phase formation and microwave dielectric properties of the Pb²⁺ and Sr²⁺ doped La₄Ti₉O₂₄ ceramics were investigated. Using electron diffraction and Rietveld analysis of the X-ray powder diffraction patterns, we show that the increase in the concentration of Pb²⁺ and Sr²⁺ doping results in the structural transition from La₄Ti₉O₂₄ to a La_2/3TiO₃-type phase (Ibmm, No. 74). A change in the crystalline phase considerably affects the microwave dielectric properties, increasing the ɛ_r from 37 to 130, reducing Q × f from 25,000 to 5500, and increasing temperature coefficient of the resonant frequency (TCF) from 15 to 300 ppm/°C.     

Microstructural and dielectric properties of donor doped (La3+) CaCu3Ti4O12 ceramics

The effect of La³⁺ doping on Ca²⁺ sites in CaCu₃Ti₄O₁₂ (CCTO) was examined. Polycrystalline samples in the chemical formula Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ with x = 0, 0.5, 1 were synthesized via the conventional solid state reaction route. X-ray powder diffraction analysis confirmed the formation of the monophasic compounds and indicated the structure to be remaining cubic with a small increase in lattice parameter with increase in La³⁺ doping. The dielectric and impedance characteristics of Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ were studied in the 100 Hz–10 MHz frequency range at various temperatures (100–475 K). A remarkable decrease in grain size from 50 μm to 3–5 μm was observed on La³⁺ substitution. The dielectric constant of CaCu₃Ti₄O₁₂ decreased drastically on La³⁺ doping. The frequency and temperature responses of dielectric constant of La³⁺ doped samples were found to be similar to that of CaCu₃Ti₄O₁₂. The effects of La³⁺ doping on the electrical properties of CaCu₃Ti₄O₁₂ were probed using impedance spectroscopy. The conducting properties of grain decreased while that of the grain boundary increased on La³⁺ doping, resulting in a decrease of the internal barrier layer effect. A decrease in grain boundary capacitance and stable grain response in La³⁺ doped CCTO ceramics were unambiguously established by modulus spectra studies.     

Microstructure and dielectric properties of CaCu3Ti4O12 ceramic

CaCu₃Ti₄O₁₂ (CCTO) was prepared by the solid state technique. The sample was calcined at 900 °C/12 h and sintered at 1050 °C/24 h, then subjected to XRD to ensure CCTO formation. The microstructure was observed by SEM. XRD results identified both samples as single phase CCTO, whereas the microstructure shows abnormal grain growth and large pores. Sintering was studied in the temperature range of 950–1050 °C for 3–12 h. Increasing sintering temperature enhances the density and secondary formation of Cu₂O. A clear grain boundary and dense microstructure were observed. The results show that the sample sintered at 1040 °C/10 h yields a clearly uniform grain size with the highest ε_r (33,210).     

La2O3掺杂对BST/MgO复合陶瓷显微结构和性能的影响

采用固相反应法制备了未掺杂和La2O3掺杂(0.5%、1%、2%(摩尔分数))的Ba0.55Sr0.45TiO3/MgO复合陶瓷材料,并研究了它们的显微结构和各种介电性能.研究结果表明,La2O3除一部分会进入BST晶格獭代Ba或Sr的位置外,还会有一部分与MgO等形成无定形态物质滞留在晶界,起到抑制BST晶粒生长的作用.BST/MgO复合陶瓷的居里温度随La2O3掺杂量的增大而降低,居里温度的降低导致了介电常数的减小.适量的La2O3掺杂提高了复合陶瓷的调谐性,而且La2O3掺杂明显降低了复合陶瓷的微波介电损耗.0.5%(摩尔分数)La2O3掺杂的BST/MgO复合陶瓷具有最佳的综合介电性能,其在10kHz下的调谐性为6.9%(2kV/mm),3.99GHz时的介电常数和介电损耗分别为87.5和3.35×10-3,基本可以满足铁电移相器的使用要求.     

Influence of Zn doping on microstructure,dielectric, and electric properties in Bi2/3Cu3Ti4O12 ceramic synthesized by the semi-wet method

Journal of Materials Science: Materials in Electronics - Zn-doped and undoped BCTO ceramics (Bi2/3Cu3?xZnxTi4O12, where x?=?0, 0.05, 0.1, and 0.2) were prepared by semi-wet...     

Sintering behavior and dielectric properties of polycrystalline CaCu3Ti4O12

Sintering behavior and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) have been studied. CCTO phase was formed at 950 °C. A two-step sintering method was employed. The pressed green body of CaCu₃Ti₄O₁₂ was first heated to 1,080 °C to achieve an intermediate density (>75% of theoretical density), then cooled down and held at 950 °C for 0–20 h until it was fairly dense. A slight grain growth was observed for 20 h holding time with a significant increase in density from 81% to 92% of theoretical density. The average grain size of dense ceramics was ~6 μm and the bulk density was 4.7 g/cm³. The normally sintered specimen at 1,070 °C exhibited slightly higher density (4.8 g/cm³, 95%) with bimodal grain size. Normal sintering also yielded higher dielectric constants than the specimens processed by the two-step sintering.     

Non-Ohmic and dielectric properties of Ba-doped CaCu3Ti4O12 ceramics

The microstructure, dielectric and electrical properties of Ca_1?x Ba _x Cu₃Ti₄O₁₂ (where x = 0, 0.025, and 0.05) ceramics were investigated. Our microstructural analyses revealed that Ba²⁺ doping ions preferentially form in a secondary phase, and are not introduced into the CaCu₃Ti₄O₁₂ lattice. Grain growth rate of CaCu₃Ti₄O₁₂ ceramics was significantly inhibited by the Ba-related secondary phase particles, resulting in a large decrease in their mean grain size. The dielectric permittivity of CaCu₃Ti₄O₁₂ ceramics decreased with increasing Ba content. Their loss tangent decreased after addition of CaCu₃Ti₄O₁₂ with 2.5 mol% of Ba²⁺, and increased with increasing Ba contents to 5.0 mol%. The nonlinear coefficient and breakdown field of the Ca_1?x Ba _x Cu₃Ti₄O₁₂ ceramics were significantly enhanced by adding 2.5 mol% of Ba²⁺, followed by a slight decrease as Ba²⁺ concentration was increased to 5.0 mol%. Using impedance spectroscopy analysis, it was revealed that variations in dielectric and non-Ohmic properties are associated with electrical response of grain boundaries. This supports the internal barrier layer capacitor model.     

A位掺杂Bi4Ti3O12陶瓷的铁电性能研究

用传统固相烧结工艺,制备了纯相的Bi4Ti3O12 (BTO)陶瓷,A位掺杂的Bi3.25La0.75Ti3O12(BLT),Bi3.15Nd0.85Ti3O12(BNdT)铁电陶瓷.X射线衍射结果表明,所有样品均为单一的层状钙钛矿结构,La、Nd掺杂未改变BTO的晶体结构.铁电测试结果表明,BTO、BLT和BNdT陶瓷的剩余极化2Pr值分别为12.4、23.8和39.4μC/cm2.A位掺杂后,BLT、BNdT的2Pr值比未掺杂的BTO分别提高了1.92和3.18倍.漏电流测试表明,BLT、BNdT陶瓷的漏电流密度比BTO明显降低.A位掺杂显著提高了BTO陶瓷的铁电性能.     

Schottky barrier versus surface ferroelectric depolarization at Cu/Pb(Zr,Ti)O3 interfaces

The band bending at Cu/PZT(001) interfaces is investigated by X-ray photoelectron spectroscopy (XPS) for a PZT(001) layer which exhibits initial outwards ferroelectric polarization. Two competitive processes are identified: (a) formation of the Schottky barrier between the ferroelectric and unconnected Cu islands, and (b) coalescence of the Cu islands, realisation of an electrical contact to the ground of the system, inducing the apparent loss of the component of the ferroelectric polarization perpendicular to the sample surface, at least as it manifests in band bending. Three mechanisms are proposed to explain this loss of band bending when a full metal layer connected to ground is formed on the surface: (i) over-compensation of depolarization field in the sub-surface region, (ii) formation of domains with in-plane orientation of the polarization vector and (iii) loss of polarization in the near-surface layers of the ferroelectric due to electrons provided by the metal. These result in a non-monotonous variation of binding energies with the amount of Cu deposited. High resolution transmission electron microscopy and piezoresponse force microscopy confirmed these hypotheses. The XPS data allowed also to derive the surface PZT composition, its evolution with the deposition of copper and the formation of surface compounds.     

Structural and dielectric properties of La substituted polycrystalline Ca(Ti0.5Fe0.5)O3

Polycrystalline Ca_1?x La _x (Ti_0.5Fe_0.5)O₃ were prepared by the standard solid state reaction technique. Pellet shaped samples prepared from each composition were sintered at 1573 K for 5 h. The X-ray diffraction analysis indicated the formation of a single-phase orthorhombic structure. The lattice parameters as well as densities increased but the average grain sizes decreased with the increase of La content. The dielectric measurements were carried out at room temperature as a function of frequency and composition. The experimental results revealed that dielectric constant (?′) decreased but dielectric loss (tan δ) and ac electrical conductivity (σ _ac ) increased as frequency increased. The composition dependence of ?′ and tan δ indicated that they decreased with the increase of La content. The σ _ac was derived from the dielectric measurements and it is concluded that the conduction in the present samples is due to mixed polarons hopping.     

Modified giant dielectric properties of samarium doped CaCu3Ti4O12 ceramics

Effects of Sm³⁺ substitution on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ ceramics were investigated. The grain size of CaCu₃Ti₄O₁₂ ceramics was greatly decreased by doping with Sm³⁺, resulting from the ability of Sm³⁺ to inhibit the grain growth rate. This result can cause a decrease in the dielectric constant (?′) and loss tangent (tan δ) of CaCu₃Ti₄O₁₂ ceramics. Interestingly, high dielectric permittivity (?′ ～ 10,863) and low loss tangent (tan δ ～ 0.043 at 20 °C and 1 kHz) were observed in the Ca_0.925Sm_0.05Cu₃Ti₄O₁₂ ceramic. Nonlinear electrical properties of CaCu₃Ti₄O₁₂ ceramics were modified by doping with Sm³⁺. The dielectric relaxation behavior of Sm-doped CaCu₃Ti₄O₁₂ ceramics can be well ascribed based on the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.     

Dielectric properties and electrical response of grain boundary of Na1/2La1/2Cu3Ti4O12 ceramics

The dielectric properties and electrical response of grain boundaries of Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics were investigated as a function of temperature. High dielectric permittivity (6.1–8.7 × 10³) and low loss tangent (0.032–0.038 at 10 kHz) were observed in Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics. Through analyses using complex impedance and electric modulus, it was found that the dielectric properties of Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics are closely related to the electrical response of grain boundaries. The investigation of non-Ohmic characteristics at various temperatures suggests that the potential barrier at the grain boundaries of Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics is due to the Schottky effect. The giant low frequency dielectric response in Na_1/2La_1/2Cu₃Ti₄O₁₂ ceramics is attributed to Maxwell–Wagner polarization at the grain boundaries.